Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories | Lex Fridman Podcast #430
- The act of remembering
can change the memory. If you remember some event, and then I tell you
something about the event, later on when you remember
the event you might remember some original information from the event, as well as some information
about what I told you. And sometimes if you're not
able to tell the difference, that information that
I told you gets mixed into the story that you had originally. So now I give you some
more misinformation, or you're exposed to some more information somewhere else, and eventually your memory becomes totally detached
from what happened. - The following is a conversation
with Charan Ranganath, a psychologist and
neuroscientist at UC Davis specializing in human memory. He's the author of "Why We Remember: Unlocking Memory's Power to
Hold on to What Matters." This is the "Lex Fridman Podcast." To support it, please
check out our sponsors in the description. And now, dear friends,
here's Charan Ranganath. Danny Kahneman describes
the experiencing self and the remembering self and that happiness and
satisfaction you gain from the outcomes of your
decisions do not come from what you've experienced, but rather from what you
remember of the experience. So can you speak to this
interesting difference that you write about in your book, of the experiencing self
and the remembering self? - Danny really impacted me,
'cause I was an undergrad at Berkeley and I got to
take a class from him, long before he won the
Nobel Prize or anything. And it was just a mind blowing class. But this idea of the remembering self and the experiencing self, I got into it because
it's so much about memory, even though he doesn't study memory. So we're right now having
this experience, right? And people can watch it
presumably on YouTube, or listen to it on audio, but if you're talking to somebody else, you could probably describe
this whole thing in 10 minutes. But that's going to miss a
lot of what actually happened. And so the idea there is
is that the way we remember things is not the replay
of the experience, it's something totally different, and it tends to be biased by
the beginning and the end, and he talks about the peaks, but there's also the, you
know, the the best parts, the worst parts, et cetera. And those are the things that we remember. And so when we make decisions,
we usually consult memory and we feel like our memory is a record of what we've experienced, but it's not, it's this
kind of very biased sample, but it's biased in an interesting and, I think, biologically relevant way. - So in the way we construct
a narrative about our past, you say that it gives us
an illusion of stability. Can you explain that? - Basically I think that a
lot of learning in the brain is driven towards being
able to make sense. I mean really memory is
all about the present and the future. The past is done, so,
biologically speaking, it's not important, unless there's something
from the past that's useful. And so what our brains
are really optimized for is to learn about
the stuff from the past that's going to be most useful
in understanding the present and predicting the future. Right? And so cause-effect
relationships for instance, that's a big one. Now my future is completely unpredictable in the sense that like
you could, you know, in the next 10 minutes pull a knife on me and slit my throat. Right? - I was planning on it. - Exactly. But having seen some of your work and just, you know, generally
my expectations about life, I'm not expecting that. I have a certainty that
everything's gonna be fine, we're gonna have a great
time talking today. Right? But we're often right. It's like, okay, so I go
to see a band on stage, you know, I know they're
gonna make me wait, the show's gonna start late and then, you know, they come on, there's a very good chance
there's gonna be an encore. I have a memory, so to
speak, for that event before I've even walked into the show. Right? There's gonna be people
holding up their camera phones to try to take videos of it now, 'cause this is kind of
the world we live in. So that's like everyday fortune telling that we do though. It's not real, it's imagined. And it's amazing that
we have this capability, and that's what memory is about. But it can also give us the
illusion that we know everything that's about to happen. And I think what's valuable
about that illusion is when it's broken it
gives us the information. Right? So I mean, you know, I'm
sure being in AI you know about information theory. And the idea is the information is what you didn't already have. And so those prediction errors
that we make based on... You know, we make a
prediction based on memory, and the errors are where the action is. - The error is where the learning happens? - Exactly. Exactly. - Well just to linger on Danny Kahneman, and just this whole idea
of experiencing self versus remembering self,
I was hoping you can give a simple answer of how we should live life based on the fact that our
memories could be a source of happiness, or could be the
primary source of happiness. That an event, when experienced,
bears its fruits the most when it's remembered over
and over and over and over. And maybe there is some wisdom in the fact that we can
control, to some degree, how we remember it, how
we evolve our memory of it such that it can maximize
the long-term happiness of that repeated experience. - Okay, well first I'll
say, I wish I could take you on the road with me, because that was such a great description. - Can I be your opening act, or... - Oh my god, no, I'm
gonna open for you, dude. Otherwise it's like, you
know, everybody leaves after you're done. (both laughing) Believe me, I did that
in Columbus, Ohio once. It wasn't fun. Like the opening acts
like drank our bar tab. We spent all this money
going all the way there, there was only the... Everybody left after the
opening acts were done and there was just that stoner dude with the dreadlocks hanging out. And then next thing you know
we blew like our savings on getting a hotel room. - So we should, as a small tangent, you are a legit touring act? - When I was in grad
school I played in a band and, yeah, we traveled,
we would play shows. It wasn't like... We weren't a hardcore touring band, but we did some touring
and had some fun times. And, yeah, we did a movie soundtrack. - Nice. - "Henry: Portrait of Serial Killer." So that's a good movie. We were on the soundtrack for the sequel, "Henry 2: Mask of Sanity,"
which is a terrible movie. - Yeah. How's the soundtrack? Is it pretty good?
- It's badass. - All right.
- At least that one part where the guy throws up the milkshake. - Okay, all right.
- Which is my song. - We're gonna have to see. We're gonna have to see it. - [Charan] All right, we'll
get you back to life advice- - And happiness, yeah. - One thing that I try to
live by, especially nowadays, and since I wrote the
book I've been thinking more and more about this, is how do I want to live a memorable life? You know, I think if we go back
to like the pandemic, right? How many people have
memories from that period? Aside from the trauma of
being, you know, locked up and seeing people die, and all this stuff. I think it's like one of these
things where we were stuck inside looking at screens all day, doing the same thing with the same people, and so I don't remember much from that in terms
of those good memories that you're talking about. Right? You know, when I was
growing up my parents worked really hard for us and, you
know, we went on some vacations, but not very often. And I really try to do now
vacations to interesting places as much as possible with my family because like those are the
things that you remember, right? So I really do think
about what's going to be like something that's memorable, and then just do it, even
if it's a pain in the ass, because the experiencing self will suffer for that, but the remembering
self will be like, "Yes, I'm so glad I did that." - Do things that are very
unpleasant in the moment, because those can be reframed and enjoyed for many years to come. That's probably... Good advice. Or at least when you're going
through shit it's a good way to see the silver lining of it. - Yeah, I mean I think
it's one of these things where if you have like people
who you've gone through. I mean, since you said it, I'll just... Since you've gone through
shit with someone. - [Lex] Yeah. - And it's like, that's a
bonding experience often. You know? I mean that can really bring you together. I like to say it's like
there's no point in suffering unless you get a story out of it. (Charan laughing) So in the book I talk about the power of the way we communicate with others and how that shapes our memories. And so I had this near death experience, at least that's how I remember it, on this paddle board where just everything that could have gone wrong
did go wrong, almost. So many mistakes were made and
ended up, like at some point, just like basically away from
my board pinned in a current, like in this corner, like
not a super good swimmer. And my friend who came with me, Randy, who's a computational neuroscientist, and he had just been pushed down past me and so he couldn't even see me. And I'm just like, "If I die
here, you know, I mean no one's around, it's like you just die alone." And so I just said, "Well,
failure's not an option." And eventually I got out of
it and froze, and got cut up. I mean the things that
we were going through were just insane. But short version of this
is, you know, my wife and my daughter, and
Randy's wife, they gave us all sorts of hell about this, 'cause they were just like, where are... They were ready to send
out a search party. So they were giving me hell
about it, and then I started to tell people in my lab
about this, and then friends, and it just became a better
and better story every time. And we actually had some photos of just the crazy things. Like this generator that
was hanging over the water and we're like ducking under the zig of these metal gratings,
and I'm like going flat. And it was just nuts, you know? But it became a great story. And it was definitely... I mean, Randy and I were already tight, but that was a real
bonding experience for us. And, yeah... I mean, and I learned from that
that it's like I don't look back on that enough actually, because I think we often, at least for me, I don't necessarily have
the confidence to think that things will work out, that I'll be able to get
through a certain thing. But my ability to actually
get something done in that moment is better
than I give myself credit for, I think. And that was the lesson of that story that I really took away. - Well, actually, just for
me, you're making me realize now that it's not just
those kinds of stories, but even things like
periods of depression, or really low points. To me at least it feels
like a motivating thing that the darker it gets,
the better the story will be if you emerge on the other side. That, to me, feels like
a motivating thing. So maybe if people are listening to this and they're going through
some shit, as we said, one thing that could be a source of light is that it'll be a hell of a good story when it's all over, when you
emerge on the other side. Let me ask you about decisions. You've already talked
about it a little bit, but when we face the world and we're making different decisions, how much does our memory come into play? Is it the kind of narratives
that we've constructed about the world that are
used to make predictions that's fundamentally part
of the decision making? - Absolutely, yeah. So let's say after this you and I decided we're gonna go for a beer, right? How do you choose where to go? You're probably gonna be
like, "Oh, yeah, this new bar opened up near me, I
had a great time there, they had a great beer selection." Or you might say, "Oh,
we went to this place and it was totally crowded
and they were playing this horrible EDM or whatever." And so right there, valuable
source of information, right? And then you have these
things like where you do this counterfactual stuff like, "Well I did this previously, but what if I had gone
somewhere else instead? Maybe I'll go to this other place because I didn't try
it the previous time." So there's all that kind of
reasoning that goes into it too. I think even if you think
about the big decisions in life, right? It's like you and I were talking
before we started recording about how I got into memory
research and you got into AI and it's like we all have
these personal reasons that guide us in these
particular directions. And some of it's the environment
and random factors in life and some of it is memories of
things that we wanna overcome, or things that we build
on in a positive way. But either way they define us. - And probably the earlier
in life the memories happen the more defining power they have in terms of determining who we become. - I mean, I do feel like
adolescence is much more important than I think people give credit for. I think that there is this
kind of a sense like, you know, the first three years of life
is the most important part, but the teenage years
are just so important for the brain, you know? And so that's where a
lot of mental illness starts to emerge. You know, now we're thinking
of things like schizophrenia as a neurodevelopmental disorder because it just emerges during that period of adolescence and early adulthood. So... And I think the other part
of it is, is that, you know, as, I guess I was a little
bit too firm in saying that memory determines who we are. It's really the self is
an evolving construct. I think we kind of underestimate that. And when you're a parent
you feel like every decision you make is consequential
in forming this child. And it plays a role, but
so do the child's peers. And so do you know, there's so much... I mean, that's why I think
the big part of education I think that's so important
is not the content you learn. I mean, think of how much dumb
stuff we learned in school. Right? But a lot of it is learning
how to get along with people, and learning who you are,
and how you function. And, you know, that can
be terribly traumatizing even if you have perfect, you
know, parents working on you. - Is there some insight
into the human brain that explains why we
don't seem to remember anything from the first few years of life? - Yeah, yeah. In fact, actually I was just talking to my really good friend and
colleague, Simona Ghetti, who studies the neuroscience
of child development. And so we were talking about this. And so there are a bunch
of reasons I would say. So one reason is, is
there's an area of the brain called the hippocampus,
which is very, very important for remembering events,
or episodic memory. And so the first two years
of life there's a period called infantile amnesia. And then the next couple of years of life after that, there's a period
called childhood amnesia. And the difference is is
that basically in the lab and, you know, even during
childhood and afterwards, children basically don't
have any episodic memories for those first two years. The next two years it's very fragmentary, and that's why they call
it childhood amnesia. So there's some, but it's not much. So one reason is that the
hippocampus is taking some time to develop, but another is the neocortex, so the whole folded stuff
of gray matter all around the hippocampus, is developing so rapidly and changing and a child's
knowledge of the world is just massively being built up, right? So I mean, I'm gonna
probably embarrass myself, but it's like if you showed
like, you know, you trained a neural network and you
give it like the first couple of patterns, or something like
that, and then you bombard it with another like, you
know, years worth of data, try to get back those first
couple of patterns, right? It's like everything changes. And so the brain is so plastic, the cortex is so plastic during that time. And we think that memories for
events are very distributed across the brain. So imagine you're trying to get back that pattern of activity that happened during this one moment, but
the roads that you would take to get there have been
completely rerouted, right? So I think that's my best explanation. The third explanation is
a child's sense of self takes a while to develop. And so their experience of
learning might be more learning what happened as opposed
to having this first person experience of, "I remember, I was there." - Well I think somebody once said to me that, kind of loosely, philosophically, that the reason we don't
remember the first few years of life, infantile amnesia, is
because how traumatic it is. Basically the error
rate that you mentioned, when your brain's prediction
doesn't match reality, the error rate in the
first few years of life, your first few months certainly,
is probably crazy high. It's just nonstop freaking out. The collision between
your model of the world and how the world works is just so high that you want whatever the trauma of that is not to linger around. I always thought that's
an interesting idea because like, just imagine the
insanity of what's happening in a human brain in
the first couple years. Just, you don't know anything, and then there's just
this stream of knowledge and we're somehow, given
how plastic everything is, it just kind of molds and figures it out. But it's like an insane
waterfall of information. - I wouldn't necessarily
describe it as a trauma, and we can get into this
whole stages of life thing, which I just love. Basically those first few
years there are, I mean, you know, I mean think about
it, a kid's internal model of their body is changing, right? It's like just learning to move. I mean like, you know, if you
ever have a baby you'll know that like the first three months they're discovering their toes. Right? It's just nuts. So everything is changing. But what's really fascinating is, and I think this is one of those... This is not at all me being a scientist, but it's like one of those
things that people talk about when they talk about the,
you know, positive aspects of children is that they're
exceptionally curious and they have this kind of
openness towards the world. And so that prediction error is not a negative, traumatic thing. I think it's like a very positive thing because it's what they use,
they're seeking information. One of the areas that I'm very interested in is the prefrontal cortex. It's an area of the brain that... I mean, I could talk all day about it, but it helps us use our knowledge to say, "Hey, this is what I want
to do now, this is my goal, so this is how I'm going to achieve it." And focus everything
towards that goal, right? The prefrontal cortex takes
forever to develop in humans. The connections are still being tweaked and reformed like into late
adolescence, early adulthood, which is when you tend to see
mental illness pop up, right? So it's being massively reformed. Then you have about 10 years,
maybe, of prime functioning of the prefrontal cortex and
then it starts going down again and you end up being older and you start losing all
that frontal function. So I look at this and
you'd say, okay, from... You sit around episodic memory talks, we'll always say children
are worse than adults at episodic memory, older adults
are worse than young adults at episodic memory. And I always would say,
"God, this is so weird, why would we have this period
of time that's so short when we're perfect?" Right? Or optimal. And I like to use the word optimal now because there's such a culture
of optimization right now. And it's like, I realize I have
to redefine what optimal is because for most of the human condition I think we had a series of stages of life where you have basically
adults saying, "Okay," young adults saying, "I've got a child and, you know, I'm part of this village and I have to hunt and
forage and get things done. I need a prefrontal cortex so I can stay focused on the big picture and the long haul goals." Now I'm a child, I'm in this
village, I'm kinda wandering around and I've got some safety and I need to learn about this culture because I know so little. What's the best way to do that? Let's explore. I don't wanna be constrained
by goals as much. I wanna really be free,
play, and explore, and learn. So you don't want a super
tight prefrontal cortex. You don't even know what
the goals should be yet. Right? It's like if you're
trying to design a model that's based on a bad goal, it's not gonna work well, right? So then you go late in life and you say, "Oh, why don't you have a
great prefrontal cortex then?" But I think, I mean if you go back and you think how many
species actually stick around naturally long after
their childbearing years are over, after the
reproductive years are over? Like menopause. From what I understand,
menopause is not all that common in the animal world, right? So why would that happen? And so I saw Alison Gopnik
said something about this, so I started to look into
this, about this idea that, you know, really when
you're older, in most societies, your job is no longer to
form new episodic memories, it's to pass on the memories
that you already have, this knowledge about the world, what we call semantic memory, to pass on that semantic memory
to the younger generations, pass on the culture. You know, even now in indigenous cultures, that's the role of the elders. And they're respected, they're not seen as, you know, people who
are past it and losing it. And I thought that was
a very poignant thing, that memory's doing what it's supposed to throughout these stages of life. - So it is always optimal in a sense. - Yeah.
- It's just optimal for that stage of life. - Yeah, and for the ecology of the system. So you've got... So I looked into this and
it's like another species that has menopause is orcas. Orca pods are led by
the grandmothers, right? So not the young adults,
not the parents or whatever, the grandmothers. And so they're the ones
that pass on the traditions to the, I guess, the
younger generation of orcas. And if you, you know, if you look, from what little I understand, different orca pods have
different traditions, they hunt for different things, they have different play traditions, and that's a culture, right? And so in social animals
evolution, I think, is designing brains that are really around, you know, it's obviously optimized for the individual but also for kin. And I think that the kin are part of this, like when they're a part of
this intense social group, the brain development
should parallel that, the nature of the ecology. - Well it is just fascinating to think of the individual orca, or
human, throughout his life in stages doing a kind of
optimal wisdom development. So in the early days you don't
even know what the goal is, then you figure out the goal and you kind of optimize for that goal and you pursue that goal. And then all the wisdom you collect through that, then you share
with the others in the system, with the other individuals, and as a collective then
you kind of converge towards greater wisdom throughout the generation. So in that sense it's optimal. Us humans and orcas
got something going on. It works.
- Oh, yeah. Apex predators. - I just got a megalodon tooth,
speaking of apex predators. - Oh, man! - It's... Just imagine the size of that thing. Anyway, how does the brain forget and how and why does it remember? So maybe some of the mechanisms? You mentioned the hippocampus, what are the different
components involved here? - So we could think about
this on a number of levels. Maybe I'll give you the
simplest version first, which is we tend to think of memories as these individual things
and we can just access them, maybe a little bit like, you
know, photos on your phone, or something like that. But in the brain, the way it works is you have this distributed pool of neurons and the
memories are kind of shared across different pools of neurons. And so what you have is competition, where sometimes memories
that overlap can be fighting against each other, right? So sometimes we forget because that competition
just wipes things out. Sometimes we forget because there aren't
the biological signals, which we can get into, I would promote long-term retention. And lots of times we forget because we can't find the
cue that sends us back to the right memory. And we need the right cue to
be able to activate it, right? So, you know, for instance,
in a neural network there is no... You wouldn't go and you'd
say, "This is the memory." Right? It's like the whole network,
I mean the whole ecosystem of memories is in the weights
of the neural network. And in fact you could
extract entirely new memories depending on how you feed. - You have to have the right
query, the right prompt, to access that whatever the
part you're looking for. - That's exactly right. That's exactly right. And in humans you have
this more complex set of ways memory works. There's, as I said, the knowledge, or what you call semantic memory, and then there's these
memories for specific events, which we call episodic memory. And so there's different
pieces of the puzzle that require different kinds of cues. So that's a big part of it too, is just this kind of what
we call retrieval failure. - You mentioned episodic memory, you mentioned semantic memory. What are the different separations here? What's what working
memory, short-term memory, long-term memory, what are the interesting
categories of memory? - Yeah. And so memory researchers,
we love to cut things up and say, you know, is memory
one thing or is it two things? Is it two things, or is it three things? And so one of the things that... There's value in that, and
especially experimental value in terms of being able to dissect things. In the real world, it's all connected. Speaking to your question,
working memory is a term that was coined by Alan Baddeley. It's basically thought to be this ability to keep information online in your mind right in front of you at a given time, and to be able to control
the flow of that information, to choose what information is relevant, to be able to manipulate it, and so forth. And one of the things that Alan
did that was quite brilliant was he said, there's this ability
to kind of passively store information, you know, see
things in your mind's eye, or hear your internal monologue. But, you know, we have that ability to keep information in mind, but then we also have this
separate, what he called, a central executive, which is identified a lot
with the prefrontal cortex, it's this ability to control
the flow of information that's being kept active based
on what it is you're doing. Now a lot of my early
work was basically saying that this working memory, which some memory researchers
would call short-term memory, is not at all independent
from long-term memory. That is that a lot of executive
function requires learning and you have to have like synaptic change for that to happen. And... But there's also
transient forms of memory. So one of the things I've
been getting into lately is the idea that we form
internal models of events. The obvious one that I always use is birthday parties, right? So you go to a child's birthday party, once the cake comes out and they start, you just see a candle, you
can predict the whole frame, you know, set of events
that happens later. And up till that point where
the child blows out the candle, you have an internal model in
your head of what's going on. And so if you follow people's eyes, it's not actually on what's happening, it's going where the
action's about to happen. Which is just fascinating, right? So you have this internal model and that's a kind of a
working memory product. It's something that you're keeping online that's allowing you to
interpret this world around you. Now to build that model though
you need to pull out stuff from your general knowledge of the world, which is what we call semantic memory, and then you'd wanna be
able to pull out memories for specific events that
happened in the past, which we call episodic memory. So in a way they're all connected, even though it's different, the things that we're focusing on, and the way we organize
information in the present, which is working memory, will
play a big role in determining how we remember that information later, which people typically
call long-term memory. - So if you have something
like a birthday party, and you've been to many
before, you're gonna load that from disc into
working memory, this model, and then you're mostly
operating on the model. And if it's a new task,
you don't have a model so you're more in the data collection? - Yes. One of the fascinating things
that we've been studying, and this is, we're not at
all the first to do this, Jeff Zacks was a big pioneer in this, and I've been working
with many other people, Ken Norman, Lila Davachi, NY or Columbia, has done some interesting
stuff with this, is this idea that we form these internal
models at particular points of high prediction error, or points of, I believe
also points of uncertainty, points of surprise, or
motivationally significant periods, and those points are when
it's maximally optimal to encode an episodic memory. So I used to think, "Oh,
well we're just encoding episodic memories constantly,
boom, boom, boom, boom, boom." But think about how much redundancy there is in all that, right? It's just a lot of information
that you don't need. But if you capture an episodic memory at the point of maximum uncertainty for the singular experience, right, you're just, it's
only gonna happen once. But if you capture it at the
point of maximum uncertainty, or maximum surprise, you have the most useful
point in your experience that you've grabbed. And what we see is that the hippocampus, and these other networks that are involved in generating these
internal models of events, they show a heightened
period of connectivity, or correlated activity,
during those breaks between different events,
which we call event boundaries. These are the points where
you're like surprised or you cross from one room
to another, and so forth. And that communication is associated with a bump of activity in the hippocampus and better memory. And so if people have a
very good internal model throughout that event you don't need to do much memory processing, you're in a predictive mode, right? And so then at these event
boundaries you encode and then you retrieve and you're like, "Okay, wait a minute,
what's going on here? Ranganath's now talking about orcas. What's going on?" And maybe you have to go back and remember reading my book
to pull out the episodic memory to make sense of whatever it
is I'm babbling about, right? And so there's this beautiful dynamics that you can see in the brain
of these different networks that are coming together
and then deaffiliating at different points in
time that are allowing you to go into these modes. And so to speak to your original
question, to some extent when we're talking about semantic memory, and episodic memory, and working memory, you can think about it as these
processes that are unfolding as these networks kind of
come together and pull apart. - Can memory be trained and improved? This beautiful connected
system that you've described, what aspect of it is a mechanism that can be improved through training? - I think improvement, it
depends on what your definition of optimal is. So what I say in the book
is, is that you don't wanna remember more, you wanna remember better, which means focusing on the
things that are important. And that's what our
brains are designed to do. So if you go back to the
earliest quantitative studies in memory by Ebbinghaus what
you see is that he was trying so hard to memorize
this arbitrary nonsense and within a day he lost
about 60% of that information. And he was using... He was basically using a
very, very generous way of measuring it, right? So as far as we know nobody
has managed to violate those basics of having people forget, you know, most of their experiences. So if your expectation is
that you should remember everything, and that's
what your optimal is, you're already off because
this is not what human brains are designed to do. On the other hand, what
we see over and over again is that the brain does... Basically, one of the cool
things about the design of the brain is it's always less is more. Less is more, right? It's like, I mean I've seen estimates that the human brain uses
something like 12 to 20 watts, you know, in a day. I mean, that's just nuts, the
low power consumption, right? So it's all about reusing information and making the most of
what we already have. And so that's why basically,
again, what you see biologically is, you know, neuromodulators for instance, these chemicals in the brain like norepinephrine, dopamine, serotonin, these are chemicals that are released during moments that tend to
be biologically significant: surprise, fear, stress, et cetera. And so these chemicals promote
lasting plasticity, right? Essentially some mechanisms
for which the brain can say prioritize the information
that you carry with you into the future. Attention is a big factor as well, our ability to focus our
attention on what's important. And so there's different schools of thought on training
attention, for instance. So one of my colleagues, Amishi
Jha, she wrote a book called "Peak Mind" and talks about mindfulness as a method for improving
attention and focus. So she works a lot with military,
like Navy SEALs and stuff, to do this kind of work
with mindfulness meditation. Adam Gazzaley, another one
of my friends and colleagues, his work on kind of
training through video games actually as a way of training attention. And so it's not clear to me,
you know, one of the challenges though in training is you tend to over fit to the thing that you're
trying to optimize, right? So you tend to, if I'm
looking at a video game, I can definitely get
better at paying attention in the context of the video game, but do you transfer it
to the outside world? That's very controversial. - The implication there is
that attention is a fundamental component of remembering something, allocating attention to it, and then attention might be
something that you could train. How you allocate attention and how you hold attention on a thing. - I can say that in fact we
do in certain ways, right? So if you are an expert in something, you are training attention. So we did this one study
of expertise in the brain and, you know, so people used to think, let's say if you're a bird
expert or something, right? People will go, like if you
get really into this world of birds, you start to see the differences in your visual cortex is tuned up and it's all about plasticity
of the visual cortex. And vision researchers love
to say everything's visual, you know, but... But it's like we did
this study of attention and working, or working
memory and expertise and one of the things that surprised us were the biggest effects
as people became experts in identifying these different
kinds of just crazy objects that we made up, as they
developed this expertise of being able to identify
what made them different from each other, and
what made them unique, we were actually seeing
massive increases in activity in the prefrontal cortex. And this fits with some of
the studies of chess experts, and so forth, that it's
not so much that you learn the patterns passively,
you learn what to look for, you learn what's important
and what's not, right? And you can see this
in any kind of expert, professional athlete, they're
looking three steps ahead of where they're supposed to be. So that's a kind of a
training of attention. And those are also what you'd
call expert memory skills. So if you take the memory athletes, I know that's something
we're both interested in. And, you know, so these
are people who train in these competitions and
they'll memorize like a deck of cards in like a really
short amount of time. There's a great memory athlete, her name I think is pronounced
Yanjaa Wintersoul, but she... So I think she's got like a
giant Instagram following. And so she had this YouTube
video that went viral where she had memorized an
entire IKEA catalog, right? And so how do people do this? By all accounts from people
who become memory athletes, they weren't born with
some extraordinary memory, but they practice strategies
over and over and over again. The strategy that they use for memorizing a particular thing, it
can become automatic and you can just deploy
it in an instant, right? So, again, it's not necessarily gonna... One strategy for learning
the order of a deck of cards might not help you for
something else that you need, like, you know, remembering
your way around Austin, Texas, but it's gonna be these,
whatever you're interested in, you can optimize for that. And that's just a natural
byproduct of expertise. - There's certain hacks. There's something called the memory palace that I've played with. I don't know if you're familiar
with that whole technique? And it works. It's interesting. So another thing I
recommend for people a lot is I use Anki a lot every day. It's a app that does space repetition. So I think medical students, and like students use
this a lot to remember a lot of different things. - Oh, yeah. Okay, we can come back
to this, but yeah, go on. - Sure, it's the whole
concept of spaced repetition. You just... When the thing is fresh, you
kind of have to remind yourself of it a lot, and then over
time you can wait a week, a month, a year before you
have to recall the thing again. And that way you essentially
have something like note cards that you can have tens of
thousands of and can only spend 30 minutes a day and
actually be refreshing all of that information,
all of that knowledge. It's really great. And then for memory palace is a technique that allows you to remember
things like the IKEA catalog by placing them visually in a place that you're really familiar with. Like, I'm really familiar
with this place so I can put numbers, or facts, or
whatever you wanna remember. You can walk along that little palace and it reminds you. It's cool. Like there's stuff like
that that I think athletes, memory athletes could use, but I think also regular people can use. One of those things that
I have to solve for myself is how to remember names. I'm horrible at it. - [Charan] Yeah. - I think it's because when
people introduce themselves I have the social anxiety
of the interaction where I'm like, "I know I
should be remembering that," but I'm freaking out internally about social interaction in general and so therefore I forget immediately. So I'm looking for good tricks for that. - So I feel like we've
got a lot in common, because when people
introduce themselves to me it's almost like I have this
like just blank blackout for a moment and then
I'm just looking at them like, "What happened?" And I look away or something. What's wrong with me? - Yeah. - So, I mean, I'm
totally with you on this. The reason why it's hard
is that there's no reason we should be able to remember names, because when you say remembering a name, you're not really remembering a name. Maybe in my case you
are, but most of the time you're associating a name
with a face and an identity. And that's a completely
arbitrary thing, right? I mean, maybe in the olden
days somebody named Miller, it's like they're actually making flour or something like that. But, you know, for the most
part it's like these names are just utterly arbitrary, so you have no thing to latch onto. And so it's not really a thing that our brain does very well is to learn meaningless, arbitrary stuff. So what you need to do is
build connection somehow. Visualize a connection. And sometimes it's obvious,
or sometimes it's not. I'm trying to think of
a good one for you now, but the first thing I
think of is Lex Luthor. But-
- That's great. - Yeah.
- 'Cause doesn't Lex Luthor wear a suit, I think? - I know he has a shaved head though. - Yeah.
- Or he's bald, which you're not. You've got a great head of... I'd trade hair with you any day, but- - Right. - But like, you know, something like that. But if I can come up with something. Like, I could say, "Okay, so Lex Luthor is this criminal mastermind." Then I just imagine you- - We talked about stabbing
or whatever earlier- - Yeah, yeah, exactly. - So just gotta connect it and that's it. - Yeah, yeah. And I... But I'm serious though that these kinds of weird associations, now I'm building a richer network. I mean, one of the things
that I find is if I've... Like you can have somebody's name that's just totally generic,
like John Smith or something. Not that... No offense to people with that name. But, you know, if I see a generic name like that, but I've read John
Smith's papers academically and then I meet John
Smith at a conference, I can immediately associate
that name with that face, 'cause I have this preexisting network to lock everything into, right? And so you can build that network, and that's what the method of loci, or the memory palace
technique is all about, is you have a preexisting
structure in your head of like your childhood home, or this mental palace that
you've created for yourself, and so now you can put arbitrary pieces of information in different locations in that mental structure of yours, and then you could walk
through the different path and find all the pieces of
information you're looking for. So the method of loci is a great method for just learning arbitrary things because it allows you
to link them together and get that cue that you need to pop in and find everything, right? - We should maybe linger
on this memory palace thing just to make obvious. 'Cause when people were
describing to me a while ago what this is, it seems insane. I just, you literally think of a place like a childhood home, or a home that you're
really visually familiar with, and you literally place in that three dimensional
space facts, or people, or whatever you wanna remember. And you just walk in your mind
along that place visually, and you can remember, remind yourself of the different things. One of the limitations is
there is a sequence to it. So I think your brain somehow, you need, you can't just like go upstairs
right away or something, you have to like walk along the room. So it's really great for
remembering sequences, but it's also not great for remembering like individual
facts out of context. So the full context of the
tour I think is important. But it's fascinating how the mind is able to do that when you ground these pieces of knowledge into something that you remember well
already, especially visually. Fascinating. And you could just do that
for any kind of sequence. And I'm sure she used something like this for the, for IKEA catalog,
something of this nature. - Oh, yeah, absolutely. Absolutely. And I think the principle here
is, again, I was telling you this idea that memories can
compete with each other, right? Well, I like to use this example, and maybe someday I'll regret this, but I've used it a lot recently, is like imagine if this were
my desk it could be cluttered with a zillion different things, right? So imagine it's just
cluttered with a whole bunch of yellow post-it notes and on one of them I put my
bank password on it, right? Well it's gonna take
me forever to find it. I might, you know, it's
just gonna be buried under all these other post-it notes. But if it's like hot
pink it's gonna stand out and I find it really easily, right? So that's one way in which
if things are distinctive, if you've processed information
in a very distinctive way, then you can have a
memory that's gonna last. And that's very good, for instance, for name-face association. So if I get something
distinctive about you, you know that it's like that
you've got very short hair and maybe I can make the
association with Lex Luthor that way, or something like that, right? You know? But I get something very specific. That's a great cue. But the other part of it
is, what if I just organized my notes so that I have
my finances in one pile and I have my like reminders, my to-do list in one pile, and so forth. And so I organize them. Well then I know exactly if
I'm going for my banking, you know, my bank password, I could go to the finance pile, right? So the method of loci works,
or memory palaces work because they give you a way of organizing. There's a school of thought
that says that episodic memory evolved from this like kind of knowledge of space and, you know, basically
this primitive abilities to figure out where you are, and so people explain the
method of loci that way. And, you know, whether or
not the evolutionary argument is true, the method of
loci is not at all special. So if you don't, you're
not a good visualizer, stories are a good one. So a lot of memory
athletes will use stories and they'll go... Like if you're memorizing a deck of cards, they have a little code for the different, like the king and the jack
and the 10 and so forth. And they'll make up a story about things that they're doing, and that'll work. Songs are a great one, right? I mean, it's like, I can still
remember there's this obscure episode of the TV show, "Cheers." They sing a song about Albania
that he uses to memorize all these facts about Albania, and I could still sing that song to you. It's... It is just, I saw it
on a TV show, you know. - So you mentioned spaced repetition, so do you like this process? Maybe can you explain it? - Oh, yeah. If I am trying to memorize something, let's say if I have an hour to memorize as many Spanish words as I can, if I just try to do like half an hour and then later in the
day I do half an hour, I won't retain that information as long as if I do half an hour today and half an hour one week from now. And so doing that extra
spacing should help me retain the information better. Now there's a interesting
boundary condition which is, it depends on when
you need that information. So many of us, you know, for
me, like I can't remember so much from college and
high school 'cause I crammed, 'cause I just did everything
at the last minute. And sometimes I would literally study like, you know, in the
hallway right before the test. And that was great
because what would happen is, is I just had that
information right there. And so actually not
spacing can really help you if you need it very quickly, right? But the problem is, is that
you tend to forget it later on. But on the other hand,
if you space things out, you get a benefit for later on retention. And so there's many
different explanations. We have a computational model of this, it's currently under revision. But in our computer model, what
we say is, is that an easy, maybe a good way of thinking
about this is this conversation that you and I are having, it's associated with a particular context,
a particular place in time. And so all these little cues
that are in the background, these little guitar
sculptures that you have, and that big light umbrella thing, right? All these things are part of my memory for what we're talking about, the content. So now later on you're sitting around and you're at home drinking a beer and you're thinking, "God, what a strange interview that was." Right? So now you're trying to remember it, but the context is different. So your current situation doesn't match up with the memory that you pulled up. There's error. There's a mismatch between
what you've pulled up and your current context. And so in our model, what
you start to do is you start to erase or alter the parts of the memory that are associated with
a specific place and time, and you heighten the
information about the content. And so if you remember this
information in different times, in different places, it's more accessible at different times in different places, because it's not overfitted, in a AI kind of way of
thinking about things, not overfitted to one particular context. But that's also why the memories
that we call upon the most also feel kind of like they're just things that we read about almost, you don't vividly reimagine them, right? It's like they're just these
things that just come to us, like facts, right? - [Lex] Yeah. - And it's a little bit
different than semantic memory, but it's like basically these
events that we have recalled every, you know, over
and over and over again, we keep updating that memory
so it's less and less tied to the original experience. But then we have those other ones, which it's like you just get a reminder of that very specific context. You smell something, you
hear a song, you see a place that you haven't been to in a while and boom, it just comes back to you. And that's the exact opposite
of what you get with spacing. Right? - That's so fascinating. So with spaced repetition,
one of its powers is that you lose attachment
to a particular context, but then it loses the intensity
of the flavor of the memory. - Mm-hmm.
- That's interesting. That's so interesting. - Yeah. But, you know, at the same
time it becomes stronger in the sense that the
content becomes stronger. - Yeah, so it's used
for learning languages, for learning facts, for learning, for... But, you know, for that generic semantic information type of memories. - Yeah. And I think this falls into a category, we've done other modeling, one of these is a published study in "PLOS Computational Biology," where we show that another
way, which is I think related to the spacing effect, is what's
called the testing effect. So the idea is, is that if
you're trying to learn words, let's say in Spanish,
or something like that, and this doesn't have to be
words, it could be anything, you test yourself on the words and that act of testing yourself
helps you retain it better over time than if you just studied it. Right? And so from traditional learning theories, some learning theories,
anyway, this seems weird, why would you do better, giving
yourself this extra error from testing yourself
rather than just, you know, giving yourself perfect input that's a replica of what it is
that you're trying to learn? And I think the reason is, is
that you get better retention from that error, that mismatch
that we talked about, right? So what's happening in our model, it's actually conceptually
kind of similar to what happens with back prop in AI, or neural networks. And so the idea is, is that you expose, "Here's the bad connections, and here's the good connections." And so we can keep the
parts of the cell assembly that are good for the memory and lose the ones that are not so good. But if you don't stress test the memory, you haven't exposed it to the error fully. And so that's why I think this
is kind of, this is a thing that I come back to over and over again, is that you will retain information better if you're constantly pushing
yourself to your limit, right? If you are feeling like you're coasting, then you're actually not learning. So if it's like- - Always, so you should
always be stress testing the memory system? - Yeah, and feel good about it. You know, even though everyone tells me, "Oh, my memory's terrible." In the moment they're overconfident about what they'll retain later on. So it's fascinating. And so what happens is,
is when you test yourself, you're like, "Oh my God,
I thought I knew that, but I don't." And so it can be demoralizing until you get around that and you realize, "Hey, this is the way that I learn. This is how I learn best." It's like if you're trying
to, you know, star in a movie or something like that, you
don't just sit around reading the script, you actually act it out and you're gonna botch those
lines from time to time. Right? - You know, there's an interesting moment. You probably have experienced this. I remember a good friend
of mine, Joe Rogan, I was on his podcast and
we were randomly talking about soccer, football. Somebody I grew up watching,
Diego Armando Maradona, one of the greatest soccer
players of all time. And we were talking about
him and his career and so on. And Joe asked me if he's still around. Now... And I said, "Yeah." I don't know why I thought, "Yeah." Because that was a perfect
example of memories. He passed away. I tweeted about it, how heartbroken I was, all this kind of stuff,
like a year before. I know this but in my mind I went back to the thing I've done
many times in my head, visualizing some of the epic
runs he had on goal, and so on. So for me, he's alive. And so I'm... In part of also the
conversation when you're talking to Joey there's stress and like... The focus is allocated,
the attention is allocated in a particular way. But when I walked away I was like, "In which world was Diego
Maradona still alive?" Like in which... 'Cause I was sure- - Yeah.
- In my head that he was still alive. And it was a... It's a moment that sticks with me. I've had a few like that in my life where it just kinda... Like obvious things just
disappear from mind. And it's cool. Like it shows actually
the power of the mind, in a positive sense, to erase memories you want erased maybe. But I don't know. I don't know if there's a
good explanation for that. - One of the cool things that I found is that some people really
just revolutionize a field by creating a problem
that didn't exist before. It's kinda like why I love science, it's like engineering is like solving other people's problems, and science is about creating problems. And I'm just much more
like I want to break things and, you know, create problems. - [Lex] Yeah. - Not necessarily move fast though. But one of my former
mentors, Marcia Johnson, who in my opinion is one of
the greatest memory researchers of all time, she comes up,
young woman in the field, and it's mostly guy field, and she gets into this idea of
how do we tell the difference between things that we've imagined and things that we actually remember. How do we tell... I get some mental experience, where did that mental
experience come from? Right? And it turns out this is a huge problem because essentially our mental experience of remembering something that happened, our mental experience of
thinking about something, how do you tell the difference? They're both largely
constructions in our head. And so it is very important. And the way that you do it is... I mean, it's not perfect,
but the way that we often do it and succeed is by, again,
using our prefrontal cortex and really focusing on
the sensory information or the place and time and
the things that put us back into when this information happened. And if it's something you thought about you're not gonna have
all of that vivid detail as you do for something
that actually happened. But it doesn't work all the time. But that's a big thing
that you have to do. But it takes time. It's slow and it's, again, effortful. But that's what you need
to remember accurately. But what's cool, and I think
this is what you alluded to about how that was an
interesting experience, is imagination's exactly the opposite. Imagination is basically saying, "I'm just gonna take all
this information from memory, recombine it in different
ways and throw it out there." And so for instance, Dan
Schacter and Donna Addis have done cool work on this. Demis Hassabis did work on this with Eleanor Maguire and UCL. And this goes back actually
to this guy Frederic Bartlett who is this revolutionary
memory researcher. Bartlett, he actually like
rejected the whole idea of quantifying memory. He said, there's no statistics in my book. He came from this
anthropology perspective. And, short version of the
story is, he just asked people to recall things. You give people stories and
poem, ask people to recall them. And what he found was people's
memories didn't reflect all of the details of
what they were exposed to. And they did reflect a lot more, they were filtered through
this lens of prior knowledge, the cultures that they came
from, the beliefs that they had, the things they knew. And so what he concluded was
that he called remembering an imaginative construction, meaning that we don't replay the past, we imagine how the past could have been by taking bits and pieces
that come up in our heads. And, likewise, he wrote this
beautiful paper on imagination saying, when we imagine
something, and create something, we're creating it from
these specific experiences that we've had and combining
it with our general knowledge. But instead of trying to
focus it on being accurate and getting out one thing you're
just ruthlessly recombining things without any,
you know, any necessary kind of goal in mind. I mean, or at least that's
one kind of creation. - So imagination is
fundamentally coupled with memory in both directions? - I think so. I mean, it's not clear
that it is in everyone, but one of the things that's
been studied is some patients who have amnesia, for instance,
they have brain damage say to the hippocampus and
if you ask them to imagine things that are not in front of them, like imagine what could happen
after I leave this room. Right? They find it very difficult
to give you a scenario what could happen. Or if they do it would
be more stereotype like, "Yes, this would happen, this would..." But it's not like they can come up with anything that's very vivid
and creative in that sense. And it's partly 'cause
when you have amnesia, you're stuck in the present. Because to get a very
good model of the future it really helps to have
episodic memories to draw upon. Right? And so that's the basic idea. And in fact one of the most
impressive things when people started to scan people's brains and ask people to remember past events, what they found was there
was this big network of the brain called the
default mode network. It gets a lot of press because it's like thought to be important, it's engaged during mind wandering. And if I ask you to pay
attention to something, it only comes on when you
stop paying attention. You know, so people, "Oh, it's just this kind of,
you know, daydreaming network." And I thought, this is
just ridiculous research. Who cares? You know? But then what people found
was when people recall episodic memories, this
network gets active. And so we started to look
into it and this network of areas is really closely
functionally interacting with the hippocampus. And so... In fact, some would say the hippocampus is part of this default network. And if you look at brain images of people, or brain maps of activation, so to speak, of people imagining possible scenarios of things that could happen in the future, or even things that couldn't
really be very plausible, they look very similar. I mean, you know, to the naked
eye they look almost the same as maps of brain activation
when people remember the past. According to our theory,
and we've got some data to support this, we've
broken up this network in various sub pieces, is that basically it's
kind of taking apart all of our experiences and
creating these little Lego blocks out of them, and then you
can put them back together if you have the right
instructions to recreate these experiences that you've had, but you could also reassemble
them into new pieces to create a model of an event
that hasn't happened yet. And that's what we think happens. And when I'm... Our common ground that we're
establishing in language requires using those building blocks to put together a model
of what's going on. - Well there's a good percentage of time I personally live in the imagined world. I think of... I have... I do thought experiments a lot. I, you know, take the
absurdity of human life as it stands and play it forward in all kinds of different directions. Sometimes it's rigorous
thought experiments, sometimes it's fun ones. So I imagine that that has an effect on how I remember things. And I suppose I have to
be a little bit careful to make sure stuff happened versus stuff that I
just imagined happened. And this also, I mean,
some of my best friends are characters inside books
that never even existed. And I'm, you know, there's some degree to which they actually exist in my mind. Like these characters
exist, authors exist, Dostoevsky exists, but
also "Brothers Karamazov." - I love that book. - Yeah.
- It's one of the few books I've read. (both laughing) One of the few literature
books that I've read, I should say. I read a lot in school
that I don't remember, but "Brothers Karamazov" was good. - But they exist. - They exist, and I have almost kind of like conversations with them. It's interesting. It's interesting to allow your brain to kind of play with ideas of the past, of the imagined, and see it all as one. - Yeah, there was actually
this famous mnemonist, he is kind of like back
then the equivalent of a memory athlete, except he would go to shows and do this. That was described by this
really famous neuropsychologist from Russia named Luria. And so this guy was named
Solomon Shereshevsky and he had this condition
called synesthesia that basically created
these weird associations between different senses that
normally wouldn't go together. So that gave him this
incredibly vivid imagination that he would use to basically imagine all sorts of things that
he would need to memorize. And he would just
imagine, like just create these incredibly detailed
things in his head that allowed him to
memorize all sorts of stuff. But it also really haunted
him, by some reports, that basically it was
like he was at some point, you know, and again who knows
the drinking was part of this, but at some point had
trouble differentiating his imagination from reality. Right? And this is interesting
because it's like... I mean that's what
psychosis is in some ways, is you, you know, first of
all you're just learning connections from prediction errors that you probably shouldn't learn. And the other part of it is,
is that your internal signals are being confused with actual
things in the outside world. Right? - Well that's why a lot of this stuff is both feature and bug. It's a double-edged sword. - Yeah, I mean it might be why
there's such an interesting relationship between genius and psychosis. - Yeah, maybe they're just
two sides of the same coin. Humans are fascinating, aren't they? - I think so. Sometimes scary, but mostly fascinating. - Can we just talk about
memory sport a little longer? There's something called
the USA Memory Championship. - [Charan] Mm. - Like what are these athletes... Like what does it mean to
be like elite level at this? Have you interacted with any of them? Or reading about them
what have you learned about these folks? - There's a guy named Henry Roediger who's studying these guys. And there's actually a book by Joshua Foer called
"Moonwalking with Einstein," where he talks about... He actually, as part of
this book, just decided to become a memory athlete. They often have these life events that make them go, "Hey,
why don't I do this?" So there was a guy named Scott
Hagwood, who I write about, who thought that he was... He was getting chemo for
cancer and so he decided like, because the chemo,
there's a well-known thing called chemo brain where people
become like, they just lose a lot of their sharpness. And so he wanted to fight that by learning these memory skills. So he bought a book, and
this is the story you hear in a lot of memory
athletes is they buy a book by other memory athletes. - Yeah.
- Or other memory experts, so to speak, and they
just learn those skills and practice them over and over again. They start by winning bets and so forth, and then they go into these competitions. And the competitions are
typically things like memorizing long strings of numbers, or
memorizing, you know, orders of cards and so forth. So there tend to be pretty
arbitrary things, not like things that would be able, you'd be able to bring a lot of prior knowledge. But they build the skills that you need to memorize arbitrary things. - Yeah, that's fascinating. I've gotten a chance to work with something called N-Back tasks. So there's all these kinds of tasks- - [Charan] Oh, yeah. - Memory recall tasks that are used to kinda load up the quote
unquote working memory. - [Charan] Yeah, yeah. - And to see a psychologist
used it to test all kinds of stuff, like to see how well you're good at multitasking. We used it in particular
for the task of driving. Like if we fill up your brain
with intensive working memory tasks, how good are you
at also not crashing? That kind of stuff. So it's fascinating. But, again, those tasks are arbitrary and they're usually about
recalling a sequence of numbers in some kind
of semi complex way. Are you, do you have any favorite tasks of this nature in your own studies? - I've really been most excited about going in the opposite direction and using things that are
more and more naturalistic. - [Lex] Mm. - And the reason is is
that we've really moved in that direction because what we found is, is that memory works
very, very differently when you study it, when
you study memory in the way that people typically remember. And so it goes into a
much more predictive mode and you have these event
boundaries, for instance, and you have... But a lot of what happens is
this kind of fascinating mix that we've been talking about, a mix of interpretations and
imagination with perception. And so... And the new direction we're
going in is understanding navigation in our memory for places. And the reason is, is
that there's a lot of work that's done in rats,
which is very good work. They have a rat and they put it in a box and the rat goes, chases cheese in a box and you'll find cells in the hippocampus that fire when a rat is in
different places in the box. And so the conventional wisdom
is that the hippocampus forms this map of the box. And I think that probably may happen when you have like absolutely
no knowledge of the world. Right? But I think one of the cool
things about human memory is we can bring to bear
our past experiences to economically learn new ones. And so, for instance, if
you learn a map of an IKEA, let's say if I go to the IKEA in Austin, I'm sure there's one here, I
probably could go to this IKEA and find my way to the, you
know, where the wine glasses are without having to even think about it because it's got a very similar layout. Even though IKEA's a
nightmare to get around once I learned my local IKEA,
I can use that map everywhere. Why form a brand new one for a new place? And so that kind of ability
to reuse information really comes into play when we look at things that are, you know,
more naturalistic tasks. And another thing that
we're really interested in is this idea of like what if instead of basically mapping out
every coordinate in a space you form a pretty economical graph that connects basically the
major landmarks together and being able to use that
as, you know, emphasizing the things that are most important, the places that you go for food, and the places that are landmarks
that help you get around, and then filling in the
blanks for the rest. Because I really believe
that cognitive maps, or mental maps, of the world, just like our memories for events, are not photographic. I think they're this combination of actual verifiable details and then a lot of inference that you make. - So what have you learned about this kind of
spatial mapping of places? How do people represent locations? - There's a lot of variability. I think that... And there's a lot of disagreement about how people represent locations. In a world of GPS and
physical maps people can learn it from like basically what
they call a survey perspective, being able to see everything. And so that's one way in
which humans can do it that's a little bit different. There's one way which
we can memorize routes. Like I know how to get from here to... Let's say if I knew... Walk here from my hotel, I
could just rigidly follow that route back, right? And there's another more integrative way which would be what's
called a cognitive map, which would be kind of a sense
of how everything relates to each other. And so there's lots of people
who believe that these maps that we have in our head are
isomorphic with the world that are like these literal coordinates that follow Euclidean space. And as you know, Euclidean
mathematics is very constrained. Right? And I think that we are
actually much more generative in our maps of space so that we do have these bits and pieces. And we've got a small task as... It's right now, not yet... Like we need to do some work
on it for further analyses but one of the things we're looking at is these signals called
ripples in the hippocampus, which are these bursts
of activity that you see that are synchronized with
areas in the neocortex, in the default network actually. And so what we find is,
is that those ripples seem to increase at
navigationally important points when you're making a decision,
or when you reach a goal. This speaks to the emotion thing, right? Because if you have limited choices, if I'm walking down a street I could really just get a
mental map of the neighborhood with a more minimal kind
of thing by just saying, "Here's the intersections and
here's the directions I take to get in between them." And what we found in
general in our MRI studies is basically the more people
can reduce the problem, whether it's space, or any kind
of decision making problem, the less the hippocampus encodes. It really is very economical
towards the points of most highest information
content and value. - So can you describe the
encoding, and the hippocampus, and the ripples you were talking about? What's the signal in
which we see the ripples? - Yeah, so this is really interesting. There are these oscillations, right? So there's these waves
that you basically see and these waves are points
of very high excitability and low excitability. And, at least during... They happen actually
during slow wave sleep too. So the deepest stages of sleep
when you're just zonked out. Right? You see these very slow waves
where it's like very excitable and then very unexcitable. It goes up and down. And on top of them you'll see these little sharp wave ripples. And when there's a
ripple in the hippocampus you tend to see a sequence
of cells that resemble a sequence of cells that
fire when, you know, an animal's actually doing
something in the world. So it almost is like a little... People call it replay. I think it's a little bit,
I don't like that term, but it's basically a little
bit of a compressed play of the sequence of activity in the brain that was taking place earlier. And during those moments
there's a little window of communication between the hippocampus and these areas in the neocortex. And so that, I think, helps
you form new memories, but it also helps you,
I think, stabilize them but also really connect different
things together in memory and allows you to build bridges
between different events that you've had. And so this is one of
our theories of sleep and its real role in helping
you see the connections between different events
that you've experienced. - Oh, so during sleep is when
the connections are formed? - The connections
between different events. - Yeah.
- Right? So it's like you see me
now, you see me next week, you see me a month
later, you start to build a little internal model of how I behave and, you know, what to expect of me. And we think sleep, one of
the things it allows you to do is figure out those connections,
and connect the dots, and find the signal in the noise. - So you mentioned FMRI, what is it and how is it used in studying memory? - This is actually the reason why I got into this whole field of science is when I was in grad school FMRI was just really taking off as a technique for studying brain activity. And what's beautiful
about it is you can study the whole human brain and,
there's lots of limits to it, but you can basically do it in a person without sticking anything
into their brains. And very non-invasive. I mean for me being in an MRI scanner is like being in the
womb, I just fall asleep. If I'm not being asked to do
anything I get very sleepy. You know? But you can have people watch movies while they're being scanned, or you can have them do tests of memory, like giving them words
and so forth to memorize. But what MRI is itself
is just this technique where you put people in a
very high magnetic field. Typical ones we would
use would be 3 Tesla, to give you an idea. So a 3 Tesla magnet, you put
somebody in and what happens is you get this very weak but, you know, measurable
magnetization in the brain and then you apply a
radio frequency pulse, which is basically a different
electromagnetic field. And so you're basically using water, the water molecules in the
brain, as a tracer, so to speak. And part of it in FMRI is the fact that these magnetic fields that you mess with by manipulating these
radio frequency pulses, and the static field, and you
have things called gradients which change the strength
of the magnetic field in different parts of the head. So they're all... We tweak them in different ways, but the basic idea that we use an FMRI is that blood is flowing to the brain and when you have blood
that doesn't have oxygen on it, it's a little bit more magnetizable than blood that does. 'Cause you have hemoglobin
that carries the oxygen, the iron, basically, in the
blood that makes it red. And so that hemoglobin,
when it's deoxygenated, actually has different
magnetic field properties than when it has oxygen. And it turns out when you have
an increase in local activity in some part of the brain
the blood flows there and as a result you get
a lower concentration of hemoglobin that is not oxygenated and then that gives you more signal. So I gave you a... I think I sent you a
GIF, as you like to say. - Yeah, we had off record intense argument about if it's pronounced
GIF or GIF, but that's... We shall set that aside as friends. - We could have called it a
stern rebuke perhaps, but... - Rebuke, yeah. I drew a hard line. It is true the creator of
GIF said it's pronounced GIF, but that's the only person
that pronounces it GIF. Anyway, yes, you sent a GIF of... - This would be basically a
whole a movie of FMRI data. And so when you look at it,
it's not very impressive, it looks like these like very
pixelated maps of the brain, but it's mostly kinda like white. But these tiny changes in the
intensity of those signals, that you probably wouldn't
be able to visually perceive, like about 1% can be statistically very, very large effects for us. And that allows us to see,
"Hey, there's an increase in activity in some part of the brain when I'm doing some task, like trying to remember something." And I can use those
changes to even predict, "Is a person going to
remember this later or not?" And the coolest thing that
people have done is to decode what people are remembering
from the patterns of activity from, 'cause
maybe when I'm remembering this thing, like I'm remembering
the house where I grew up, I might have one pixel that's
bright in the hippocampus and one that's dark, and if I'm remembering, you
know, something more like the car that I used to
drive when I was 16, I might see the opposite pattern, where a different pixel's bright. And so all that little stuff
that we used to think of noise, we can now think of almost like a QR code for memory, so to speak. Where different memories have
a different little pattern of bright pixels and dark pixels. And so this really
revolutionized my research. So there's fancy research out
there where people really... I mean not even that, I
mean by your standards this would be stone age, but, you know, applying
machine learning techniques to do decoding and so forth. And now there's a lot of
forward encoding models and you can go to town
with this stuff, right? And I'm much more old school,
of designing experiments where you basically say,
"Okay, here's a whole web of memories that overlap
in some way, shape or form. Do memories that occurred
in the same place, have a similar QR code? And do memories that
occurred in different places have a different QR code?" And you can just use things
like correlation coefficients or cosign distance to
measure that stuff, right? Super simple, right? And so what happens is
you can start to get a whole state space of how a brain area is indexing all these different memories. It's super fascinating because what we could see is
this little like separation between how certain brain
areas are processing memory for who was there, and other brain areas of processing information
about where it occurred, or the situation that's kind of unfolding. And some are giving you
information about what are my goals that are involved and so forth. And so... And the hippocampus is just
putting it all together into these unique things
that just are about when and where it happened. - So there's a separation
between spatial information concepts, like literally there's distinct, as you said, QR codes for these? - So to speak. Let me try a different analogy too, that might be more accessible for people, which would be like, you've got a folder on your computer, right? I open it up, there's
a bunch of files there. I can sort those files by,
you know, alphabetical order. And now things that
both start with letter A are lumped together, and things that start with Z
versus A are far apart, right? And so that is one way
of organizing the folder. But I could do it by date, and if I do it by date
things that were created close together in time are close and things that are far
apart in time are far. So every... Like you can think of how a brain area, or a network of areas,
contributes to memory by looking at what the sorting scheme is. And these QR codes that
we're talking about, that you get from FMRI,
allow you to do that. And you can do the same
thing if you're recording from massive populations
of neurons in an animal and you can do it for
recording local potentials in the brain. You know, so little waves
of activity in, let's say, a human who has epilepsy and they stick electrodes in their brain, try to find the seizures. So that's some of the
work that we're doing now. But all these techniques
basically allow you to say, "Hey, what's the sorting scheme?" And so we've found that
some networks of the brain sort information in memory
according to who was there. So I might have... Like we've actually shown in
one of my favorite studies of all time that was done by
a former postdoc, Zach Raya, and Zach did the study
where we had a bunch of movies with different people in my labs that are two different people, and you filmed them at two different cafes and two different supermarkets. And what you could show is
in one particular network you could find the same
kind of pattern of activity, more or less, a very, very
similar pattern of activity, every time I saw Alex
in one of these movies, no matter where he was, right? And I could see another one
that was like a common pattern that happened every time I saw this particular supermarket
nugget, you know? And so... And it didn't matter whether
you're watching a movie or whether you're recalling the movie, it was the same kind of
pattern that comes up, right? - That's so fascinating.
- It was fascinating. And so now you have those building blocks for assembling a model of
what's happening in the present, imagining what could happen and remembering things very economically from putting together all these pieces so that all the hippocampus has to do is get the right kind of blueprint for how to put together
all these building blocks. - These are all like beautiful
hints at a super interesting system that makes me
wonder on the other side of it how to build it. But it's like, it's fascinating. Like the way it does the encoding is really, really fascinating. Or I guess the symptoms,
the results of that encoding are fascinating to study from this. Just as a small tangent, you mentioned sort of the measuring local potentials with electrodes versus FMRI. - [Charan] Oh, yeah. - What are some interesting
like limitations, possibilities of FMRI? Maybe... The way you explain it is like brilliant, with blood and detecting the activations, or the excitation, because
blood flows to that area. What's like the latency of that? Like what's the blood
dynamics in the brain that... - [Charan] Yeah, yeah. - Like how quickly can it... How quickly can the tasks change
and all that kind of stuff? - Yeah, I mean it's very slow. To the brain 50 milliseconds
is like, you know, like it's an eternity. Like maybe not 50, but, you
know, maybe like, you know, let's say half a second, 500 milliseconds, just so much back and forth
stuff happens in the brain in that time, right? So in FMRI you can measure
these magnetic field responses about six seconds after
that burst of activity would take place. All these things, it's like,
is it a feature or is it a bug? Right? So one of the interesting
things that's been discovered about FMRI is it's not so
tightly related to the spiking of the neurons. So we tend to think of the
computation, so to speak, as being driven by spikes. Meaning like there's just a burst of, it's either on or it's off, and the neurons like going up or down. But sometimes what you
can have is these states where the neuron becomes a
little bit more excitable or less excitable. And so FMRI is very sensitive to those changes in excitability. Actually one of the
fascinating things about FMRI is where does that... How is it we go from neural activity to, you know, essentially
blood flow to oxygen? You know, all this stuff. It's such a long chain of, you know, going from neural activity to magnetic fields. And one of the theories that's out there is, you know, most of
the cells in the brain are not neurons, they're
actually these support cells called glial cells, and
one big one is astrocytes, and they play this big role in regulating, you know, kind of being a
middle man, so to speak, with the neurons. So if you, for instance,
like one neuron's talking to another, you release a neurotransmitter like let's say glutamate, and that gets another
neuron starts getting active after you release in the gap between the two neurons
called the synapse. So what's interesting is if
you leave that, you know, imagine you're just flooded
with this like liquid in there, right? If you leave it in there too long you just excite the other neuron too much and you can start to basically
get seizure activity. You don't want this. So you gotta suck it up. And so actually what
happens is these astrocytes, one of their functions is
to suck up the glutamate from the synapse and
that is a massively... And then break it down,
and then feed it back into the neurons so that you can reuse it. But that cycling is actually
very energy intensive. And what's interesting is, at
least according to one theory, they need to work so
quickly that they're working on metabolizing the glucose that comes in without using oxygen. Kind of like anaerobic metabolism. So they're not using oxygen as fast as they are using glucose. So what we're really seeing
in some ways maybe, in FMRI, not the neurons themselves being active but rather the astrocytes
which are meeting the metabolic demands of the process of
keeping the whole system going. - It does seem to be
that FMRI is a good way to study activation. So with these astrocytes,
even though there's a latency, it's pretty reliably
coupled to the activations. - Oh, well this gets me to
the other part about my- - [Lex] Yeah. - So now let's say for instance, if I'm just kind of
like I'm talking to you, but I'm kind of paying attention
to your cowboy hat, right? So I'm looking off to the... Or I'm thinking about the right, even if I'm not looking at it. What you'd see is, is that there would be this little elevation in activity in areas in the visual cortex, you know, which process vision,
around that point in space. Okay? So if then something happened, like, you know, a sudden a light flashed in that part of, you know, right in front of your cowboy hat, I would
have a bigger response to it. But what you see in
FMRI is even if I'm not, even if I don't see that flash of light, there's a lot of activity
that I can measure because you're kind of
keeping it excitable. And that in and of itself,
even though I'm not seeing anything there that's
particularly interesting there's still this increase in activity. And so it's more sensitive with FMRI. So there... Is that a feature or is it a bug? You know, some people, people
who study spikes in neurons would say, "Well that's
terrible, we don't want that." You know, likewise it's
slow, and that's terrible for measuring things that are very fast. But one of the things
that we found in our work was when we give people movies and when we give people
stories to listen to a lot of the action is in
the very, very slow stuff. Because if you're thinking
about like a story, let's say you're listening
to a podcast or something, you're listening to the "Lex
Fridman Podcast," right? You're putting this stuff together and building this internal
model over several seconds, which is basically we
filter that out when we look at electrical activity in the brain, because we're interested
in this millisecond scale. It's almost massive amounts
of information, right? So the way I see it is every technique gives you a little limited
window into what's going on. FMRI has huge problems. You know, people lie down in the scanner, there's parts of the brain where you... I'll show you in some of
these images where you'll see kind of gaping holes because there's... You can't keep the magnetic
field stable in those spots. You'll see parts where
it's like there's a vein and so it just produces big increases and decreases in signal. Or respiration that causes these changes. There's lots of artifacts
and stuff like that. You know, every technique has its limits. If I'm lying down in an MRI
scanner, I'm lying down, I'm not interacting
with you in the same way that I would in the real world. But at the same time I'm getting data that I might not be able to get otherwise. And so different techniques give you different kinds of advantages. - What kind of big scientific
discoveries, maybe the flavor of discoveries, have been
done throughout the history of the science of memory,
the studying of memory? What kind of things have
been like understood? - Oh, there's so many. It's really so hard to summarize it. I mean I think it's funny because it's like when you're in the field you can get kind of
blase about this stuff. But then once I started to
write the book I was like, "Oh my God, this is really interesting. How did we do all this stuff?" I would say that some of the... I mean, you know, from the
first studies just showing how much we forget is very important. Showing how much schemas, which
is our organized knowledge about the world, increase our ability to remember information. Just massively increases it. Our studies of expertise,
showing how experts like chess experts can memorize so much in such a short amount of time because of the schemas
they have for chess. But then also showing that those lead to all sorts of distortions in memory. The discovery that the act of remembering can change the memory,
it can strengthen it, but it can also distort it
if you get misinformation at the time. And it can also strengthen
or weaken other memories that you didn't even recall. So just this whole idea of
memory as an ecosystem, I think, was a big discovery. I could go on. This idea of like breaking
up our continuous experience into these discreet events, I
think was a major discovery. - So the discreetness of
our encoding of events? - Maybe, yeah. I mean, you know, and again,
there's controversial ideas about this, right? But it's like, yeah, this idea that... And this gets back to just
this common experience of you walk into the
kitchen and you're like, "Why am I here?" And you just end up grabbing
some food from the fridge and then you go back and you're
like, "Oh, wait a minute, I left my watch in the kitchen. That's what I was looking for." And so what happens is, is that you have a little internal model of where you are, what you're thinking about, and when you cross from
one room to another those models get updated. And so now when you're in the
kitchen you have to go back and mentally time travel
back to this earlier point to remember what it was
that you went there for. And so these event boundaries... Turns out, like in our research, and, again, I don't wanna make
it sound like we've figured out everything, but in our
research, one of the things that we found is, is that
basically as people get older, the activity in the hippocampus
at these event boundaries tends to go down. But independent of age,
if I give you outside of the scanner, you're
done with the scanner, I just scan you while
you're watching a movie, you just watch it, you
come out, I give you a test of memory for stories, what happens is you find
this incredible correlation between the activity in the hippocampus at these singular points in time, these event boundaries, and your ability to just remember a story outside of the scanner later on. So it's marking this
ability to encode memories, just these little snippets
of neural activity. So I think that's a big one. There's all sorts of work in animal models that I can get into, you know, sleep. I think there's so much interesting stuff that's being discovered
in sleep right now. Being able to just record from
large populations of cells and then be able to relate that. You know, one, I think the coolest thing, gets back to this QR code thing, because like what we can do
now is like I can take FMRI data while you're watching a movie... Or let's do better than that. Let me get FMRI data
while you use a joystick to move around in virtual reality. You're in the metaverse, whatever, right? But it's kind of a crappy metaverse 'cause there's always so
much metaverse you can do in an MRI scanner. So you're doing this
crappy metaverse thing. So now I can take a rat,
record from his hippocampus and prefrontal cortex,
and all these areas, with these really new electrodes and get massive amounts of data and have it move around on a
track ball in virtual reality in the same metaverse that I did and record that rats activity. I can get a person with epilepsy, who we have electrodes
in their brain anyway to try to figure out where
the seizures are coming from, and if it's a healthy part of the brain record from that person, right? And I can get a computational model. And one of the brand new
members in my lab, Tyler Bonnen, is just doing some great stuff. He relates computer vision models and looks at the weaknesses
of computer vision models and relates it to what
the brain does well. - [Lex] Mm, nice. - And so you can actually
take a ground truth, you know, code for the
metaverse, basically, And you can feed in
the visual information, let's say the sensory information, or whatever, that's coming
in to a computational model that's designed to take
real world inputs, right? And you could basically
tie them all together by virtue of the state
spaces that you're measuring in neural activity in
these different formats, and these different species, And in the computational
model, which is just... I just find that mind blowing. You could do different kinds
of analyses on language and basically come up with just like the, basically it's the guts of LLMs, right? You have, you could do
analyses on language and you could do analyses on,
you know, sentiment analysis of emotions and so forth. Put all the stuff together. I mean, it's almost too much. But if you do it right, and you
do it in a theory driven way as opposed to just throwing
all the data at the wall and see what sticks, I mean that to me is just
exceptionally powerful. - So you can take FMRI
data in across species and across different types of humans, or conditions of humans and,
what, find construct models that help you find the commonalities, or like the core thing that
makes somebody navigate through the metaverse, for example? - Yeah, yeah. I mean more or less. I mean there's a lot of
details but yes, I think... And not just FMRI, but you can relate it to, like I said, recordings from large
populations of neurons that could be taken in a human or even in a non-human animal, that is, you know, where you think it's an anatomical homolog. So that's just mind blowing to me. - What's the similarities
in humans and mice? (Charan laughing) - I love it.
- That's what The Smashing Pumpkins, "We're
all just rats in a cage." Is that Smashing Pumpkins? - "Despite all of your rage." - Is that Smashing Pumpkins? I think, or all- - Despite all of your rage at GIFs, you're still just rat in a cage. - Oh, yeah. All right, good callback. Anyway.
- It is a good callback. See these memory retrieval
exercise I'm doing are actually helping you
build a lasting memory of this conversation. - And it's strengthening the
pic, the visual thing I have of you with James Brown on stage. It's just becoming stronger
and stronger by the second. Anyway-
- The hot tub. (both laughing) - But animal studies work here as well? - Yeah, yeah. So, okay, so let's go to the... So I think recent, I've got,
you know, great colleagues who I talk to who study memory in mice, you know, and there's some... One of the valuable things in those models is you can study neural circuits in an enormously targeted way because you could do these
genetic studies, for instance, where you can manipulate
like particular groups of neurons and it's just
getting more and more targeted, to the point where you
can actually turn on a particular kind of
memory just by activating a particular set of
neurons that was active during an experience. Right? So there's a lot of conservation of some of these neural
circuits across, you know, evolution in mammals for instance. And then, you know, some
people would even say that there's genetic
mechanisms for learning that are conservative even
going back far, far before. But let's go back to the mice
and humans question, right? There's a lot of differences. So for one thing, the sensory
information is very different. Mice and rats explore the world largely through smelling, olfaction, but they also have vision
that's kind of designed to kind of catch death from above. So it's like a very big view of the world. And we move our eyes around in a way that focuses on particular spots in space where you get very high resolution from a very limited set of spots in space. So that makes us very
different in that way. We also have all these other
structures as social animals that allow us to respond differently. There's language, there's
like, you know, so you name it, there's obviously gobs of differences. Humans aren't just giant rats, there's much more complexity to us. Timescales are very important. So primate brains and human
brains are especially good at integrating and and
holding on to information across longer and longer periods of time. Right? And and also, you know,
finally it's like our history of training data, so to
speak, is very, very different than, you know, I mean a
human's world is very different than a wild mouse's world. And a lab mouse's world is
extraordinarily impoverished relative to an adult human. You know? - But still, what can you
understand by studying mice? I mean just basic, almost
behavioral stuff about memory? - Well yes, but that's
very important, right? So you can understand for
instance, how do neurons talk to each other? That's a really big, big question. Neural computation in and of itself... You'd think it's the most
simple question, right? Not at all. I mean it's a big, big question and understanding how two
parts of the brain interact, meaning that it's not
just one area speaking, it's not like, you know,
it's not like Twitter where one area of the brain's shouting and then another area of the
brain's just stuck listening to this crap. It's like they're actually interacting on the millisecond scale, right? How does that happen,
and how do you regulate those interactions, these
dynamic, you know, interactions? We're still figuring that out. But that's gonna be coming
largely from model systems that are easier to understand. You can do manipulations
like drug manipulations to manipulate circuits and, you know, use viruses, and so forth, and lasers to turn on circuits that you just can't do in humans. So I think there's a lot that
can be learned from mice, there's a lot that can be
learned from non-human primates, and then there's a lot that
you need to learn from humans. And I think, unfortunately,
some of the people in the National Institutes
of Health think you can learn everything from the mouse. Like why study memory in
humans when I could study learning in a mouse? And just like, oh my god,
I'm gonna get my funding from somewhere else. So... - Well let me ask you some
random, fascinating questions. - [Charan] Yeah, sure. - How does deja vu work? - So deja vu is, it's actually
one of these things I think that some of the surveys
suggest that like 75% of people report having
a deja vu experience one time or another. I don't know where that came from but I've polled people in my class and most of them say
they've experienced deja vu. It's this kind of sense that
I've experienced this moment sometime before, I've been here before. And actually there's all
sorts of variants of this. The French have all sorts of names for various versions of this. (speaking in French) I dunno, whatever, it's like
all these different vus. - [Lex] Yeah. - But deja vu is the sense that it can be like an almost disturbing,
intense sense of familiarity. So there was a researcher
named Wilder Penfield. Actually, this goes back even earlier, to some of the earliest... Like Hughlings Jackson was
this neurologist who did a lot of the early
characterizations of epilepsy. And one of the things he
notices in epilepsy patients, some group of them, right
before they would get a seizure, they would have this
intense sense of deja vu. So it's this artificial
sense of familiarity, it's a sense of having a
memory that's not there. Right? And so what was happening was
there was electrical activity in certain parts of these brains
and so this guy, Penfield, later on, when he was trying to look for how do we map out
the brain to figure out which parts we wanna remove
and which parts don't we, he would stimulate parts of
the temporal lobes of the brain and find you could elicit
the sense of deja vu. Sometimes you'd actually get a memory, that a person would re-experience, just from electrically
stimulating some parts. Sometimes though they would
just have this intense feeling of being somewhere before. And so one theory which I really like is, is that in higher
order areas of the brain that are integrating for
many, many different, you know, sources of input what happens is, is that they're tuning themselves up every time you process
a similar input, right? And so that allows you to just get this kind of affluent sense
that I'm very familiar, you're very familiar
with this place, right? And so just being here, you're not going to be moving your eyes all over the place 'cause you kind of have an
idea of where everything is. And that fluency gives you
a sense of like, I'm here. Now I wake up in my hotel room and I have this very unfamiliar
sense of where I am, right? But, you know, there's a
great set of studies done by Anne Cleary at Colorado State where she created these
virtual reality environments. And we'll go back to the metaverse. Imagine you go through
a virtual museum, right? And then she would put
people in virtual reality and have them go through a virtual arcade. But the map of the two
places was exactly the same, she just put different skins on them so one looks different than the other, but they've got same landmarks and same places, same
objects and everything. But carpeting, colors, theme,
everything's different. People will often not
have any conscious idea that the two are the same, but they could report this
very intense sense of deja vu. So it's like a partial
match that's soliciting this kind of a sense of familiarity. And that's why, you know, in
patients who have epilepsy that affects memory, you
get this artificial sense of familiarity that happens. And so we think that... And, again, this is just
one theory amongst many, but we think we get a
little bit of that feeling, it's not enough to
necessarily give you deja vu, even for very mundane things, right? So it's like if I tell
you the word rutabaga, your brain's gonna work a
little bit harder to catch it than if I give you word like apple. Right? And that's 'cause you hear apple a lot, so your brain's very tuned
up to process it efficiently. But rutabaga takes a little
bit longer, and more intense. And you can actually see a
difference in brain activity in areas in the temporal
lobe when you hear a word just based on how frequent it
is in the English language. So- - [Lex] That's fascinating. - We think it's tied to this basic... It's a basically a
byproduct of our mechanism of just learning, doing this
error driven learning as we go through life to become better and better and better to process things
more and more efficiently. - So I guess deja vu was
just thinking extra elevated, the stuff coming together, firing for this artificial memory
as if it's the real memory. I mean, why does it feel so intense? - Well, it doesn't happen all the time, but I think what may be
happening is it's such a... It's a partial match to
something that we have and it's not enough to trigger
that sense of, you know, that ability to pull
together all the pieces but it's a close enough match
to give you that intense sense of familiarity without the recollection of exactly what happened when. - But it's also like a
spatial temporal familiarity. So like it's also in time. Like there's a weird blending
of time that happens. And we'll probably talk about time, 'cause I think that's a
really interesting idea. - Yeah.
- How time relates to memory. But you also kind of... Artificial memory brings to
mind this idea of false memories that comes in all kinds of contexts. But how do false memories form? - Well I like to say there's
no such thing as true or false memories, right? It's like Johnny Rotten
from the Sex Pistols, he had a saying that's like, "I don't believe in false memories anymore than I believe in false songs." Right? It's like... And so the basic idea is is
that we have these memories that reflect bits and
pieces of what happened as well as our inferences
and theories, right? So I'm a scientist and I collect data, but I use theories to
make sense of that data. And so a memory is kind of
a mix of all these things. So where memories can go off the deep end and become what we would call conventionally as false memories are sometimes little distortions where we filled in the blanks,
the gaps in our memory, based on things that we know but don't actually
correspond to what happened. Right? So if I were to tell you
that I'm like, you know a story about this
person who's like worried that they have cancer, or something like that, and
then, you know, they see a doctor and the doctor says, "Well, things are very much
like you would've expected." Or like, you know, what you
were afraid of or something. When people remember that
they'll often remember, well the doctor told the
patient that he had cancer, even if that wasn't in the story, because they're infusing
meaning into that story. Right? So that's a minor distortion. But what happens is, is
that sometimes things can really get outta hand
where people have trouble telling the difference between
things that they've imagined versus things that happened. But also, as I told you, the act of remembering
can change the memory. And so what happens then is
you can actually be exposed to some misinformation. And so Elizabeth Loftus was
a real pioneer in this work, and there's lots of other
work that's been done since. But basically it's like
if you remember some event and then I tell you
something about the event later on when you remember
the event you might remember some original information from the event as well as some information
about what I told you. And sometimes if you're not
able to tell the difference, that information that
I told you gets mixed into the story that you had originally. So now I give you some
more misinformation, or you're exposed to some more
information somewhere else, and eventually your memory
becomes totally detached from what happened. And so sometimes you can
have cases where people, this is very rare, but
you can do it in lab too, where like a, you know,
significant, not everybody but, you know, a chunk of
people will fall for this, where you can give people
misinformation about an event that never took place and as
they keep trying to remember that event more and more and
what happens is they start to imagine, they start to pull up things from other experiences they've had and eventually they can
stitch together a vivid memory of something that never happened. Because they're not remembering
an event that happened, they're remembering the
act of trying to remember what happened and basically
putting it together into the wrong story. - So it's fascinating, 'cause
this could probably happen at a collective level. Like this is probably what
successful propaganda machines aim to do, this creating false memory across thousands if not millions of minds. - Yeah, absolutely. I mean this is exactly what they do. And so all these kind of
foibles of human memory get magnified when you start
to have social interactions. So there's a whole literature on something called social contagion, which is basically when
misinformation spreads like a virus. Like you remember the
same thing that I did, but I give you a little
bit of wrong information, then that becomes part of
your story of what happened. Because once you and I share
a memory, like I tell you about something I've
experienced and you tell me about your experience at the same event, it's no longer your memory or
my memory, it's our memory. And so now the misinformation spreads. And the more you trust someone, or the more powerful that person is, the more of a voice they have
in shaping that narrative. Right? And there's all sorts of interesting ways in which misinformation can happen. There's a great example
of when John McCain and George Bush Jr. were in a primary, and there were these polls where they would do these like... I guess they were like not
robocalls, but real calls where they would poll voters but they actually inserted
some misinformation about McCain's beliefs
on taxation I think, and maybe it was something
about illegitimate children, I don't really remember, but they included
misinformation in the question that they asked. Like, you know, "How do
you feel about the fact that he wants to do this?" Or something. And so people would end
up becoming convinced he had these, you know, policy things, or these personal things,
that were not true, just based on the polls
that were being used. So it was a case where,
interestingly enough, the people who were using misinformation were actually ahead of the
curve relative to the scientists who were trying to study
these effects in memory. - Yeah, it's... It's really interesting. So it's not just about truth
and falsehood as like us as intelligent reasoning machines, but it's the formation of
memories where they become like visceral, you can rewrite history. If you just look
throughout the 20th century some of the dictatorships
with Nazi Germany, with the Soviet Union,
effective propaganda machines can rewrite our conceptions of history, how we remember our own
culture, our upbringing, all this kind of stuff. And you could do quite a
lot of damage in this way. And then there's probably some kind of social contagion happening there. Like certain ideas that may be initiated by the propaganda machine can
spread faster than others. You could see that in modern day, certain conspiracy theories. There's just something about them that they are like really
effective at spreading. There's something sexy
about them to people, to where something about
the human mind eats it up and then uses that to construct memories as if they almost were there to witness whatever the content of
the conspiracy theory is. It's fascinating 'cause once
you feel like you remember a thing, I feel like there's a certainty, there's a... It emboldens you to like say stuff. Like you really like... It's not just you believe
an ideas true or not, you're like, it's at
the core of your being that you feel like you were
there to watch the thing happen. - Yeah, I mean there's so
much in what you're saying. I mean, one of the things
is, is that people's sense of collective identity is very
much tied to shared memories. If we have a shared narrative of the past, or even better, if we have a shared past we will feel more socially
connected with each other, and I will feel part of this group. They're part of my tribe if I remember the same
things in the same way. And you brought up this
weaponization of history and, you know, it really
speaks to, I think, one of the parts of memory, which is that if you have a belief you will find, and you
have a goal in mind, you will find stuff in
memory that aligns with it and you won't see the
parts in memory that don't. So a lot of the stories we put together are based on our perspectives. Right? And so let's just zoom out for the moment from like misinformation to take something even more fascinating, but not as like, you know, scary. You know, I was reading Thanh Viet Nguyen, but he wrote a book about
the collective memory of the Vietnam War. He is a Vietnamese
immigrant who was flown out after the war was over. And so he went back to his family to get their stories about the war and they called it the American
War, not the Vietnam War. Right? And that just kind of blew my mind, having grown up in the US,
and having always heard about it as the Vietnam War. But of course they call
it the American War, 'cause that's what happened. America came in, right? And that's based on their perspective, which is a very valid perspective. And so that just gives you this idea of the way we put
together these narratives based on our perspectives. And I think the opportunities
that we can have in memory is if we bring groups together
from different perspectives and we allow them to talk to each other and we allow ourselves to listen. I mean, right now you'll
hear a lot of just jammering, you know, people going blah,
blah blah about free speech, but they just wanna listen to themselves. Right? I mean it's like, let's
face it, the old days before people were supposedly woke they were trying to ban 2
Live Crew, or, you know. Just think about, Lenny Bruce
got canceled for cursing. Jesus Christ.
- Yeah. - [Charan] You know, it's like- - Yeah.
- This is nothing new. - Yeah.
- People don't like to hear things that disagree with them. But if you're in a... I mean you can see two
situations in groups with memory. One situation is you have like
people who are very dominant, who just take over the
conversation, and they... Basically what happens
is the group remembers less from the experience and they remember more of what
the dominant narrator says. Right? Now, if you have a
diverse group of people, and I don't mean diverse in
necessarily the human resources sense of the word, I
mean diverse in any way you want to take it, right? But diverse in every way, hopefully. And you give everyone a chance to speak, and everyone's being appreciated for their unique contribution, you get more accurate memories and you get more information from it. Right? Even two people who come from
very similar backgrounds, if you can appreciate
the unique contributions that each one has, you can do a better job of generating information from memory. And that's a way to inoculate
ourselves, I believe, from misinformation in the modern world. But, like everything else, it requires a certain
tolerance for discomfort. And I think when we don't have much time, and I think when we're stressed out and when we are just tired, it's very hard to tolerate discomfort. - And I mean, social media
has a lot of opportunity for this because it
enables this distributed one-on-one interaction
that you're talking about where everybody has a voice, but still our natural inclination... You see this on social media,
there's a natural clustering of people and opinions and
you just kind of, you know, form these kind of bubbles. I think that's... To me personally, I think
that's a technology problem that could be solved. If there's a little bit of interaction, kind, respectful,
compassionate interaction with people that have a
very different memory, that respectful interaction
will start to intermix the memories and ways of thinking to where you're slowly
moving towards truth. But that's a technology problem because naturally, left
to our own devices, we wanna cluster up in a tribe. - Yeah, and that's the human problem. - Yeah.
- You know. I think a lot of the problems that come up with technology aren't
the technology itself as much as the fact that
people adapt to the technology in maladaptive ways. I mean, one of my fears about
AI is not what AI will do, but what people will do. I mean, take text messaging, right? It's like it's a pain in
the ass to text people, at least for me. And so what happens is the communication becomes very spartan and
devoid of meaning, right? It's just very telegraphic. And that's people adapting
to the medium, right? I mean look at you, you've
got this keyboard, right? That's like got these
like dome shaped things, and you've adapted to that
to communicate, right? That's not the technology adapting to you, that's you adapting to the technology. And I think with, you know,
one of the things I learned when Google started to introduce
auto complete in emails, I started to use it and
about a third of the time I was like, "This isn't what I wanna say." A third of the time I'd be like, "This is exactly what I wanted to say." And a third of the time I was saying, "Well this is good enough,
I'll just go with it." Right? And so what happens is it's
not that the technology necessarily is doing anything so bad as much as it's just going
to constrain my language because I'm just doing
what's being suggested to me. And so this is why I say, you
know, kinda like my mantra for some of what I've learned
about everything in memory is to diversify your
training data basically. Because otherwise you're going to be... So like humans have this
capability to be so much more creative than anything
generative AI will put together. At least right now, who
knows where this goes. But it can also go the opposite direction where people could become
much, much less creative if they just become more
and more like resistant to discomfort, you know,
and resistant to exposing themselves to novelty, to
cognitive dissonance and so forth. - I think there is a dance
between natural human adaptation of technology and the people
that design the engineering of that technology. So I think there's a lot
of opportunity to create, like this keyboard,
things on net are positive for human behavior. So we adapt, and all this kind of stuff, but when you look at the long
arc of history across years and decades, has humanity
been flourishing? Are humans creating more awesome stuff? Are humans happier? All that kind of stuff. And so there, I think
technology on net has been, and I think, maybe hope,
will always be on net a positive thing. - Do you think people are happier now than they were 50 years
ago, or 100 years ago? - Yes. Yes. - I don't know about that. - I think humans in
general like to reminisce about the past, like
that times were better. - [Charan] That's true. - And complain about the weather today, or complain about whatever today, 'cause we, there's this
kind of complainy engine that's just, there's so
much pleasure in saying, you know, "Life sucks." For some reason. - That's why I love punk rock. - Exactly. I mean there's something in
humans that loves complaining, even about trivial things. But complaining about change,
complaining about everything. But ultimately I think,
on net, on every measure, things are getting better,
life is getting better. - Oh, life is getting better, but I don't know that necessarily that tracks people's happiness, right? I mean, I would argue
that maybe, who knows, I don't know this, but
I wouldn't be surprised if people in hunter gatherer
societies are happier. I mean, I wouldn't be
surprised if they're happier than people who have
access to modern medicine, and email, and cell phones. - Well I don't think there's
a question whether you take hunter gatherer folks and
put them into modern day and give 'em enough time to adapt, they would be much happier. The question is, in terms
of every single problem they've had is now solved. There's now food, there's
guarantee of survival, and shelter, and all this kind of stuff. - Oh.
- So what you're asking is a deeper sort of biological question. Do we want to be a Werner Herzog, that movie, "Happy People:
Life in the Taiga?" Do we want to be busy 100% of
our time hunting, gathering, surviving, worried about the next day? Maybe that constant
struggle ultimately creates a more fulfilling life. I don't know. But I do know this
modern society allows us to, when we're sick, to find
medicine, to find cures, when we're hungry, to get food, much more than we did even 100 years ago. And there's many more activities
that you could perform, all creative, all these kinds of stuff, that enables the flourishing of humans at the individual level. Whether that leads to happiness, I mean, that's a very deep
philosophical question. Maybe struggle, deep struggle,
is necessary for happiness. - Or maybe cultural connection. You know, maybe it's about like
functioning in social groups that are meaningful, and like having time. But I do think this is,
there's an interesting memory related thing,
which is that if you look at like things like reinforcement learning for instance, you're not
learning necessarily every time you get a reward, if it's the same reward, you're not learning that much. You mainly learn if it
deviates from your expectation of what you're supposed to get, right? So it's like you get a
paycheck every, you know, month from MIT, or whatever, right? And it's like you're kind
of, you probably don't even kind of get excited about it
when you get the paycheck. But if they cut your salary,
you're gonna be pissed. And if they increase your salary, you go, "Oh, good, I got a bonus." You know? And that adaptation and that ability that basically you learn
to expect these things, I think, is a major source
of, I guess it's a major way in which we're kind of more,
in my opinion, wired to strive and not be happy to be
in a state of wanting. And, you know, so people
talk about dopamine for instance, being
this pleasure chemical. And it's like there's a
lot of compelling research to suggest it's not about pleasure at all, it's about the discomfort
that energizes you to get things, to seek a reward, right? And so you could give an
animal that's been deprived of dopamine a reward and,
"Oh, yeah, I enjoy it. It's pretty good." But they're not gonna
do anything to get it. You know? And just one of the weird
things in our research is, is we, I got into
curiosity from a postdoc in my lab, Matthias Gruber,
and one of the things that we found is when we
gave people a question, like a trivia question, that
they wanted the answer to. That question, the more curious people were about the answer, the more activity in these dopamine related
circuits in the brain we would see. And, again, that was not
driven by the answer per se, but by the question. So it was not about
getting the information, it was about the drive
to seek the information. But it depends on how you take that. If you get this uncomfortable
gap between what you know and what you want to
know, you could either use that to motivate you and energize you, or you could use it to say, "I
don't wanna hear about this, this disagrees with my beliefs, I'm gonna go back to my echo chamber." You know? - Mm-hmm, yeah. I like what you said
that maybe we're designed to be in a kind of
constant state of wanting, which by the way is a
pretty good either band name or rock song name, state of wanting. - That's like a hardcore band name. - Hardcore band.
- Yeah, yeah, yeah. - [Lex] Yeah, it's pretty good. - But I also like the hedonic treadmill. - Hedonic treadmill's pretty good. - Yeah, yeah, we could use that
for like our techno project, I think. - You mean the one we're starting? - Yeah, exactly.
- Okay, great. We're going on tour soon. (Charan laughing) This is our announcement. - We could build a false
memory of a show in fact, if we want. Let's just put it all together so... We don't even have to do all
the work to play the show, we can just create a memory of it. It might as well happen, 'cause the remembering
itself is in charge anyway. - So let me ask you about, we
talked about false memories, but, you know, in the legal
system, false confessions. I remember reading "1984," where, sorry for the dark turn
of our conversation, but through torture
you can make people say anything and essentially
remember anything. I wonder to which degree
there's like truth to that. If you look at the torture that
happened in the Soviet Union for confessions, all that kind of stuff. How much can you really
get people to really, you know, to force
false memories, I guess? - Yeah, I mean I think
there's a lot of history of this actually in the
criminal justice system. You might have heard the
term the third degree. If you actually look it up, historically, it was a very
intense set of beatings and, you know, starvation
and physical demands that they would place on
people to get them to talk. And, you know, there was
certainly a lot of work that's been done by the CIA in terms of enhanced interrogation techniques. And, from what I understand,
the research actually shows that they just produce
what people want to hear, not necessarily the information
that is being looked for. And the reason is, is that... I mean, there's different reasons. I mean, one is people just get tired of being tortured and just say whatever. But another part of it
is, is that you create a very interesting set of conditions where there's an authority
figure telling you something that, "You did
this, we know you did this, we have witnesses saying you did this." So now you start to question yourself. Then they put you under stress. Maybe they're not feeding you, maybe they're kinda
like making you be cold or, you know, exposing you to like music that you can't stand, or something. Whatever it is, right? It's like they're creating
this physical stress. And so stress starts to
act on, you know, starts to downregulate the prefrontal cortex. You're not necessarily
as good at monitoring the accuracy of stuff. Then they start to get
nice to you and they say, "Imagine..." You know, "Okay, I know
you don't remember this, but maybe we can walk you through how it could have happened." And they feed you the information. And so you're in this
weakened mental state and you're being encouraged
to imagine things by people who give you
a plausible scenario. And at some point certain
people can be very coaxed into creating a memory for
something that never happened. And there's actually some
pretty convincing cases out there where you don't
know exactly the truth. There's a sheriff, for
instance, who came to believe that he had a false memory. I mean that he had a memory
of doing sexual abuse based on, you know,
essentially I think it was... You know, I'm not gonna tell the story because I don't remember it well enough to necessarily accurately give it to you, but people could look this stuff up. There are definitely
stories out there like this where people confess to crimes
that they just didn't do, and objective evidence came out later on. But there's a basic recipe for it, which is you feed people the information that you want them to
remember, you stress them out, you have an authority figure kind of like pushing
this information on them, or you motivate them to
produce the information you're looking for. And that pretty much over
time gives you what you want. - It's really tragic
that centralized power can use these kinds of
tools to destroy lives. Sad. Since there's a theme about music throughout this conversation, one of the best topics
for songs is heartbreak, love in general, but heartbreak. Why and how do we remember
and forget heartbreak? Asking for a friend. - Oh, God, that's so hard to... Asking for a friend, I love that. Oh, it's such a hard one. Well, so I mean part of
this is we tend to go back to particular times that are the more
emotionally intense periods. And so that's a part of it. And, again, memory's designed to kind of capture these things that are biologically significant, and attachment is a, you know, big part of biological significance for humans. Right? Human relationships are super important. And sometimes that heartbreak
comes with massive changes in your beliefs about somebody, say if they cheated on you,
or something like that, or regrets, and you kind
of ruminate about things that you've done wrong. There's really so many reasons though. But, you know, I mean, I've had this. My first pet I had as, you know, was, we got it for a
wedding present, was a cat and got it after like... But it died of FIP when
it was four years old. And, you know, I just
would see her everywhere around the house, you know. We got another cat, then we got a dog, dog eventually died of cancer and the cat just died recently. And, you know, so we got a new dog because I kept seeing the dog around and I was just so heartbroken
about this, and... But I still remember the pets that died. It just comes back to you. I mean, it's part of this... I think there's also
something about attachment that's just so crucial that drives, again, these things that we want to remember and that gives us that longing sometimes. Sometimes it's also not
just about the heartbreak, but about the positive
aspects of it, right? 'Cause the loss comes
from not only the fact that the relationship is over, but you had all of these good things before that you can now
see in a new light, right? And so part of, one of the things that I found from my clinical background that really I think gave
me a different perspective on memory is so much
of the therapy process was guided towards reframing
and getting people to look at the past in a different way. Not by imposing, changing
people's memories, or not by imposing an interpretation, but just offering a different perspective and maybe one that's kind of
more optimized towards learning and, you know, and appreciation maybe, or gratitude, whatever it is, right? That gives you a way of taking... I think you said it in
the beginning, right? Where you can have this kind
of like dark experiences and you can use it as training data to, you know, grow in new ways. But it's hard. - This... I often go back to this
moment, this show "Louis," with Louis C.K., where he's
all heartbroken about a breakup with a woman he loves and
an older gentleman tells him that that's actually the
best part, that heartbreak, because you get to intensely experience how valuable this love was. He says the worst part is forgetting it. It's actually when you
get over the heartbreak, that's the worst part. So I sometimes think about
that because, you know, having the love and losing it, like the losing it is
when you sometimes feel it the deepest, which is a
interesting way to celebrate the past and relive it. It sucks that you don't have a thing, but when you don't have a
thing it's a good moment to viscerally experience the memories of something that you
now appreciate even more. - So you don't believe that
an owner of a lonely heart is much better than an
owner of a broken heart? You think an owner of a broken heart is better than the
owner of a lonely heart? - Yes, for sure. I think so. I think so. But I'm gonna have to, day by day... I don't know, I'm gonna have to listen to some more Bruce Springsteen
to figure that one out. (Charan laughing) - Well, you know, it's funny because it's like after I turned 50 I think of death all the time. Like I just think that, you
know, I'm in, like, I probably, I have fewer, probably
have fewer years ahead of me than I have behind me, right? So I think about, I think about one thing, which is what are the memories
that I wanna carry with me for the next period of time? And also about like, just
the fact that everything around me could be, you
know, I know more people who are, you know, dying
for various reasons. And so... I mean, not lots, I'm not that old, right? It's like... But, you know, it's
something I think about a lot and I'm reminded of like how I talk to somebody who's like,
you know, who's a Buddhist, and I was like, you know,
the whole idea of Buddhism is renouncing attachment. In some way the idea of
Buddhism is like staying out of the world of memory and
staying in the moment, right? And they talked about, you
know, it's like how do you, how do you renounce
attachments to the people that you love, right? And they're just saying, "Well, I appreciate that I
have this moment with them and knowing that they will
die makes me appreciate this moment that much more." I mean, you said something similar, right? In your daily routine that you
think about things this way. Right? - Yeah, I meditate on mortality every day. But, I don't know, I... At the same time, that
really makes you appreciate the moment and live in the moment, and I also appreciate the
full, deep rollercoaster of suffering involved in life. The little and the big too. So I don't know. The Buddhist kinda removing
yourself from the world, or the stoic removing
yourself from the world, the world of emotion,
I'm torn about that one. I'm not sure. - Well, you know, this is
where Hinduism and Buddhism, or at least some strains of
Hinduism and Buddhism, differ. In Hinduism, like if you
read the Bhagavad Gita, the philosophy is not one
of renouncing the world, because the idea is, is
that not doing something is no different than
doing something, right? So what they argue... And, again, you could
interpret it in different ways, positive and negative, but the argument is, is that you don't
want to renounce action, but you want to renounce
the fruits of the action. You don't do it because of the outcome, you do it because of the process, because the process is part
of the balance of the world that you're trying to preserve, right? And of course you could
take that different ways, but I really think about
that from time to time in terms of like, you know,
letting go of this idea of does this book sell, or
trying to, you know, like impress you and get you to laugh
at my jokes or whatever, and just be more like I'm
sharing this information with you and, you know,
getting to know you, or whatever it is. But it's hard, right? It's like, 'cause we're so
driven by the reinforcer, the outcome. - You're just part of the
process of telling the joke, and if I laugh or not, that's
up to the universe to decide. - Yep, it's my dharma. - How does studying memory
affect your understanding of the nature of time? So like we've been talking
about us living in the present and making decisions about the future, standing on the foundation
of these memories and narratives about the
memories that we've constructed. So it feels like it does
weird things to time. - Yeah, and the reason
is, is that in some sense, I think, especially
the farther we go back, I mean there's all sorts of
interesting things that happen. So your sense of like if
I ask you how different does one hour ago feel from two hours ago? You'd probably say pretty different. But if I ask you, okay,
go back one year ago versus one year and one hour ago, it's the same difference in time. It won't feel very different, right? So there's this kind of
compression that happens as you look back farther in time. So that it is kinda like
why when you're older the difference between
somebody who's like 50 and, you know, 45 doesn't
seem as big as the difference between like 10 and five
or something, right? When you're 10 years old, everything seems like it's a long period of time. Here's the point is that, you know, so one of the interesting things that
I found when I was working on the book actually,
was during the pandemic, I just decided to ask people in my class, when we were doing the remote instruction. So one of the things I did
was I would poll people. And so I just asked people, "Do you feel like the
days are moving by slower or faster, or about the same?" Almost everyone in the class said that the days were moving by slower. So then I would say, "Okay, so do you feel like the weeks are passing by
slower, faster or the same?" And the majority of them said that the weeks were passing by faster. So, according to the laws of physics, I don't think that makes any sense, right? - [Lex] Yeah. - But according to memory it did, because what happened was
people were doing the same thing over and over in the same context. And without that change
in context their feeling was that they were in one
long monotonous event. And so... But then at the end of
the week you look back at that week and you say,
"Well what happened?" I have no memories of what happened. So that week just went by
without even my noticing it. But that week went by during
the same amount of time as an eventful week where
you might've been going out, hanging out with friends, on
vacation, or whatever, right? It's just that nothing happened because you're doing the
same thing over and over. So I feel like memory really
shapes our sense of time, but it does so in part because context is so
important for memory. - Well that compression you mentioned, it's an interesting process. 'Cause when I think about
when I was like 12 or 15, I just fundamentally feel
like the same person. It's interesting what
that compression does. It makes me feel like it's
all, we're all connected, not just amongst humans and spatially, but in terms, back in time, there's a kinda eternal nature, like the timelessness, I guess, to life. That could be also a
genetic thing just for me, I don't know if everyone
agrees to this view of time. But to me it all feels the same. - Like you don't feel the
passage of time, or... - No, I feel the passage
of time the same way that your students did from day to day. There's certain markers that let you know that time has passed, you
celebrate birthdays, and so on. But the core of who I am
and who others I know are, or events it like that
compression of my understanding of the world removes time. 'Cause time is not useful
for the compression. So like the details of
that time, at least for me, is not useful to understanding
the core of the thing. So... - Maybe what it is is is
that you really like to see connections between things. This is like really what motivates me in science actually too. But it's like when you
start recalling the past to, you know, and seeing the
connections between the past and present, now you have this kind of web of interconnected memories, right? And so I can imagine in that sense there is this kind of, the
present is with you, right? But what's interesting
about what you said too that struck me is that
your 16-year-old self was probably very complex, you know. And I, by the way, I'm the same way, but it's like it really is the source of a lot of darkness for me. So... But when like you can look
back at like, let's say you hear a song that you used to play like before you would
go do a sports thing, or something like that. And you might not think
of yourself as an athlete, but once you get back to that mental, you mentally time travel
to that particular thing, you open up this little
compartment of yourself that wasn't there before, right? That didn't seem accessible before. Dan Schacter's lab did
this really cool study where they would ask people to either remember doing
something altruistic or imagine doing something altruistic and that act made them more likely to want to do things for other people. So that act of mental
time travel can change who you are in the present. And we tend to think of... This goes back to that
illusion of stability. And we tend to think of memory
in this very deterministic way, that I am who I am
because I have this past. But we have a very multifaceted
past and can access different parts of it
and change in the moment based on whatever part we wanna reach for. Right? - How does nostalgia connect
into this, like this desire and pleasure associated with going back? - Yeah, so my friend Felipe
De Brigard wrote this, and it just like blew my
mind, where the word nostalgia was coined by a Swiss physician who was actually studying
traumatized soldiers, and so he described
nostalgia as a disease. And the idea was it was bringing
these people extraordinary unhappiness because they're remembering how things used to be. And I think it's very complex. So as people get older, for instance, nostalgia can be an enormous
source of happiness, right? And being nostalgic can improve people's moods in the moment. But it just depends on
what they do with it. Because what you can
sometimes see is nostalgia has the opposite effect of thinking, "Those were the good old days
and those days are over." Right? It's like America used to be
so great and now it sucks. Or, you know, my life used to
be so great when I was a kid and now it's not. Right? And you're selectively
remembering the things that... I mean, we don't realize how selective our remembering self is. And so, you know, I lived
through the seventies, it sucked, you know, it was like... Partly it sucked more for me, but I would say that even otherwise it's like there's all
sorts of problems going on. Gas lines, people were like, you know, worried about like Russia,
nuclear war, blah, blah blah. So I mean it's just this idea that people have about the
past can be very useful if it brings you happiness in the present, but if it narrows your
worldview in the present, you're not aware of those
biases that you have, you will end up, you can end
up, it can be toxic, right? Either at a personal level
or at a collective level. - Let me ask you both a practical question and an out there question. So let's start with
the more practical one. What are your thoughts about BCIs, brain-computer interfaces, and the work that's
going on with Neuralink? We talked about electrodes and different ways of measuring the brain and here Neuralink is working on basically two-way
communication with the brain. And the more out there
question will be like, where does this go? But more practically in the near term, what do you think about Neuralink? - Yeah, I mean I can't say
specifics about the company 'cause I haven't studied it that much. But I mean, I think
there's two parts of it. So one is they're developing
some really interesting technology, I think with
these like surgical robots, and things like that. BCI though has like a whole
lot of innovation going on and I'm not necessarily
seeing any scientific evidence from Neuralink, and maybe that's just 'cause I'm not looking
for it, but I'm not seeing the evidence that they're anywhere near where the scientific community is. And there's lots of startups that are doing incredibly
innovative stuff. One of my colleagues Sergey
Stavisky is just like a genius in this area and they're working on it. I think speech prosthetics
like that are incorporating, you know, decoding techniques with AI and, you know, movement perspectives. It's just like the rate of
progress is just enormous. So part of the technology
is having good enough data and understanding which data to use and what to do with it, right? And then the other part of
it then is the algorithms for decoding it and so forth. And I think part of
that has really resulted in some real breakthroughs
in neuroscience as a result. So there's lots of new
technologies like neuropixels, for instance, that allow
you to harvest activity from many, many neurons
from a single electrode. I know Neuralink has some technologies that are also along these
lines, but I haven't... Again, because they do their own stuff, the scientific community doesn't see it. Right? But I think BCI is much,
much bigger than Neuralink and there's just so much
innovation happening. I think the interesting
question which we may be getting into is, I was talking
to Sergey a while ago about, you know, so a lot of language, it's not just what we
hear and what we speak, but also our intentions
and our internal models and, you know, so are
you really gonna be able to restore language without
dealing with that part of it? And he brought up a really
interesting question, which is the ethics of reading
out people's intentions and understanding of the
world as opposed to the more, you know, the more
concrete parts of hearing and producing movements. Right? - Just so we're clear, 'cause you said a few interesting things. When we talk about language and BCIs, what we mean is getting
signal from the brain and generating the language. Say you're not able to actually speak, it's as a kind of linguistic prosthetic, or it's able to speak for you exactly what you wanted to say. And then the deeper question
is, well, saying something isn't just the letters, the
words that you're saying, it's also the intention behind it, the feeling behind,
all that kind of stuff, and is it ethical to
reveal that full shebang, the full context of what's
going on in our brain. That's really... That's really interesting. That's really interesting. I mean, our thoughts, is it ethical for anyone to
have access to our thoughts? Because right now the re
the resolution is so low that we're okay with it, even doing studies and
all this kind of stuff. But if neuroscience
has a few breakthroughs to where you can start
to map out the QR codes for different thoughts, for
different kinds of thoughts, maybe political thoughts,
you know, McCarthyism, what if I'm getting a lot
of them communist thoughts? Or however we want to
categorize or label it. That's interesting. That's really interesting. I think ultimately this
always the more transparency there is about the human
mind, the better it is. But there could be always
intermediate battles with how much control
does a centralized entity have, like a government and so on. What is the regulation,
what are the rules? What are the... What's legal and illegal? You know, if you talk about the police whose job is to track
down criminals, and so on, and you look at all the history, how the police could abuse its power to control the citizenry,
all that kind of stuff. So people are always
paranoid, and rightfully so. It's fascinating. It's really fascinating. You know, we talk about freedom of speech, you know, freedom of thought, which is also a very important liberty at the core of this country,
and probably humanity, starts to get awfully tricky
when you start to be able to collect those thoughts. But what I wanted to actually
ask you is do you think, for fun and for practical
purposes, you'll be able to, we would be able to modify memories? So how difficult is it to... How far away we are from
understanding the different parts of the brain, everything
we've been talking about, in order to figure out how
can we adjust this memory at the crude level from
unpleasant to pleasant? You talked about we can remember the mall and the people, like
location of the people. Can we keep the people
and change the place? Like this kind of stuff. How difficult is that? - Well, I mean in some sense we know we can do it just behaviorally, right? - [Lex] Behaviorally, yes. - I can just like tell you, give, you know, under
certain conditions anyway, I can give you the misinformation and then you can change the people and the places and so forth, right? On the crude level, there's a lot of work that's being done on a phenomenon
called reconsolidation, which is the idea that essentially
when I recall a memory, what happens is, is that the
connections between the neurons and that cell assembly
that give you the memory are going to be like more modifiable. And so some people have used techniques to try to like, for instance,
with fear memories to reduce that physical visceral
component of the memory when it's being activated. Right now I think I've, as an
outsider looking at the data, I think it's like mixed results. And part of it is, and this
speaks to the more complex issue, is that you
don't, you need somebody to actually fully recall
that traumatic memory in the first place, in
order to actually modify it. And then what is the memory? That is the key part of the problem. So if we go back to
reading people's thoughts, what is the thought? I mean people can sometimes
look at this like behaviorists and go, "Well the memory
is like I've given you A and you produce B." But I think that's a very
bankrupt concept about memory. I think it's much more
complicated than that. And, you know, one of the
things that when we started studying naturalistic memory,
like memory from movies, that was so hard was we had to change the way we did the studies. Because if I show you a movie and I show and I watch the same movie and you recall everything that happened and I recall everything that happened, we might take a different
amount of time to do it, we might use different words, and yet to an outside observer we might have recalled the same thing. Right? So it's not about the words necessarily and it's not about how
long we spent, or whatever. There's something deeper that
is there that's this idea. But it's like, how do you
understand that thought? I encounter a lot of concrete thinking that it's like if I show
a model, like, you know, the visual information that a
person sees when they drive, I can basically reverse engineer driving. Well that's not really how it works. I once saw a talk by somebody, or I saw somebody talking
in this discussion between neuroscientists and AI people and he was saying that the
problem with self-driving cars that they had in cities
as opposed to highways was that the car was okay at,
you know, doing the things that it's supposed to, but
when there were pedestrians around it couldn't predict
the intentions of people. And so that unpredictability
of people was the problem that they were having in, you know, the self-driving car design. 'Cause it didn't have a
good enough internal model of what the people were, you know, what they were doing, what they wanted. And what do you think about that? - Well, I spent a huge amount
of time watching pedestrians, thinking about pedestrians,
thinking about what it takes to solve the problem of measuring, detecting the intention of a pedestrian, really, of a human being
in this particular context of having to cross the street. And it's fascinating. I think... I think it's a window into
how complex social systems are that involve humans because, you know, I
would just stand there and watch intersections for hours. And what you start to
figure out is every single intersection has its own personality. So like there's a history
to that intersection, like jaywalking. Certain intersections allow
jaywalking a lot more, because what happens is
we're leaders and followers. So there's a regular, let's
say, and they get off the subway and they start crossing on a red light, and they do this every single day. And then there's people that don't show up to that intersection often, and they're looking for cues of how we're supposed to behave here. And if a few people start to jaywalk and cross on a red light, they will also. They will follow. And there's just a dynamic
to that intersection. There's a spirit to it. And if you look at Boston versus New York versus a rural town versus... Even Boston, San Francisco,
or here in Austin, there's just different
personalities citywide, but there's different
personalities area wide, region wide, and there's
different personalities, different intersections. And it's just fascinating. For a car to be able to
determine that is tricky. Now what machine learning
systems are able to do well is collect a huge amount of data. So for us it's tricky because we get to like
understand the world with very limited information. - [Charan] That's right. - And make decisions grounded
in this big foundation model that we've built of
understanding how humans work. AI could literally, in
the context of driving, this is where I've often been really torn in both directions. If you just collect a huge amount of data, all of that information, and then compress it into a representation of
how humans cross streets, it's probably all there. In the same way that you
have a Noam Chomsky who says, "No, no, no, AI can't talk, can't write convincing language without understanding language." And, you know, more and more
you see large language models without quote unquote
understanding can generate very convincing language. But I think what the
process of compression, from a huge amount of data
compressing into a representation is doing is in fact understanding deeply. In order to be able to
generate one letter at a time, one word at a time, you have to understand the cruelty of Nazi Germany and the beauty of sending humans to space. And like you have to understand all of that in order to generate, like, "I'm going to the
kitchen to get an apple," and do that grammatically correctly. You have to have a world model that includes all of human behavior. - You think an LLM is
building that world model? - It has to, in order
to be good at generating one word at a time in
a convincing sentence. And in the same way I
think AI that drives a car, if it has enough data, we'll
be able to form a world model that we'll be able to predict correctly what the pedestrian does. But when we as humans
are watching pedestrians we slowly realize, "Damn,
this is really complicated." In fact, when you start to
self-reflect on driving, you realize driving is really complicated. There's like subtle cues
we take about like... Just, there's a million
things I could say, but like one of them,
determining who around you is an asshole, aggressive driver. - Yes. Yes.
- Potentially dangerous. - I was just thinking about this. Yes.
- Or like- - You can read it a mile... Once you become a great driver
you can see it a mile away, this guy's gonna pull an
asshole move in front of you. - [Lex] Yeah, exactly. - He's like way back there but
you know it's gonna happen. - And then I don't know what... 'Cause we're ignoring all the other cars. - Yeah.
- But for some reason the asshole, like a red, like
a glowing, obvious symbol is just like right there
even in the periphery vision. 'Cause we're, again, we're,
usually when we're driving just looking forward, but we're like using the periphery vision to figure stuff out and it's like a little puzzle that we're usually only
allocating a small amount of our attention to, at least
like cognitive attention to. And it's fascinating. But I think AI just has a
fundamentally different suite of sensors, in terms of
the bandwidth of data that's coming in, that allows
you to form the representation and perform inference
on the representation using the representation you form that for the case of driving, I think it could be quite effective. But one of the things
that's currently missing, even though OpenAI just recently
announced adding memory. And I did wanna ask you
like how important it is, how difficult is it to add
some of the memory mechanisms that you've seen in humans to AI systems? - I would say superficially not that hard, but then in a deeper
level, very, very hard. Because we don't understand
episodic memory, right? So one of the ideas I
talk about in the book is one of the oldest kind of dilemmas in computational neurosciences,
what Steve Grossberg called the stability plasticity dilemma, right? When do you say something is new and overwrite your preexisting knowledge versus going with what you had before and making incremental changes? And so, you know, part of the problem with going through like
massive, you know what I mean? Part of the problem of
things like if you're trying to design an LLM, or something like that, is, especially for English,
there's so many exceptions to the rules, right? And so if you wanna rapidly
learn the exceptions, you're gonna lose the rules. And if you wanna keep the rules, you have a harder time
learning the exception. And so David Marr is one
of the early pioneers in computational neuroscience, and then Jay McClelland and my colleague Randy O'Reilly, some other people like Neil
Cohen, all these people started to come up with the idea that maybe that's part of what we need in what the human brain is doing is we have this kind of a,
actually a fairly dumb system, which just says this happened
once at this point in time, which we call episodic
memory, so to speak, and then we have this knowledge that we've accumulated
from our experiences as semantic memory. So now when we want to... We encounter a situation that's surprising and violates all our
previous expectations, what happens is, is that now
we can form an episodic memory here and the next time we're
in a similar situation, boom, we can supplement our knowledge with this information
from our episodic memory and reason about what the
right thing to do is, right? So it gives us this enormous
amount of flexibility to stop on a dime and change
without having to erase everything we've already learned. And that solution is incredibly powerful because it gives you
of the ability to learn from so much less
information, really, right? And it gives you that flexibility. So one of the things I think
that makes humans great is having both episodic
and semantic memory. Now can you build something like that? You know, computational
neuroscience people would say, "Well, yeah, you just record a moment and you just get it and you're done." Right? But when do you record that moment? How much do you record? What's the information you prioritize and what's the information you don't? These are the hard questions. When do you use episodic memory? When do you just throw it away? And these are the hard
questions we're still trying to figure out in people. And then you start to think
about all these mechanisms that we have in the brain for figuring out some of these things. And it's not just one,
but it's many of them that are interacting with each other. And then you just take
not only the episodic and the semantic, but then you start to take the motivational,
survival things, right? It's just like the fight
or flight responses that we associate with particular things, or the kind of like reward motivation that we associate with
certain things, so forth. And those things are absent from AI. I frankly don't know if we want it. I don't necessarily want a
self-motivated LLM, right? It's like... And then there's the problem
of how do you even like build the motivations that should
guide a proper reinforcement learning kind of thing, for instance? So a friend of mine, Sam
Gershman, I might be missing the quote exactly, but he basically said, "You know, if I wanted to
train like a typical AI model to make me as much money as possible, first thing I might do is sell my house." So it's not even just
about having one goal, or one objective, but just
having all these competing goals and objectives, right? And then things start to
get really complicated. - Well it's all interconnected. I mean, just even the thing
you've mentioned is the moment, you know, if we record
a moment like the... It's difficult to express
concretely what a moment is, like how deeply connected
it is to the entirety of it. Maybe to record a moment you have to make a universe from scratch. Like you have to have, you
have to include everything, you have to include all
the emotions involved, all the context, all the
things that built around it, all the social connections,
all the visual experiences, all the sensory experience, all of that, all the
history that came before that moment is built on. And we somehow, we take all
of that and we compress it and keep the useful parts and then integrate it
into the whole thing, into our whole narrative. And then each individual
has their own little version of that narrative and then we collide. In a social way.
- Yeah. - [Lex] And then we
adjust it, and we evolve. - Yeah, yeah. I mean, well even if we
wanna go super simple, right? Like Tyler Bonnen, who's a
postdoc who's collaborating with me, he actually studied a lot of computer vision at Stanford. And so one of the things he was
interested in is some people who have brain damage
in areas of the brain that were thought to be
important for memory, but they also seemed to have
some perception problems with particular kinds
of object perception. And this is super controversial and some people found
this effect, some didn't. And he went back to computer vision and he said, "Let's take
the best state of the art computer vision models and let's give them the same kinds of perception tests that we were giving to these people." And then he would find the images where the computer vision
models would just struggle. And you would find that
they just didn't do well. Even if you add more
parameters, you add more layers on and on and on, it doesn't help, right? The architecture didn't matter, it was just there, the problem. And then he found those
were the exact ones where these humans with particular damage to this area called the perineal cortex, that was where they were struggling. So somehow this brain area
was being, was important for being able to do these
things that were adversarial to these computer vision models. So then he found that it only happened if people had enough time they could make those discriminations,
but without enough time, if they just get a glance, they're just like the
computer vision models. So then what he started to say was, "Well maybe let's look at people's eyes." Right? So a computer vision
model sees every pixel all at once, right? It's not, you know... And we don't, we never see
every pixel all at once. Even if I'm looking at
a screen with pixels, I'm not seeing every pixel at once. I'm grabbing little points on
the screen by moving my eyes around and getting a very
high resolution picture of what I'm focusing on and kind of a lower resolution information about everything else. But I'm not necessarily choosing, but I'm directing that exploration. And allowing people to move their eyes and integrate that information
gave them something that the computer vision
models weren't able to do. So somehow integrating
information across time and getting less information at each step gave you more out of the process. - I mean the process of
allocating attention across time seems to be a really important process. Even the breakthroughs that you get with machine learning mostly
has to do with attention, is all you need is bot attention. Transformative bot attention. So attention is a really interesting one. - Yeah.
- But then like, yeah, how you allocate
that attention, again, is like, is at the core
of like what it means to be intelligent, what it
means to process the world, integrate all the important things, discard all the unimportant things. Attention is at the core of
it, it's probably at the core of memory too, because there's
so much sensory information, there's so much going on,
there's so much going on, to filter it down to almost nothing and just keep those parts. And to keep those parts and
then whenever there's an error to adjust the model such that
you can allocate attention even better to new
things that would result, maybe maximize the chance
of confirming the model or disconfirming the model that you have and adjusting it since then. Yeah, attention is a weird one. I was... I was always fascinated. I mean, I got a chance to
study peripheral vision for a bit and indirectly
studied attention through that. And it's just fascinating
how humans, how good humans are at looking around and
gathering information. - Yeah, at the same time people
are terrible at detecting changes that can happen. - Yes.
- In the environment. - Yes.
- If they're not attending in the right way, if their predictive model
is too strong, you know. So you have these weird things where like the machines can
do better than the people. It's not that it's like... You know, so this is
the thing is people go, "Oh, the machines can do this stuff that's just like humans." It's like, well the machines
make different kinds of mistakes than the people do. And I will never be convinced, unless I... That, you know, we've replicated human... I don't even like the term intelligence 'cause I think it's a stupid concept, but it's like I don't think
we've replicated human intelligence unless I
know that the simulator is making exactly the same kinds
of mistakes that people do. Because people make
characteristic mistakes, they have characteristic biases, they have characteristic
like, you know, heuristics that we use and those I
have yet to see evidence that ChatGPT will do that. - Since we're talking about attention, is there an interesting connection to you between ADHD and memory? - Well it's interesting for
me because when I was a child I was actually told... My school, I don't know if it came from a school psychologist, they
did do some testing on me, I know, for like IQ and stuff like that. Or if it just came from
teachers who hated me. But they told my parents that I had ADHD. And so this was of
course in the seventies. So basically they said like,
"You know, he has poor motor control and he's got ADHD." And so... And, you know, there were social issues. So like I could have been
put a year ahead in school but then they said, "Oh, but he doesn't have
the social intelligence. He doesn't have the social capabilities." - [Lex] Right. - So I still ended up being
like, you know, an outcast even in my own grade. But then like... So then my parents said, okay,
well they got me on a diet free of artificial colors and flavors, because that was the thing that people talked about back then. So I'm interested this topic because I've come to appreciate now that I have many of the characteristics, if not, you know, full blown. It's like I'm definitely
time blindness, rejection... I mean, you name it they talk about it. It's like impulsive behavior. I can tell you about all sorts
of fights I've gotten into in the past. Just you name it. But yeah, so ADHD is fascinating though because right now we're seeing like more and more diagnosis of it and I don't know what to say about that. I don't know how much of that is based on kind of inappropriate expectations, especially for children, and
how much of that is based on true kind of like
maladaptive kinds of tendencies. But what we do know is this,
is that ADHD is associated with differences in prefrontal function so that attention can be both more, you're more distractible,
you have harder time focusing your attention on what's relevant, and so you shift too easily. But then once you get on something that you're interested
in, you can get stuck. And so, you know, the attention
is this beautiful balance of being able to focus
when you need to focus and shift when you need to shift. And so it's that flexibility
plus stability again. And that balance seems
to be disrupted in ADHD. And so, as a result, memory
tends to be poor in ADHD, but it's not necessarily because there's a
traditional memory problem, but it's more because of
this attentional issue. Right? And so... And people with ADHD often
will have great memory for the things that they're interested in and just no memory for the things that
they're not interested in. - Is there advice from your
own life on how to learn and succeed from that? From just how the
characteristics of your own brain with ADHD and so on, how do you learn, how do you remember information? How do you flourish in this
sort of education context? - I'm still trying to figure
out the flourishing per se, but education, I mean, being in science is enormously enabling of ADHD. It's like you're constantly
looking for new things, you're constantly seeking
that dopamine hit. And that's great, you know. And they tolerate you're
being late for things. Nothing is really, nobody's
gonna die if you screw up. You know, it's just nice. It's not like being a doctor or something where you have to be like much
more responsible and focused. You can just freely follow your curiosity, which is just great. But what I'd say is, is
that like I'm learning now about so many things, like
about how to structure my activities more and basically say, "Okay, if I'm going to be..." Email's like the big one
that kills me right now, I'm just constantly like
shifting between email and my activities. And what happens is, is that I
don't actually get the email. I just look at my email and I get stressed 'cause I'm like, "Oh, I
have to think about this. Let me get back to it." And I go back to something else. And so I've just got fragmentary
memories of everything. Right? So what I'm trying to
do is set aside a time where like this is my email time, this is my, you know, writing time, this is my goofing off time, and so blocking these things off. Give yourself the goofing off time. Sometimes I do that. And sometimes I have to be flexible and go like, "Okay, I'm
definitely not focusing. I'm going to give myself the downtime." And it's an investment,
it's not like wasting time. It's an investment in
my attention later on. - And I'm very much with
Cal Newport on this, he wrote "Deep Work," and a
lot of other amazing books. He talks about task switching
as a sort of the thing that really destroys productivity. So like, you know, switching... Well it doesn't even
matter from what to what, but checking social media,
checking email, maybe switching to a phone call and then doing
work and then switching... Even switching between if
you're reading a paper, switching from paper to paper to paper. - Yeah.
- Because like curiosity and whatever the dopamine hit
from the attention switch, like limiting that 'cause
otherwise your brain is just not capable to
really like load it in and really do that deep
deliberation I think that's required to remember things and to
really think through things. - Yeah, I mean, you probably
see this, I imagine, in AI conferences, but definitely in
neuroscience conferences, it's now the norm that
people have their laptops out during talks and, you know,
conceivably they're writing, you know, they're writing notes. But in fact, what often
happens if you look at people, and we can speak from a little
bit of personal experience, is you're checking
email and you're like... Or I'm working on my own talk. But often it's like, you're doing things that are not paying... And I have this illusion,
"Well, I'm paying attention." And then I'm going back. And then what happens is
I don't remember anything from that day, it just kind of vanished. Because what happens is I'm creating all these artificial event boundaries. I'm losing all this executive function. Every time I switch, I'm getting
like a few seconds slower and I'm catching up mentally
to what's happening. And so instead of being in a model where you're meaningfully
integrating everything and predicting and generating
this kind of like rich model, I'm just catching up. You know? And so yeah, there's great
research by Molina Uncapher and Anthony Wagner on multitasking, that people can look up,
that talks about just how bad it is for memory and,
you know, it's becoming worse and worse of a problem. - So you're a musician, take me through how'd you get into music? Like what made you first
fall in love with music, with creating music? - I, yeah, so I started playing
music just when I was like doing trumpet in school for school band and I would just read music and play. And, you know, I was pretty decent at it. Not great, but I was decent. - How'd you go from trumpet to- - Guitar?
- To guitar? Especially the kind of music you're into? - Yeah, so basically in high school... Yeah, so I kind of was
a late bloomer to music, but just kind of MTV grew up with me. I grew up with MTV and so
then you started seeing all this stuff and then I got into... Metal was kind of like my early genre and I always reacted to
just things that were loud and had a beat like... I mean, ADHD, right? It's like, you know,
everything from "Sgt. Peppers" by The Beatles to like "Led
Zeppelin II," my dad had. My parents had both those albums, so I'd listen to them a lot. And then like The Police,
"Ghost in the Machine." But then I got into metal Def Leppard and, you know, AC/DC, Metallica, went way down the rabbit
hole of speed metal. And that time was kind of like, "Oh, like why don't I play guitar? I can do this." And I had friends who were doing that and I just never got it. Like I was, I took lessons
and stuff like that, but it was different because
when I was doing trumpet I was reading sheet music and this was like, I
was learning by looking. There's a thing called
tablature, you know this, where it's like you see like
a drawing of the fretboard with numbers and that's where
you're supposed to put your... It's kinda like paint by numbers, right? And so I learned it in a
completely different way, but I was still terrible
at it and I didn't get it. It's actually taken me a long time to understand exactly what the issue was. But it wasn't until I really got into punk and I saw bands, like I saw Sonic Youth, I remember especially,
and it just blew my mind because they violated the
rules of what I thought music was supposed to be. I was like, "This doesn't sound right, these are not power chords, and this doesn't just
have like a shouty verse and then a chorus part. It's not going back. This is just like weird." And then it occurred to me,
you don't have to write music the way people tell you
it's supposed to sound. That just opened up everything for me. And I was playing in a band and I was struggling with writing music because I would try to write like, you know, whatever
was popular at the time, or whatever sounded like other bands that I was listening to. And somehow I kind of
morphed into just like, just grabbing a guitar
and just doing stuff. And I realized a part of
my problem with doing music before was I didn't enjoy
trying to play stuff that other people played. I just enjoyed music
just dripping out of me and just, you know, spilling
out and just doing stuff. And so then I started to say, "What if I don't play a chord? What if I just play like notes
that shouldn't go together and just mess around with stuff?" Then I said, "Well what if
I don't do four beats going, nah, nah, nah, nah. One, two, three, four. One, two, three, four. One, two, three, four. What if I go one, two, three, four, five, one, two, three, four, five?" And started messing around
with time signatures. Then I was playing in this
band with a great musician who was really... Brent Ritzel, who was
in this band with me, and he taught me about arranging songs. And it was like, "What
if we take this part and instead of make it
go like back and forth we make it like a circle, or what if we make it like
a straight line, you know, or a zigzag, you know, just
make it like non-linear in these interesting ways?" And then the next thing you
know it's like the whole world sort of opens up as like the... And then what I started
to realize, especially... So you could appreciate
this as a musician, I think, so time signatures, right? So we are so brainwashed to
think in four four, right? Every rock song you can think
of almost is in four four. I know you're a Floyd fan, so think of "Money" by Pink Floyd, right? - [Lex] Yeah. (Charan vocalizing) - [Lex] Yeah. - You feel like it's in four four because it resolves itself, but it resolves on the last note of... Basically it resolves on the
first note of the next measure. So it's got seven beats instead of eight where the riff is actually happening. - [Lex] Interesting. - But you're thinking in four, because that's how we're used thinking. So the music flows a little bit
faster than it's supposed to and you're getting a little
bit of prediction error every time this is happening. And once I got used to that, I was like, "I hate writing at four four." Because I was like,
"Everything just feels better if I do it in seven four, or if I alternate between four and three." And doing all this stuff. And then it's like you just... And, you know, jazz music is like that. You know, they just do so much
interesting stuff with this. - So playing with those
time signatures allows you to like really break
it all open and just... I guess there's something
about that where it allows you to actually have fun. - Yeah, yeah. And it's like... So I'm actually like a very... One of the genres we used
to play in was Math Rock, was what they called it. It was just like, this has so
many weird time signatures. - What is math... Oh, interesting. - [Charan] Yeah, so. - That's the math part of
rock is what the mathematical disturbances of it, or what? - Yeah, I guess it would
be like, so instead of you might go like instead
of playing four beats in every measure... (Charan vocalizing) You go... (Charan vocalizing) You know? And that's just do these things. And then you might
arrange it in weird ways so that there might be three measures of verse and then one, you know, and then five measures of
chorus, and then two measures... So you could just mess
around with everything. Right? - What does that feel like to listen to? There's something about
symmetry, or like patterns, that feel good and like
relaxing for us or whatever. It feels like home. And disturbing that can
be quite disturbing. - Yeah.
- So is is that... Is that the feeling you
would have if you were keep messing with Math Rock? I mean, I- - Yeah, yeah.
- That's stressing me out just listening. - Well, yeah, yeah.
- Learning about it. - So, I mean, it depends. So a lot of my style of songwriting is very much like in terms
of like repetitive themes, but messing around with structure. 'cause I'm not a great
guitarist, technically, and so I don't play complicated stuff. And there's things that you can hear stuff where it's just like so
complicated, you know? But often what I find is,
is like having a melody and then adding some
dissonance to it, just enough, and then adding some complexity that gets you going just enough. But I have a high tolerance for that kind of
dissonance and prediction. I think, I have a theory, a pet theory, that it's like basically you can explain most of human behavior as
some people are lumpers and some people are splitters, you know? And so it's like some people are very kind of excited
when they get this dissonance and they wanna like go
with it, and some people are just like, "No, I wanna lump every..." You know, I don't know, maybe
that's even a different thing, but it's like, basically it's like, I think some people get
scared of that discomfort. - Yeah.
- And I really- - Thrive on it.
- Gravitate towards it. You know?
- I love it. What's the name of your band now? - The cover band I play in is
a band called Pavlov's Dogz. And so... - Yeah. - So it's a band, unsurprisingly, of mostly memory
researchers, neuroscientists. - I love this. - And so-
- I love this so much. - Yeah, actually one
of your MIT colleagues, Earl Miller plays bass. - He plays bass? So you play... Like, do you play with him, or- - So you could compete if you want. Maybe we could audition you. - For audition. Oh, yeah. I'm coming for you, Earl. (Charan laughing) - Earl's gonna-
- I'm coming for your spot. - Earl's gonna kill me. He is like very precise the way- - I'll play triangle or something. (Charan laughing) Or is it, a cowbell? Yeah, I'll be the cowbell guy. And you guys, what kind
of songs do you guys do? - So it's mostly late seventies
punk and eighties New Wave and post-punk Blondie, Ramones, Clash. I do, I sing "Age of Consent" by New Order and "Love Will Tear Us Apart." - [Lex] And you said you
have a female singer now? - Yeah, yeah, yeah. Kari Hoffman and also Paula Croxson. And so they do, they do, yeah. So Kari does Blondie amazingly well and we do like "Gigantic" by the Pixies. Paula does that one. - Which song do you love to play the most? What kind of song is super fun for you? - Of someone else's? - Yeah, a cover. Yeah. - A cover? Okay, and it's one we
do with Pavlov's Dogz? - [Lex] Mm-hmm. - I really enjoy playing,
"I Wanna Be Your Dog" by Iggy and The Stooges. - [Lex] Yeah, that's a good song. - Which is perfect 'cause
we're Pavlov's Dogz. - [Lex] Yeah. - And Pavlov of course was like, basically created learning theory. So, you know, there's that. But also it's like... But I mean Iggy and The
Stooges, that song, so I play and sing on it, but it's just like, it devolves into total noise and I just like fall on the
floor and generate feedback. I've like, I think in the last
version it might have been that or a Velvet Underground
cover in our last show. I actually, I have a guitar
made of aluminum that I got made and I thought this thing's indestructible and so I kind of like was just,
you know, moving it around, had it upside down and all this
stuff to generate feedback. And I think I broke one of the... I broke one of the tuning pegs and- - Oh, wow.
- Yeah, so I managed... I managed a break an all metal guitar. Oof, go figure. - A bit of a big ridiculous
question, but let me ask you, we've been talking about
neuroscience in general. What do you... You've been studying the
human mind for a long time. What do you love most
about the human mind? Like when you look at
it, we look at the FMRI, just the scans and the behavioral stuff, the electrodes, you know,
the psychology aspect, reading the literature
on the biology side, neurobiology, all of it. When you look at it, what is
most like beautiful to you? - I think the most beautiful but incredibly hard to put your finger on is this idea of the internal model. That it's like there's everything you see and there's everything you hear,
touch, and taste, you know, every breath you take, whatever, but it's all connected
by this like dark energy that's holding that whole universe of your mind together, right? And without that it's
just a bunch of stuff. And somehow we put that together and it forms so much of our experience. And being able to figure
out where that comes from and how things are connected
to me is just amazing. But just this idea of like
that the world in front of us, we're only sampling this little bit and trying to take so
much meaning from it. And we do a really good job. Not perfect, I mean, you know. But that ability to me is just amazing. - Yeah, it's an incredible
mystery, all of it. It's funny you said dark energy 'cause the same in astrophysics,
you look out there, you look at dark matter and dark energy, which is this loose
term assigned to a thing we don't understand, which
helps make the equations work in terms of gravity and the
expansion of the universe, in the same way. It seems like there's that
kind of thing in the human mind that we're like striving to understand. - Yeah, yeah. You know, it's funny
that you mentioned that. So one of the reasons I wrote the book, amongst many, is that I
really felt like people needed to hear from scientists. And like COVID was just
a great example of this, because like people weren't
hearing from scientists. One of the things I think
that people didn't get was the uncertainty of science
and how much we don't know. And I think every scientist lives in this world of uncertainty. And when I was writing the
book I just became aware of all of these things we don't know. And so I think of physics a lot and I think of this idea of
like overwhelming majority of the stuff that's in our universe cannot be directly measured. I used to think, "Ha ha,
I hate physics though." Physicists get the Nobel Prize for doing whatever stupid thing. It's like there's 10 physicists out there. I'm just kidding. Just-
- Strong words. - Yeah, no, no, no, I'm kidding. It's just the physicists
who do neuroscience can be rather opinionated so sometimes I like to dish on that. - [Lex] It's all love. - It's all love, that's right. This is the ADHD talking. So... But at some point I had this
aha moment where I was like to be aware of that
much that we don't know, and have a beat on it and
be able to go towards it, that's one of the biggest
scientific successes that I could think of. You are aware that you don't know about this gigantic section, overwhelming majority
of the universe, right? And I think the more what keeps me going to some extent is realizing
the changing the scope of the problem and figuring out, "Oh my God, there's all
these things we don't know." And I thought I knew this, 'cause science is all
about assumptions, right? So have you ever read "The Structure of Scientific
Revolutions" by Thomas Kuhn? - Yes.
- That's like my only philosophy really that I've read. But it's so brilliant in the
way that they frame this idea of like, he frames this
idea of assumptions being core to the scientific
process, and the paradigm shift comes from changing those assumptions. And this idea of like finding
out this kind of whole zone of what you don't know to me
is the exciting part, you know? - Well you are a great scientist and you wrote an incredible book. So thank you for doing that. And thank you for talking today. You've decreased the amount
of uncertainty I have, just a tiny little bit today, and revealed the beauty of memory. This was a fascinating conversation. Thank you for talking today. - Oh, thank you. This has been a blast. - Thanks for listening
to this conversation with Charan Ranganath. To support this podcast
please check out our sponsors in the description. And now let me leave you with some words from Haruki Murakami, "Most
things are forgotten over time, even the war itself. The life and death struggle
people went through is now like something
from the distant past. We're so caught up in our everyday lives that events of the past
are no longer in orbit around our minds, there
are just too many things we have to think about every day, too many new things we have to learn. But still, no matter how much time passes, no matter what takes place in the interim, there are some things we can
never assign to oblivion, memories we can never rub away. They remain with us
forever, like a touchstone." Thank you for listening, and
I hope to see you next time.