So exactly, how does a lack of sleep impact our emotional brain? Why does that lack of sleep make us so emotionally irrational and hyperreactive? [Sleeping with Science] Well, several years ago, we conducted a brain imaging study. And we took a group of healthy adults. And we either gave them a full night of sleep or we sleep-deprived them. And then the next day, we placed them inside an MRI scanner, and we looked at how their emotional brain was reacting. And we focused on one structure in particular, it's called the amygdala. And the amygdala is one of the centerpiece regions for the generation of strong emotional reactions, including negative emotional reactions. Now when we looked at those people who had had a full night of sleep, what we saw was a nice, appropriate moderate degree of reactivity from the amygdala. It wasn't as though there was no response at all, but it was an appropriate response. Yet in those people who were sleep-deprived, that deep emotional brain center was in fact, hyperactive. Indeed, the amygdala was almost 60 percent more responsive under conditions of a lack of sleep. But why was that the case? And what we went on to discover, is that there's another brain region that's involved. This brain region is called the prefrontal cortex, and it sits directly above your eyes. And you can think of the prefrontal cortex almost like the CEO of your brain. It's very good at making high-level, executive, top-down control decisions and reactions. In fact, it's one of the most evolved regions of our brain. And one of the parts of the brain that it controls is this deep emotional center, the amygdala. Now in those people who had had a full night of sleep, there was a nice, strong communication and connection between the prefrontal cortex, regulating that deep emotional brain center. But in those people who were sleep-deprived, that communication, that connection between the prefrontal cortex and that deep amygdala emotional brain center had essentially been severed. And as a consequence, the amygdala was responding far more reactively due to a lack of sleep. It's almost as though without sleep we become all emotional accelerator pedal, and too little regulatory control brake. And that seems to be the reason that we become so unbuckled in terms of our emotional integrity when we haven't been sleeping well. So that's the bad that can happen if I take sleep away from you. But it turns out that there's something good that happens when you get your sleep back. And sleep, particularly rapid eye movement sleep, actually offers a form of emotional first aid. Because it's during sleep at night that we take these difficult emotional experiences that we've been having during the day, and that sleep acts almost like a nocturnal soothing balm, taking the sharp edges off those difficult experiences. And so perhaps it's not time that heals all wounds, it's time during sleep that provides that form of emotional convalescence. So that when we come back the next day, we're able to cope with those emotional memories.