 The philosopher’s conception of personal identity refers to the issue of what makes a person at one time numerically identical to a person at another time. This metaphysical question has been addressed by a variety of philosophical theories. For example, some theorists argue that what it is to be the numerically identical over time is to be the same human organism (Olson, 1999), and that being the same organism is determined by sameness of life. If having the same life is the relevant criterion, one could argue that life-sustaining areas of the brainstem are essential to personal identity (Olson, 1999). For those who believe instead that bodily integrity is what is essential, the ability of neuroscience to alter the brain will arguably have little effect on personal identity. Many other philosophers have identified the same person as being grounded in psychological continuity of some sort (e.g., Locke). If this criterion is the correct one, then the stringency of that criterion may be crucial: radical brain manipulation may cause an abrupt enough shift in memories and other psychological states that a person after brain intervention is no longer the same person he or she was prior. The more stringent the criterion, the greater is the potential threat of neurotherapies to personal identity (Jecker and Ko, 2017; Pascalev et al. 2016). On the other hand, if the standards for psychological continuity or connectedness are high enough, changes in personal identity may in fact be commonplace even without neurotherapies. Recognizing this may prompt us to question the criterion and/or the importance or value of personal identity. Parfit, for example, argues that what makes us one and the same person over time, and what we value (psychological continuity and connectedness) come apart (Parfit, 1984).