More than 20 years ago, two philosophers, Andy Clark and David Chalmers, wrote a journal article that opened with a question: “Where does the mind stop and the rest of the world begin?” Now, that question would seem to have an obvious answer, right? The mind stops at the head. It’s contained within the skull. But Clark and Chalmers maintained that

The mind is generally associated with feelings, sentience, and consciousness of self, while the brain is a dissectible biological tissue. But learning about the brain, which is part of a larger system called the nervous system, can teach us about the mind and thus about our nature.