Allan Hamilton MD knows how brains work, in part, because he has drilled into thousands of them. A Harvard-trained brain surgeon, he’s also medical consultant to ABC’s Grey’s Anatomy and author of books including The Scalpel and the Soul and Zen Mind, Zen Horse. He’s now at work on a big book about the brain, and has shared a slice about how to protect that source of profound happiness called flow. Allanhamilton.com