When I was about to turn 40, I started working out regularly after years of inactivity. As I sweated my way through cardio, weights, and dance classes, I noticed that exercise wasn’t just changing my body. It was also profoundly transforming my brain—for the better. The immediate effects of exercise on my mood and thought process proved to be a powerful motivational tool. And as a neuroscientist and workout devotee, I’ve come to believe that