" Movement places demands on the brain, just as it does on muscle, and so the brain releases BDNF, which triggers the growth of cells to meet the increased mental demands of movement. But BDNF floods throughout the brain, not just to the parts engaged in movement. Thus, the whole brain flourishes as a result of movement. It provides the environment that brain cells need to grow and function well. Chemically, there is more to this story—lots "

― John J. Ratey , Go Wild: Free Your Body and Mind from the Afflictions of Civilization