In "Spark," John J. Ratey explains how exercise is crucial not just for physical health but for mental clarity as well. The book outlines compelling scientific evidence showing that physical activity sparks biological changes that increase brain function and improve mental health. Ratey details how exercise can help manage conditions like depression, ADHD, and addiction, and enhance functions like decision-making and focus. "Spark" offers an in-depth look at the mind-body connection, advocating exercise as a powerful remedy for the brain.