One memorable Swedish study found that, among more than a million 18-year-old boys who joined the army, better fitness correlated with higher I.Q.'s, even among identical twins. Hoping to learn more about how fitness affects the developing brain, a recent study found that fit children had significantly larger basal ganglia, a key part of the brain that aids in maintaining attention and "executive control," or the ability to coordinate actions and thoughts crisply. Even more compelling is that aerobic exercise might just produce specific growth factors that stimulate the brain!
