While animal and human studies indicate cognitive benefits from aerobic exercise across the lifespan, the great majority of controlled exercise studies in humans have been restricted to elderly individuals. Those studies have indicated that enhancing aerobic capacity has a beneficial effect on cognition. One study suggests that this benefit is seen particularly for executive control processes, precisely the processes affected by aging. These improvements have been accompanied by increases in gray matter density and changes in functional magnetic resonance imaging (fMRI) patterns of task-related activation. The goal of the proposed study is to extend the investigation of the beneficial effects of aerobic exercise to younger individuals, and to compare these effects in young and old.