Steve and Corey talk to Jason about a fundamental question of neuroscience: Do humans grow new neurons as adults? The dogma that humans do not, gave way to the dogma that they do, which is now being questioned. Adult neurogenesis has been associated with learning, better cognitive function and resistance to depression. Jason suggests that a simple error of treating young mice as models for adult humans led to excessive optimism regarding the potential for later neuronal growth. Recent findings suggest that adults grow few, if any, new neurons but that what little neurogenesis occurs can probably be enhanced by exercise.