Insulin, food intake, and reward.

Over the past three decades, the hormone insulin has been acknowledged to have multiple effects in the brain, and its role has been validated by the identification of receptors and a transport system for insulin in the central nervous system. Much research has focused on the action of insulin to participate in a feedback loop for the regulation of energy balance. Additionally, more recent studies are demonstrating effects of insulin on brain reward pathways; insulin can interact directly with limbic circuitry to decrease the rewarding or reinforcing value of experimental and natural stimuli, including food. These studies are reviewed in the context of current knowledge of insulin action in the brain, and we offer speculation regarding the relevance of this expanded role of insulin in mental disorders.