Just like hunger, thirst, and sexual desire, the urge to sleep is a deep physiological drive. A growing number of experiments suggests the quantity and quality of your sleep directly affects many bodily processes, from hormonal balance to immune protection. These discoveries also reveal a strong link between sleep and improved mood, memory, and learning. Based on an article by Robert Stickgold, director of the Center for Sleep and Cognition at Beth Israel Deaconess Medical Center, this video explores the latest research into what happens when we sleep.