Is sleep for rest? To conserve energy? For development? To cool the brain? To warm it? To boost the immune system? To learn and memorize? Or to unlearn, ridding our brains of excess mental baggage? All of these ideas have been proposed, leading to the suggestion that insomniacs might do better to count sleep theories instead of sheep. Join renowned neuroscientist Ralph Greenspan of The Neurosciences Institute to explore the latest research into the question of why we sleep.