In our Cerebrum article, "The Sleeping Brain," sleep researchers Chiara Cirelli and Giulio Tononi write about what happens inside our brains when we sleep. In our related podcast with Cirelli, M.D., Ph.D., a professor in the Department of Psychiatry at the University of Wisconsin, the sleep researcher talks about the difference between sleep and rest, the impact of sleep on memory, different sleeping habits, and the ties between nutrition and sleep. She also tells us what we've learned from sleep research and what we still need to know.