Burning the candle at both ends for a week may take an even bigger toll than you thought. Researchers at the University of Wisconsin-Madison have found that five nights of restricted sleep--four hours a night--affect the brain in a way similar to that seen after acute total sleep deprivation. The new study in rats, appearing in the current online edition of the Proceedings of the National Academy of Sciences, adds to the growing evidence scientists are accumulating about the negative effects of restricted sleep for both the brain and the body. "There's a huge amount of interest in sleep restriction in the field today," says Dr. Chiara Cirelli, associate professor of psychiatry at the School of Medicine and Public Health, who led the research. Many people are sleep restricted, either because they have to or because they choose to be, she says.