Researchers measured how long the dye lasted in the brain when the mice were asleep versus awake. They found that the dye flowed rapidly through mice brains when the mice were unconscious, either asleep or anesthetized. In contrast, the dye barely flowed when the same mice were injected with labeled beta-amyloid, a protein associated with Alzheimer’s disease. Beta-amyloid disappeared faster in mice brains when the mice were asleep, suggesting sleep normally clears toxic molecules from the brain. “These results may have broad implications for multiple neurological disorders,” said Jim Koenig, Ph.D., a program director at NINDS. It also suggests a new role for sleep and may highlight the critical importance of sleep for prevention as well as healthy on-going brain care. “We need sleep. It cleans up the brain,” said Maiken Nedergaard, M.D., D.M.Sc., co-director of the Center for Translational Neuromedicine at the University of Rochester Medical Center in New York, and a leader of the study.