Results of the new study, funded by the National Institute of Neurological Disorders and Stroke (NINDS), part of the NIH, suggests that during sleep the brain is cleared of damaging molecules associated with neurodegeneration. Sleep changes the cellular structure of the brain. It appears to be a completely different state,” said Maiken Nedergaard, M.D., leader of the study. Not only is sleep important for storing memories, it may be also be the period when the brain cleanses itself of toxic molecules. It appears that during sleep a plumbing system called the glymphatic system opens, letting fluid flow rapidly through the brain. Glial cells help control the flow of cerebrospinal fluid (CSF), a clear liquid surrounding the brain and spinal cord, through the glymphatic system by shrinking or swelling. Since this appears to happen only during sleep, it highlights the critical importance of sleep in clearing the brain of toxins.