Everyone agrees that there are many benefits to sleep, but there may be more to sleep than researchers have yet cataloged. A study from the University of Rochester Medical Center’s Center for Translational Neuromedicine has contributed to the body of work that supports the importance of sleep. The researchers found that during sleep, the brain may be able to cleanse itself of toxic molecules. This could change how neurological disorders are studied and treated.

The researchers stumbled onto this finding during a study of the glymphatic system—the central nervous system’s sewage mechanism—in mice. By injecting the mice’s cerebrospinal fluid (CSF) with a dye, the researchers were able to observe the movement of CSF in the brain. They noticed that when the mice were asleep, the dye flowed rapidly, but when the mice were awake, it moved slowly. According to Dr. Maiken Nedergaard, one of the study’s leaders, this “suggested that the space between brain cells changed greatly between conscious and unconscious states.”

Determined to learn more, the researchers inserted electrodes into the mice’s brains to measure the change in space between brain cells. They found a huge variation: the space between cells increased by 60% when the mice were asleep or anesthetized.

The team ran two more tests. First, they treated conscious mice with drugs that block noradrenaline (a hormone that controls cell volume). This induced sleep and increased the flow of fluid between the cells. These results helped to substantiate the link between sleep and the glymphatic system. For the second test, the researchers built upon previous research that demonstrated toxic molecules related to certain neurogenerative disorders build up between brain cells. The researchers injected the mice with a protein associated with Alzheimer’s (radiolabeled beta-amyloid) and measured how long it stayed in the brains while the mice were asleep or awake. The protein dissipated faster when the mice were asleep, indicating that one of the benefits of sleep is the removal of toxins from the brain.

Dr. Jim Koenig, a program director from National Institute of Neurological Disorders, which funded the study, commented, “These results may have broad implications for multiple neurological disorders.”

This research is published in the journal Science.

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