In findings that give fresh meaning to the old adage that a good night’s sleep clears the mind, a new study from the University of Rochester shows that a recently discovered system that flushes waste from the brain is primarily active during sleep. This revelation could transform scientists’ understanding of the biological purpose of sleep and point to new ways to treat neurological disorders.
Maiken Nedergaard, M.D., D.M.Sc., co-director of the University of Rochester Medical Center’s Center for Translational Neuromedicine and lead author of the article, said the study shows that the brain has different functional states when asleep and when awake.
The study, which was published last month in the journal Science, reveals that the brain’s unique method of waste removal—dubbed the glymphatic system—is highly active during sleep, clearing away toxins responsible for Alzheimer’s disease and other neurological disorders. Furthermore, the researchers found that during sleep the brain’s cells reduce in size, allowing waste to be removed more effectively.
“The brain only has limited energy at its disposal and it appears that it must choose between two different functional states—awake and aware or asleep and cleaning up,” said Nedergaard. “You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.”
The study also found that the cells in the brain “shrink” by 60 percent during sleep. This contraction creates more space between the cells and allows cerebral spinal fluid to wash more freely through the brain tissue.
“These findings have significant implications for treating ‘dirty brain’ disease like Alzheimer’s,” said Nedergaard. “Understanding precisely how and when the brain activates the glymphatic system and clears waste is a critical first step in efforts to potentially modulate this system and make it work more efficiently.”