The brain washes out toxins as we sleep

The brain washes out toxins during sleep, including proteins related to Alzheimer’s disease, researchers have found. They showed in mice that the space between brain cells grows larger during sleep, allowing the brain to flush out substances it doesn’t need.

“Sleep changes the cellular structure of the brain. It appears to be a completely different state,” said Maiken Nedergaard, M.D., University of Rochester Medical Center in New York, a leader of the study.

Published October 2013 in Science, study results show that during sleep a “plumbing” system called the glymphatic system opens, allowing fluid to flow rapidly through the brain. The glymphatic system helps control the flow of cerebrospinal fluid, a clear liquid surrounding the brain and spinal cord.

Researchers studied the glymphatic system by injecting dye into the cerebrospinal fluid of mice and watching it flow through their brains while monitoring electrical brain activity. The dye flowed rapidly when the mice were unconscious, but the dye barely flowed when the same mice were awake.

Researchers were surprised to find that the space between brain cells can increase up to 60 percent when the mice were asleep. “It’s like a dishwasher that keeps flushing through to wash the dirt away,” Nedergaard said in a September 2014 Time magazine article.

There are implications for Alzheimer’s disease research. Researchers injected the mice with a protein associated with Alzheimer’s disease and measured how long it lasted in their brains when they were asleep or awake. It disappeared faster when the mice were asleep, “suggesting sleep normally clears toxic molecules from the brain,” the National Institutes of Health said.

While this study involved mouse brains, Nedergaard said the flushing system also is in dogs and baboons, and the next step is to look for it in human brains.

The results also highlight the importance of sleep, and the connection between sleep and overall health.

“We need sleep. It cleans up the brain,” Nedergaard said.