American scientists think they’ve discovered the function of sleep: to clear molecular buildup in the brain in what Guardian science reporter Ian Sample calls a “rubbish disposal service.”

Experiments on mice showed that during sleep, cerebral spinal fluid is pumped throughout the brain and flushes out waste products to the liver.

“The process helps to remove the molecular detritus that brain cells churn out as part of their natural activity, along with toxic proteins that can lead to dementia when they build up in the brain, the researchers say,” Sample reported.

Other researchers said more more work needs to be done to determine if the same process occurs in humans and whether creating an opportunity to clean the brain was sleep’s primary function.

— Posted by Alexander Reed Kelly.

Ian Sample at The Guardian:

Maiken Nedergaard, who led the study at the University of Rochester, said the discovery might explain why sleep is crucial for all living organisms. “I think we have discovered why we sleep,” Nedergaard said. “We sleep to clean our brains.”

Writing in the journal Science, Nedergaard describes how brain cells in mice shrank when they slept, making the space between them on average 60% greater. This made the cerebral spinal fluid in the animals’ brains flow ten times faster than when the mice were awake.

The scientists then checked how well mice cleared toxins from their brains by injecting traces of proteins that are implicated in Alzheimer’s disease. These amyloid beta proteins were removed faster from the brains of sleeping mice, they found.

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