New Study Shows That Sleep "Cleans the Brain".

A new study funded by the National Institute of Neurological Disorders and Stroke (NINDS) and published in Science shows that sleep increases the flow of cerebrospinal fluid in the brain which in turn flushes harmful waste proteins known as metabolites from the brain. Maiken Nedergaard, M.D., D.M.Sc.  professor of neurosurgery at the University of Rochester and an author of the study discovered the cleaning process while studying the brains of sleeping mice: dubbed the glymphatic system, it pumps cerebral spinal fluid (CSF) through the spaces around the brain cells, flushing waste into the circulatory system where it eventually makes its way to the liver.

Researchers studied the system by injecting dye into the CSF of mice and then observing it as it flowed through the brain using two-photon microscopy- a new imaging technology that allows scientists to see deep inside living tissue- while simultaneously monitoring electrical brain activity. The dye flowed rapidly when the mice were either asleep or anesthetized but barely flowed at all when the same mice were awake.

The researchers also discovered that during sleep brain cells contract, increasing the space between the cells by as much as 60 percent and allowing the spinal fluid to wash more freely through the brain tissue.

One of the waste products of the brain is the protein amyloid-beta, which accumulates and forms plaques in the brains of Alzheimer’s patients. Researchers at Washington University in St. Louis had previously shown that levels of amyloid-beta in mice brains dropped during sleep because of a decrease in production of the protein.“That was an observation that inspired our work,” says Nedergaard. Research in humans has shown that levels of amyloid-beta decline during sleep, as it does in mice, but it’s not yet known if the mechanisms are the same as in mice.

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References:
Maiken Nedergaard, M.D., D.M.Sc.
U.S. Department of Health and Human Services: The National Institutes of Health (NIH)
NPR: brains-sweep-themselves-clean-of-toxins-during-sleep
NBC News: good-nights-sleep-scrubs-your-brain-clean