Sleep may help clean the brain, study says

LOS ANGELES — When we sleep, our brains get rid of gunk that builds up while we are awake, suggests a study that may provide clues to treat Alzheimer’s disease and other disorders.

This cleaning was detected in the brains of sleeping mice, but scientists said there is reason to think it happens in people, too.

If so, the finding may mean that for people with dementia and other mind disorders, ‘‘sleep would perhaps be even more important in slowing the progression of further damage,’’ Dr. Clete Kushida, medical director of the Stanford Sleep Medicine Center, said in an e-mail. Kushida did not participate in the study, which appears in Friday’s issue of the journal Science.


People who do not get enough sleep have trouble learning and making decisions and are slower to react. But despite decades of research, scientists cannot agree on the basic purpose of sleep. Reasons range from processing memory to regulating the body.

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The latest work, led by scientists at the University of Rochester Medical Center, adds fresh evidence to a long-standing view: When we close our eyes, our brains go on a cleaning spree.

The team previously found a plumbing network in mouse brains that flushes out cellular waste. For the new study, the scientists injected the brains of mice with beta-amyloid, a substance that builds up in Alzheimer’s disease, and followed its movement. They determined that it was removed faster from the brains of sleeping mice than awake mice.

The team also noticed that brain cells tend to shrink during sleep, which widens the space between the cells. This allows waste to pass through that space more easily.