The Importance of Sleep: Brain Flushes Out Toxins During the Night

Sleep may be more important than you may have thought. Scientists have discovered that a good night's rest may clear the mind--literally. The space between brain cells may increase during sleep, allowing the brain to flush out toxins that build up during waking hours. This could suggest why it's all-important to get a good night's sleep.

For years, scientists have wondered exactly why people sleep and how it affects the brain. Only recently have researchers been able to show that sleep is important for storing memories. In this latest study, though, researchers have also discovered another use for sleep; it may also be the period when the brain cleanses itself of toxic molecules.

In order to better understand how sleep might affect the brain, the researchers studied a plumbing system called the glymphatic system. They injected dye into the cerebrospinal fluid (CSF) of mice and watched it flow through their brains while simultaneously monitoring electrical brain activity. The dye flowed rapidly when the mice were unconscious--either asleep or anesthetized. In contrast, the dye barely flowed when the same mice were awake.

"We were surprised by how little flow there was into the brain when the mice were awake," said Maiken Nedergaard, one of the researchers, in a news release. "It suggested that the space between brain cells changed greatly between conscious and unconscious states."

In order to follow up with this discovery, the scientists then used electrodes inserted into the brain to directly measure the space between brain cells. It turned out that the space inside the brain increased by 60 percent when the mice were unconscious.

These findings reveal exactly how important sleep is. It can change the cellular structure of the brain, which could allow it to flush out toxins that build up during waking hours. Yet that's not all the study shows. It also could have larger implications for studies in the future.

"These results may have broad implications for multiple neurological disorders," said Jim Koenig, a program director at NINDS, in a news release. "This means the cells regulating the glymphatic system may be new targets for treating a range of disorders."

The findings are published in the journal Science.