You probably know that getting a good night's sleep is important to your health. Sleep helps you stay alert; it reduces your risk of diabetes; and it can prevent weight gain. It can even make you kinder.

What you may not know is that sleep gives your brain's maintenance crew the opportunity to clean up.

Sleep helps the brain rid itself of the cellular refuse that contributes to neurodegenerative diseases like Alzheimer's and Parkinson's.

Brain cells require fuel, and they leave metabolic waste in the process. That's what gets cleared away while you sleep.

We know more about how this brain cleaning team works thanks to a recent study.

It may seem odd that the brain is at work when we are at rest, but when you think about it, it makes sense. When we are asleep, the brain is not involved in the sorts of tasks that absorb its energy and attention while we are awake — things like remembering what to buy at the store, planning a trip or driving home.

In order to perform such energy-demanding tasks, brain cells require fuel, and they leave metabolic waste in the process. That's what gets cleared away while we sleep.

“We knew that sleep is a time when the brain initiates a cleaning process to flush out waste and toxins it accumulates during wakefulness. But we didn't know how that happens,” Jonathan Kipnis, the senior author of the study showing how the brain rids itself of debris, said in a statement.

The Washington University School of Medicine researchers uncovered how the process works in mice. During sleep, neurons in the brain produce bursts of electrical pulses that build to produce rhythmic waves. These waves propel fluid through dense brain tissue, washing the waste tissue out in the process.

The process may be similar to washing dishes: After an initial rinse, a more focused cleansing takes place.

“These neurons are miniature pumps. Synchronized neural activity powers fluid flow and removal of debris from the brain,” explained the first author of the study, Li-Feng Jiang-Xie, a postdoctoral research associate in the Kipnis Lab.

Because the brain is dense, cleaning it is not easy. Cerebrospinal fluid surrounding the brain enters and weaves through intricate cellular webs, collecting toxic waste as it travels and then exits the brain, spilling its contaminated fluid into the outer tissue layer enveloping the brain underneath the skull.

The process became apparent when the team silenced specific regions in the brains of sleeping mice so that neurons in those regions couldn't fire the coordinated electrical signals that generate rhythmic waves in the brain. Having done this, they found that cerebrospinal fluid in those areas was unable to flow and so trapped waste couldn't leave the brain tissue.

“We think the brain-cleaning process is similar to washing dishes,” Jiang-Xie explained. “You start, for example, with a large, slow, rhythmic wiping motion to clean soluble wastes splattered across the plate. Then you decrease the range of the motion and increase the speed of these movements to remove particularly sticky food waste on the plate.”

Brain wave patterns change throughout our sleep cycles. Taller brain waves with larger amplitude move fluid with more force. The researchers hope to look into why neurons fire waves with varying rhythmicity during sleep and understand the regions of the brain that are prone to waste accumulation in future studies.

“If we can build on this process, there is the possibility of delaying or even preventing neurological diseases, including Alzheimer's and Parkinson's disease, in which excess waste — such as metabolic waste and junk proteins — accumulate in the brain and lead to neurodegeneration,” said Jiang-Xie.

The study is published in Nature.