Brain ‘Washing’ During Sleep May Explain Why a Good Night’s Rest is so Important

“Brainwashing” is a term usually reserved for cults and other bad influences, not sleep. But new research indicates that your brain has the equivalent of a refreshing shower while you doze off. For years, the true purpose of sleep has baffled scientists, since there is little reliable data to support any of the prevailing theories.

That is, until recently.

A new study at the University of Rochester in New York claims to have concrete proof that the brain “washes” itself during sleep, essentially healing itself as you rest.

We know very little about sleep

We spend roughly a third of our lives asleep, and it seems as though that has remained fairly constant over the course of human history. That is, even though sleeping for so long makes humans vulnerable to predators of various sorts, we still remain near-helpless for a third of each day.

Science has not yet agreed on one main purpose for sleep, although previous studies have shown it regulates the metabolism and immune system. Because it takes up such a significant portion of our lives, many have long suspected that there’s a deeper biological process at work. Anything that would jeopardize our safety would probably be even more vital.

That’s what this new study suggests: sleep is a way to remove metabolic byproducts from the brain, meaning it could primarily be a method of recovery.

New imaging shows a brain “oil change”

When you go to sleep, so do your neurons, and blood will flow out of your head (possibly because “sleeping” neurons don’t need as much oxygen). Then, waves of cerebrospinal fluid (CSF) will enter the brain through tiny microchannels, pulsing through the tissue and “washing” your brain in waves. This is similar to how the lymphatic system works, so scientists nicknamed it the “glymphatic” system, thanks to its association of glial cells.

In awake people, the waves of CSF are small and seem to be synchronized to their breathing patterns. However, when they’re asleep, the waves of CSF are much larger. There seems to be a wave about once every 20 seconds during sleep.

In the study, scientists observed mice and the movement of CSF. They noticed that when the mice were asleep, the size of CSF channels in the brain expanded by about 60%. The research went on to inject the mice’s brains with proteins (a toxic kind associated with Alzheimer’s), then observe how fast the proteins were “washed” away. During sleep, the mice’s brains processed the proteins much faster.

The results pose additional questions, which need further research. For example, do the metabolic byproducts make us sleepy—do we need them to go to sleep? Does this “brain washing” actually improve the neurons’ function? The answers will further elucidate the exact purpose of sleep, which could help us solve both sleep disorders and perhaps even neurodegenerative diseases.

What can we learn from brain ‘washing’?

The idea that the brain might be “washing” or healing neurons during sleep poses an interesting link to neurodegenerative disorders such as Alzheimer’s. Many diseases in this category are associated with sleep dysfunction. If the brain is supposed to be “washing” itself during sleep but can’t, could that be a cause—or a symptom—of Alzheimer’s? Further research may shed light on better methods to treat these kind of diseases.

The science of sleep is still complex

One thing is for certain: we all need to get a healthy amount of sleep each night. The “right” amount varies per person (most adults need 7-9 hours, whereas developing children may need as many as 14).

Sleep doesn’t just “wash” your brain. Although that could be the primary function, it’s also responsible for a whole host of other benefits. For example, it helps us consolidate our memories, by taking our short-term memories and “transferring” them to the part of the brain that stores long-term memories. When you consider how rapidly child development takes place, it’s little wonder that it takes them longer to process the exponentially larger information load.

Your body also physically recovers while you sleep. Since you’re at rest, it’s the perfect time to repair muscle tissue, synthesize hormones and heal. When you deprive yourself of sleep, you’re cutting down on the time your body has to fight illness and injury—time you can’t get back. That’s why experts say “sleep debt” is real, and you can’t catch up on it.

As research and technology advance, we can look forward to learning how the complex science of sleep affects us all.