Medical News Today: How waste gets 'washed out' of our brains during sleep

For the first time, a new study has observed that cerebrospinal fluid washes in and out of the brain in waves during sleep, helping clear out waste.
person asleep in bed
Cerebrospinal fluid helps clear toxic waste from the brain during sleep.

Recently, Medical News Today reported on a study that found that specialized immune cells are more active in the brain during sleep, busy performing maintenance work.

Researchers know that sleep is important — not just in terms of allowing the brain to reactualize, but also for "making space" for "cleaning" processes to take place.

However, many of the mechanisms through which this clearing out of brain waste takes place during sleep remain unclear.

Now, researchers at Boston University in Massachusetts have found that during sleep, the fluid present in the brain and spinal chord — called the cerebrospinal fluid — washes in and out, like waves, helping the brain get rid of accumulated metabolic "trash."

"We've known for a while that there are these electrical waves of activity in the neurons. But before now, we didn't realize that there are actually waves in the cerebrospinal fluid, too," study co-author Laura Lewis explains.
A complex synchronization process

The new study — the results of which appear in the journal Science — included 13 participants ages 23–33 who agreed to undergo brain scans while asleep.

The process was a tricky one. The participants had to wear EEG caps that allowed the researchers to measure electrical activity in their brains while lying in an MRI machine, where they were meant to sleep.

However, sleeping in this location can be difficult, as MRI machines are very noisy. "[I]t turns out that [the participants'] job is actually — secretly — almost the hardest part of our study," says Lewis.

"We have all this fancy equipment and complicated technologies, and often a big problem is that people can't fall asleep because they're in a really loud metal tube, and it's just a weird environment," she notes.