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.
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.
They saw that cerebrospinal fluid appears to "synchronize" with brainwaves, which likely helps remove brain waste. This waste includes potentially toxic proteins that may otherwise form buildups that can impair the flow of information between neurons.
These findings, the researchers add, could also shed fresh light on the underlying mechanisms in conditions such as Alzheimer's disease, in which toxic protein plaques play a key role in memory loss and other cognitive impairments.
They also explain that normal aging may be associated with poorer self-cleaning in the brain. With age, human brains tend to generate fewer slow waves, which may reduce blood flow in the brain, as well as cerebrospinal fluid pulsations.
"It's such a dramatic effect," emphasizes Lewis. "[Cerebrospinal fluid pulsating in the brain during sleep] was something we didn't know happened at all, and now we can just glance at one brain region and immediately have a readout of the brain state someone's in."