Scientists have long known and theorized how our sleep cycle helps heal our brain and bodies. We’ve talked about it too – there are even light and sound brain treatments designed to slow down the progression of Alzheimer’s.
A new piece of the puzzle has been uncovered by Laura Lewis and her team of researchers from the Boston University Lab. The study was published in the journal Science in which they detailed how our bodies clear toxins out of our brains when we sleep.
Sleep cycles are a well-documented phenomenon at this point. As we fall asleep, our brains move through several different phases from light sleep, through REM sleep which is characterized by dreams and rapid eye movement, too deep, dreamless slumber.
Lewis’ work focused on the deeper non-REM sleep which happens earlier in the night and which scientists had already associated with memory retention. In doing so, they observed how, in our sleep, waves of cerebrospinal fluid washed away toxin build-up from our brains. Some such toxins include beta amyloid which has been shown to trigger Alzheimer’s disease. Another such toxin is tau, a protein that harms the connections of our neurons.
This process had previously been observed in rodents in 2013 and was strongly suspected in people as well. The cerebrospinal fluid is a water-like liquid that surrounds our brain. As we sleep, Laura discovered, electrical impulses push waves of this fluid around our brains, helping it to quite literally wash away the toxins from it.
How did the Boston University researchers establish this?
To research sleep’s effect on our brains, Lewis and her team used the help of volunteers who came to sleep in their lab. The study participants were asked to lie down inside an MRI machine and fall asleep in it. Participants were asked to stay up a bit late the night before so that they could have an easier time falling asleep in the lab.
As the participants were making themselves “comfortable” inside the MRI machine, the researchers also outfitted them with EEG caps to help them monitor the electrical currents inside the participants’ brains. Meanwhile, the MRI was observing the blood oxygen levels and showed the movement of the cerebrospinal fluid.
“We had a sense each of these metrics was important, but how they change during sleep and how they relate to each other during sleep was uncharted territory for us,” Lewis said.
Naturally, all the research took place in the dead of night. Lewis herself wasn’t oblivious to the humor in the whole situation – while researching the importance of sleep to prevent Alzheimer’s disease, she and her team had to suffer through countless sleepless nights.
“It’s this great irony of sleep research,” Lewis says. “You’re constrained by when people sleep.”
The fruit of all these sleepless nights was the conclusion that during non-REM sleep large and slow-moving waves of cerebrospinal fluid are indeed moving through our brains. The EEG helped show this by observing the synchronization of neurons in our brains, turning on and off again to trigger the fluid’s waves.
“First you would see this electrical wave where all the neurons would go quiet,” said Lewis. This synchronization is vital since when the neurons stop firing in unison, they require less oxygen. That, in turn, means less blood flow to the brain which allows the cerebrospinal fluid to rush in. It’s that synchronization that creates the necessary waves of the fluid, allowing it to better clean our brains.
The discovery has been lauded by scientists from the field, including by Maiken Nedergaard, the neuroscientist from the University of Rochester who established the similar process in the brains of mice.
“It’s a fantastic paper,” said Maiken Nedergaard. “I don’t think anybody in their wildest fantasy has really shown that the brain’s electrical activity is moving fluid. So that’s really exciting.”
Lewis’ team’s confirmation on Nedergaard’s experiments proves a lot of what we’ve been theorizing up until now. It also shows why people with irregular sleep patterns are shown to be much more susceptible to Alzheimer’s.
“It’s telling you sleep is not just to relax,” said Nedergaard. “Sleep is actually a very distinct function.”
Lewis’s discovery means more than just a better understanding of our sleep. It paves the way for the development of more effective Alzheimer’s and dementia medication. Drugs were already being developed for treating beta amyloid but many recent trials have failed.
“This opens a new avenue,” explains Nedergaard. This discovery can lead to other approaches that don’t just try to target the toxins themselves but improve our brain’s ability to get rid of them on its own.
“Aging is not just about one molecule,” says Nedergaard. “Everything fails.”
Of course, much more research can and should be done as well. Lewis’s team focused only on one stage of our sleep, for example, so the whole cycle may still hold other secrets worth knowing.
Thankfully, the methods the Boston University researchers used are perfectly noninvasive so further research should be on the way too. This may mean more sleepless nights for Lewis and her team but it may also mean better and more effective treatment and prevention of Alzheimer’s disease.