Are we ‘brainwashed’ during sleep?

Summary: Study reveals as we sleep, cerebrospinal fluid pulses in the brain in rhythmic patterns.

Source: Boston University

New research from Boston University suggests that tonight while you sleep, something amazing will happen within your brain. Your neurons will go quiet. A few seconds later, blood will flow out of your head. Then, a watery liquid called cerebrospinal fluid (CSF) will flow in, washing through your brain in rhythmic, pulsing waves.

The study, published on October 31 in Science, is the first to illustrate that the brain’s CSF pulses during sleep, and that these motions are closely tied with brain wave activity and blood flow.

“We’ve known for a while that there are these electrical waves of activity in the neurons,” says study coauthor Laura Lewis, a BU College of Engineering assistant professor of biomedical engineering and a Center for Systems Neuroscience faculty member. “But before now, we didn’t realize that there are actually waves in the CSF, too.”

This research may also be the first-ever study to take images of CSF during sleep. And Lewis hopes that it will one day lead to insights about a variety of neurological and psychological disorders that are frequently associated with disrupted sleep patterns, including autism and Alzheimer’s disease.

The coupling of brain waves with the flow of blood and CSF could provide insights about normal age-related impairments as well. Earlier studies have suggested that CSF flow and slow-wave activity both help flush toxic, memory-impairing proteins from the brain. As people age, their brains often generate fewer slow waves. In turn, this could affect the blood flow in the brain and reduce the pulsing of CSF during sleep, leading to a buildup of toxic proteins and a decline in memory abilities. Although researchers have tended to evaluate these processes separately, it now appears that they are very closely linked.

To further explore how aging might affect sleep’s flow of blood and CSF in the brain, Lewis and her team plan to recruit older adults for their next study, as the 13 subjects in the current study were all between the ages of 23 and 33. Lewis says they also hope to come up with a more sleep-conducive method of imaging CSF. Wearing EEG caps to measure their brain waves, these initial 13 subjects were tasked with dozing off inside an extremely noisy MRI machine, which, as anyone who has had an MRI can imagine, is no easy feat.

“We have so many people who are really excited to participate because they want to get paid to sleep,” Lewis says with a laugh. “But it turns out that their job is actually–secretly–almost the hardest part of our study. 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.”

But for now, she is glad to have the opportunity to take images of CSF at all. One of the most fascinating yields of this research, Lewis says, is that they can tell if a person is sleeping simply by examining a little bit of CSF on a brain scan.

“It’s such a dramatic effect,” she says.

“[CSF pulsing 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.”

As their research continues to move forward, Lewis’ team has another puzzle they want to solve: How exactly are our brain waves, blood flow, and CSF coordinating so perfectly with one another? “We do see that the neural change always seems to happen first, and then it’s followed by a flow of blood out of the head, and then a wave of CSF into the head,” says Lewis.

This shows the CSF in the brain during sleep
During sleep, the brain exhibits large-scale waves: waves of blood oxygenation (red) are followed by waves of cerebrospinal fluid (blue), as reported in Fultz et al., Science, 2019. The image is credited to Laura Lewis, Boston University.

One explanation may be that when the neurons shut off, they don’t require as much oxygen, so blood leaves the area. As the blood leaves, pressure in the brain drops, and CSF quickly flows in to maintain pressure at a safe level.

“But that’s just one possibility,” Lewis says. “What are the causal links? Is one of these processes causing the others? Or is there some hidden force that is driving all of them?”

About this neuroscience research article

Boston University
Media Contacts:
Hilary Katulak – Boston University
Image Source:
The image is credited to Laura Lewis, Boston University.

Original Research: Closed access
“Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep”. Laura Lewis et al.
Science doi:10.1126/science.aax5440.


Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep

Sleep is essential for both cognition and maintenance of healthy brain function. Slow waves in neural activity contribute to memory consolidation, whereas cerebrospinal fluid (CSF) clears metabolic waste products from the brain. Whether these two processes are related is not known. We used accelerated neuroimaging to measure physiological and neural dynamics in the human brain. We discovered a coherent pattern of oscillating electrophysiological, hemodynamic, and CSF dynamics that appears during non–rapid eye movement sleep. Neural slow waves are followed by hemodynamic oscillations, which in turn are coupled to CSF flow. These results demonstrate that the sleeping brain exhibits waves of CSF flow on a macroscopic scale, and these CSF dynamics are interlinked with neural and hemodynamic rhythms.

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  1. This research is terribly misreported and misunderstood by the Neuroscience News writer. To interpret the scientific findings with “blood flows out and CSF flows in” gives the impression of replacing blood with CSF for a period to “rinse” the brain. The hemodynamic (blood) vasculature and cerebral spinal fluid are separate systems delineated by the blood-brain barrier (BBB). The scientists’ publication describes how these two systems work in concert during sleep (where neuronal activity is anything but quiet if you look at sleep EEG). Pretty good research that is poorly reported. Please use science writers that understand the area of science in which they are reporting. -from a PhD neuroscientist.

  2. First of all this is a very long subject but if you want to learn more type in “Craniosacral Therapy” into your search engine and you will begin to understand that this fluid that is in our bodies is what keeps us alive and “flows” in our bodies 24/7 except in the times (very rare and needing a guiding hand from a Craniosacral Ttherapist) that people can go into what is called “the still point” where healing can occur at a much deeper level.

    It is always being created by the third, fourth and lateral ventricles in the brain and flows from them all the way down to the tips of our toes and back up to the brain in a rhythmic motion that is referred to as “the tide” which has three different flow rates depending on how busy or how relaxed we are at any particular time of the day. This flow is what keeps all of the bodies systems functioning.

    If you want healing from physical, emotional traumas and other traumas like PTSD and other problems in the body which can begin from conception (acceptance and subsequent behavoral patterns especially from day 30 on or when the parents find out that they are pregnant) to birth (physical, emotional and drug induced) all the way to death these traumas (and many others like car accidents et al can produce like like headaches/migraines which can be removed from the body via “Craniosacral Therapy” and so peoples lives can be much better and more fullfilling without these traumas holding people back.

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