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Discovering the Brain’s Nightly “Rinse Cycle”

Posted on by Dr. Francis Collins

Getting plenty of deep, restful sleep is essential for our physical and mental health. Now comes word of yet another way that sleep is good for us: it triggers rhythmic waves of blood and cerebrospinal fluid (CSF) that appear to function much like a washing machine’s rinse cycle, which may help to clear the brain of toxic waste on a regular basis.

The video above uses functional magnetic resonance imaging (fMRI) to take you inside a person’s brain to see this newly discovered rinse cycle in action. First, you see a wave of blood flow (red, yellow) that’s closely tied to an underlying slow-wave of electrical activity (not visible). As the blood recedes, CSF (blue) increases and then drops back again. Then, the cycle—lasting about 20 seconds—starts over again.

The findings, published recently in the journal Science, are the first to suggest that the brain’s well-known ebb and flow of blood and electrical activity during sleep may also trigger cleansing waves of blood and CSF. While the experiments were conducted in healthy adults, further study of this phenomenon may help explain why poor sleep or loss of sleep has previously been associated with the spread of toxic proteins and worsening memory loss in people with Alzheimer’s disease.

In the new study, Laura Lewis, Boston University, MA, and her colleagues at the Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston. recorded the electrical activity and took fMRI images of the brains of 13 young, healthy adults as they slept. The NIH-funded team also built a computer model to learn more about the fluid dynamics of what goes on in the brain during sleep. And, as it turns out, their sophisticated model predicted exactly what they observed in the brains of living humans: slow waves of electrical activity followed by alternating waves of blood and CSF.

Lewis says her team is now working to come up with even better ways to capture CSF flow in the brain during sleep. Currently, people who volunteer for such experiments have to be able to fall asleep while wearing an electroencephalogram (EEG) cap inside of a noisy MRI machine—no easy feat. The researchers are also recruiting older adults to begin exploring how age-related changes in brain activity during sleep may affect the associated fluid dynamics.


[1] Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Fultz NE, Bonmassar G, Setsompop K, Stickgold RA, Rosen BR, Polimeni JR, Lewis LD. Science. 2019 Nov 1;366(6465):628-631.


Sleep and Memory (National Institute of Mental Health/NIH)

Sleep Deprivation and Deficiency (National Heart, Lung, and Blood Institute/NIH)

Alzheimer’s Disease and Related Dementias (National Institute on Aging/NIH)

NIH Support: National Institute of Mental Health; National Institute of Biomedical Imaging and Bioengineering; National Institute of Neurological Disorders and Stroke


  • Lorraine says:

    I could see the video. It sounds interesting.

  • Sheila says:

    Will Dr. Lewis be recruiting people with post concussion syndrome?

  • Richard Smith says:

    I would love to see blood flow as a function of problem solving, for example, does it have regular periodicity, or might a requirement for deep thought change its pace? This could be extended to other functions having reflexive vs considered reactions, differences among people based on thought-problem solving, etc. Some things might be dicey to model in fMRI…

  • Renee says:

    I’m interested in the study. How do I find out more?

  • M. Bryant says:

    I would live to see the brains of people with serious insomnia.

  • RLLAnders says:

    I have some personal observations about AQP4. Can observe when it shuts off and turns on. Wonder if there is a correlation. Wonder what parts of the blood are involved in this process, specifically. Have been studying about fluid dynamics and flow in the brain and think it’s fascinating. This is amazing research!


    The entire scientific team deserves an applause with critical research appreciation for elegantly devising, conducting, executing, interpreting and presenting the neuronal-networks-sleep-wake cycles-brain waves alongwith the glymphatic system; water-channels primarily aquaporins and metabolic flux/biochemical neuronal signaling-mediated target genes’ activation warrant future global collaborative research efforts with replication of the current data-sets in human subjects, both healthy controls and age-matched cases of varying genetic landscapes.
    Moreover, efforts shoud be strategically developed to safeguard the confidentiality of pilot data-sets in such novel, thought-provoking experiments so that the scientific/clinical research team may successfully present their meticulous research findings to a global audience without instances of plagiarism, breach of privacy, scientific misconduct by contemporaries vying for federal grants in same/similar fields in the ever-expanding biomedical sciences/public health research!
    Overall, an excellent nightlife-depiction of the complex brain-waveforms!!!

  • C Whitla says:

    I have chronic insomnia for some years and have noticed a marked deterioration in memory recall, working memory and thought processing. I also have Hydrocephalus (VP Shunted) and I have known about the CSF rhythmic “washing” of the brain for some time as I read about it elsewhere (forget exactly). The regular pulsing of the CSF in sleep is NOT connected to the regular blood pulse but seems to be on a separate timescale on its own (as you mentioned, it took approx 20 seconds). Also, it has been postulated that, during sleep, the glial cells of the brain parenchyma gently separate the neurons etc to allow the CSF to flush between the neurons, including the synaptic gap. This cleanses the brain of toxins as well as flushes unwanted neurotransmitters from the gap and “resets” the brain for a new day. This may explain why depression (serotonin related) follows (or is concomitant with) periods of poor sleep (also serotonin related). Perhaps the brain is not being sufficiently cleansed of serotonin, resulting in a down-regulation of serotonin transmitters (5HTT)? Or is there another blockage taking place? With the advent of electronic screens interrupting our sleep cycles, this may account (partially or wholly) for our increasing occurrence of depression in society and, in particular, among young people?

    I would love to know your thoughts. Thank you for a good article – very thought provoking.

  • Magster says:

    24/7 tinnitus is linked to many diseases – and a new MRI study shows those of us who suffer with it may be sleeping – but part of our brain is actually “alert” and therefore we are not totally asleep. I’d like to know more about that. When I wake from dreams my first sensation is ringggggg- hissssss. When I wake up in the morning it’s soooo loud 🙁. Started 3 yrs ago after bout of flu.

  • Mary M J says:

    Anyone have thoughts on this cleansing process and the fluctuation of glutamate levels possibly causing intermittent seizures? I’ve spent years working on healing my daughter seizures and we’re down to only night times, not every night and just one or two in the same night. The unique aspect is my daughter is not regressing in skills from these nighttime seizures but actually seems more clear the next day.

  • Bernie says:

    Very interesting approach also for migraineurs. Investigation shouldn’t only search for the reasons of migraines. The key could be to find the conditions in the body which stop a migraine episode. I have episodic migraines for more then 50 years without aura. I noticed always that sleep is not = sleep. Sometimes sleeping 8 h do not change anything during an attack, I wake up at the same point where I felt asleep and pain didn’t change. But sometimes a clearing, relaxing sleep-cycle has a very repairing effect.
    Also, taking a triptan (serotonin) can have from no effect while going on with normal activity to high effect combined with a profound sleep-cycle. And in my case, the duration of sleep seems no to matter.

  • Steve says:

    “people who volunteer for such experiments have to be able to fall asleep while wearing an electroencephalogram (EEG) cap inside of a noisy MRI machine—no easy feat.”
    For sure, no easy feat, and probably next to impossible for an insomniac until serious exhaustion has set in! Perhaps the results were based upon the brain constantly scanning for the impending rat-a-tat-tat from the MRI machine. It would be interesting to see if similar results occurred with a deaf person.

  • Lori says:

    I have narcolepsy which I’m being managed & medicated for. Regardless, I often must go without sleep when caring for my special needs child. At this point my typical sleep is 4-6 hours nightly. I’m scared to death of what I’m doing to myself

  • Joanne M. Gallagher, RCST says:

    Incredible! We are now beginning to “see” a moment of the “Breath of Life” as described by Dr. William H. Sutherland with the cranial concept of Osteopathy, now taught with the Biodynamic Craniosacral curriculum.

    He also wrote about an invisible element contained within the cerebral spinal fluid which he referred to as, “Breath of Life.” He asked his students to visualize this Breath of Life as a fluid within the cerebral spinal fluid, something that has potency, which makes the fluid move with tidal motions. “Visualize a potency, an intelligent potency, that is more intelligent than your own human mentality.”

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