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Sleep Washes Your Brain

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While you sleep, your body repairs itself, and new evidence has demonstrated that sleeping washes away toxins in the brain as well.

Waves of cerebrospinal fluid (CSF) wash over the sleeping brain about every 20 seconds, delivering fresh CSF which moves harmful proteins out of the brain.  Some harmful proteins can go on to cause neurodegenerative disease like Alzheimer’s.

The study used MRI to scan healthy adults while they slept and used a form of functional MRI to measure the movements of CSF in the brain.  The fMRI revealed that the CSF was moving into the brain in a rhythmic pattern that resembles waves; but this isn’t the first time scientists have seen waves of CSF in the brain.  The difference was in the velocity of the waves during sleep.

When awake, CSF flows in very gentle waves that are associated with breathing patterns.  During sleep, however, the waves are much more powerful and larger.  The waves follow the brain’s electrical activity patterns:  first, in non-REM sleep, a slow wave due to nerve cell activity occurs, followed by a fall in oxygen levels due to the outflow of blood.  Then, the CSF wave replaces the blood that flowed out of the brain.

From previous animal studies, scientists have extrapolated that powerful waves of CSF in the brain of mice sweeps away amyloid-beta, which is the harmful protein which builds up and is related to Alzheimer’s disease.  This study highlights the importance of more studies on the sleeping human brain and how our brains benefit from a nightly clean.


  1. Fultz, Nina E., et al. “Coupled Electrophysiological, Hemodynamic, and Cerebrospinal Fluid Oscillations in Human Sleep.” Science, vol. 366, no. 6465, 1 Nov. 2019, pp. 628–631., doi:10.1126/science.aax5440.


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