Professor of the Practice of Law University of Denver Sturm College of Law

Sleep Clears Waste from Brain

Research on rodents has shown that they experience glymphatic brain clearance of cerebrospinal fluid (CSF) during sleep.  Vasomotor (in the arterial wall), respiratory (in the veins), and cardiac (arterial pulse) pulsations drive CSF flow that clears waste from the brain.

Researchers monitored vasomotor, respiratory, and cardiac brain pulsations during sleep by recording fast fMRI, magnetic resonance encephalography (MREG), and electroencephalography (EEG) signals in 15 healthy volunteers (age 22-30, 6 females).  During sleep, vasomotor and respiratory rhythms intensified and became more stable.  Smaller cardiac pulse increases were detected in the smallest areas of the brain. 

The respiratory pulsation increases were greatest in the visual, auditory, and sensorimotor areas of the thinking brain, parts of the cortex that we use the most during the day.  Researchers believe these areas are the most important to clear of waste from as we sleep. 

A decrease in brain pulsations and waste clearance precedes the accumulation of beta-amyloids, typically found in the brains of patients with Alzheimer’s disease.

Takeaway:  This study supports the theory that fluid is transported out of the human brain during sleep to clear waste, which lowers the risk of brain disorders such as Alheimer’s disease.  Getting adequate sleep should be a priority to protect brain health.

Well-being is a journey, not a quick fix


Heta Helakari, et al., Human NREM Sleep Promotes Brain-Wide Vasomotor and Respiratory Pulsations, Journal of Neuroscience, Feb. 8, 2022,

Neuroscience News, New Information about the Effects of Sleep on the Human Brain, Feb. 24, 2022,

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