How “Brain Washing,” Sleep, and Brain Health Go Hand in Hand

Sleep “washes the brain” and may be key to healing mild traumatic brain injury.

Posted Mar 14, 2021 |

Key Points:

  • During sleep, cerebrospinal fluid pulses through the brain, "washing out" unnecessary proteins and other brain-based "debris."
  • This waste-removal process may help the brain heal from mild traumatic injuries, a recent study suggests.
  • Among combat veterans, poor-quality sleep was associated with heightened post-concussive symptoms and impaired waste clearance in the brain. 
  • Improving sleep habits could help the brain heal faster after a concussion, the researchers speculate.

"Brainwashing" is commonly thought of as something sinister involving systematic efforts to reprogram someone's mind via Coercive Persuasion techniques. The malevolence of this type of brainwashing is captured in novels like The Manchurian Candidate. In this 1959 thriller, an American GI becomes a prisoner of war and is brainwashed. After being rescued and returning home, the story's protagonist experiences PTSD and has terrifying nightmares about his brainwashing sessions.

But washing the brain isn't always a bad thing. In recent years, the natural "brain washing" that occurs during sleep has taken on another, much more benevolent, meaning related to keeping the human brain healthy and free of debris.

Source: Yusak_P/Shutterstock

"Brain Washing" Removes Toxic Debris While We Sleep

On October 31, 2019, Boston University's research news outlet, The Brink, published an article, "Are We 'Brain Washed' During Sleep?" about a BU study (Fultz et al., 2019) that captured "the first-ever images of cerebrospinal fluid washing in and out of the brain during sleep."

In a Psychology Today blog post about this research, William Klemm wrote: "During human sleep, pulses of cerebrospinal fluid (CSF) flush throughout the brain. [...] Interestingly, the flushing seems to include most of the brain, except the brainstem and the cerebellum. These CSF waves presumably flush out unnecessary proteins and other redundant debris." Klemm also includes a link to a real-time video that shows "waves of spinal fluid washing over the brain during sleep."

Now, another study (Piantino et al., 2021) suggests that washing away the brain's toxic waste during high-quality sleep plays a vital role in healing mild traumatic brain injury (mTBI). These peer-reviewed findings were published on February 18 in the Journal of Neurotrauma.

For this study, the Oregon Health and Science University (OHSU) researchers used a proprietary MRI technique—developed by Erin Boespflug and coauthor Daniel Schwartz under the direction of Lisa Silbert—to evaluate the size of perivascular spaces (PVS) surrounding blood vessels that are part of the brain's so-called "waste clearance system."

"Imagine your brain is generating all this waste and everything is working fine. Now you get a concussion. The brain generates much more waste that it has to remove, but the system becomes plugged," first author Juan Piantino said in a March 12 news release. "We were able to very precisely measure this structure and count the number, location, and diameter of channels."

The Brain's Perivascular Waste Is Flushed Away During Sleep

According to the authors, "enlargement of these [PVS] spaces occurs in aging and is associated with the development of dementia." For their recent study in a cohort of 56 U.S. combat veterans who experienced military-blast-related mTBI in Iraq or Afghanistan, the OHSU researchers found that poor sleep quality was associated with impaired clearance of perivascular waste from the brain and persistent postconcussive symptoms.

"Impaired clearance of perivascular waste in the brain may play a critical role in morbidity after mild traumatic brain injury," the authors explain. "We aimed to determine the effect of mTBI on the burden of MRI-visible perivascular spaces in a cohort of U.S. military veterans and whether sleep modulates this effect."

Piantino et al. identified a "significant positive relationship between the number of mTBIs sustained in the military and both PVS number and volume (p=0.04)." They also found a significant interaction "between mTBI and poor sleep on PVS volume (p=0.04)" along with a correlation "between PVS number and volume, and severity of postconcussive symptoms (p=0.03)."

"This has huge implications for the armed forces as well as civilians," Piantino noted. "This study suggests sleep may play an important role in clearing waste from the brain after traumatic brain injury—and if you don't sleep very well, you might not clean your brain as efficiently."

"Improving sleep is a modifiable habit that can be improved through a variety of methods," Piantino concluded. "Longer term, we can start thinking about using this [neuroimaging] method to predict who is going to be at higher risk for cognitive problems including dementia."


Juan Piantino, Daniel L Schwartz, Madison Luther, Craig D. Newgard, Lisa Silbert, Murray Raskind, Kathleen Pagulayan, Natalia Kleinhans, Jeffrey Iliff, and Elaine Peskind. "Link Between Mild Traumatic Brain Injury, Poor Sleep, and MRI-Visible Perivascular Spaces in Veterans." Journal of Neurotrauma (First published online: February 18, 2021) DOI: 10.1089/neu.2020.7447

Nina E. Fultz, Giorgio Bonmassar, Kawin Setsompop, Robert A. Stickgold, Bruce R. Rosen, Jonathan R. Polimeni, Laura D. Lewis. "Coupled Electrophysiological, Hemodynamic, and Cerebrospinal Fluid Oscillations in Human Sleep." Science (First published; November 01, 2019) DOI: 10.1126/science.aax5440