During sleep, the “slow wave” activity of nerve cells makes room for cerebral spinal fluid to move in and out of the brain. It is this process that is now believed to rinse out metabolic waste products. These products include beta-amyloid, which is a protein that has been found in the brain of those suffering from dementia.
The study that was reported in the journal Science does stress that the findings do not prove that deep sleep helps to ward off dementia or other diseases. It does help researchers understand why poor sleep quality is linked to higher risks of various chronic conditions, from memory issues such as dementia and depression to heart disease.
Previous studies have shown that cerebral spinal fluid, or CSF, can help to clear metabolic byproducts from the brain. It has also been shown that this process appears to speed up during sleep, but the “how’s” and “why’s” still remain to be studied. This is why Laura Lewis, an assistant professor of biomedical engineering at Boston University, set out to find the answers by recruiting 11 healthy adults for a sleep study.
The study used noninvasive techniques, including advanced MRI, to monitor fluid flow in the brain, and electroencephalograms to gauge electrical activity in brain cells. Lewis and her team found that housecleaning may be one of the fundamental things that the brain takes care of during sleep. When participants were in a deep sleep, each pulse in slow-wave brain activity was followed by oscillations in blood flow and volume, which allowed CSF to flow into fluid-filled cavities in the central brain.
Large Pulsing Waves
CSF moved in large “pulsing waves” that were seen only during deep sleep, Lewis explained. Experts agree that it is reasonable to conclude that slow-wave sleep promotes the flushing of waste from the brain.
This study helps to explain how and why sleep is important for keeping neurons healthy, facilitating the removal of toxic molecules.
Another sleep medicine specialist who was not involved in the study agreed. “There is growing evidence, with this study and others, that sleep plays a role in clearing toxins from the brain,” said Dr. Raman Malhotra, an associate professor of neurology at Washington University in St. Louis.
Other research has concluded that sleep loss can promote the buildup of unwanted proteins in the brain. For instance, a recent government study found that one night of sleep deprivation can trigger an increase in beta-amyloid in the brains of healthy adults.
This study adds to the mounting evidence about the role of sleep and brain health, and the research shows how individuals who don’t get enough can suffer from chronic health conditions. To help avoid health issues, health care professionals suggest getting 7 to 9 hours a night.