Depth of sleep impacts the brain’s ability to flush out toxins
New research from the University of Rochester Medical Center (URMC) shows that our depth of sleep affects the brain’s process of washing away toxic proteins and waste. And because our sleep becomes lighter as we age, researchers believe their findings, published February 27th in Science Advances, could potentially unlock the mystery of aging and sleep deprivation in relation to heightened risk of Alzheimer’s disease.
“Sleep is critical to the function of the brain’s waste removal system and this study shows that the deeper the sleep the better,” said lead author Maiken Nedergaard, M.D., D.M.Sc., co-director of the Center for Translational Neuromedicine at URMC. “These findings also add to the increasingly clear evidence that quality of sleep or sleep deprivation can predict the onset of Alzheimer’s and dementia.”
The study shows that deep non-REM sleep, during which both the brain and cardiopulmonary activity slow down, is the perfect sleep stage for the glymphatic system to function properly. The glymphatic system, a “plumbing” system that pumps cerebral spinal fluid (CSF) through brain tissue to flush away waste, was only just discovered by Nedergaard and her team in 2012.
Toxic proteins that accumulate in the brain, such as beta amyloid and tau, are associated with the development of Alzheimer’s. Therefore, researchers believe that an impairment of the glymphatic system due to weakened sleep may encourage the development disease.
Nedergaard and her team used anesthetized mice to conduct their experiment. While under six different anesthetic regimens, researchers watched the mice’s brain electrical activity, cardiovascular activity, and the flow of CSF through the brain. They found that the drugs ketamine and xylazine (K/X) replicated the deep non-REM sleep needed for proper cleansing.
“The synchronized waves of neural activity during deep slow-wave sleep, specifically firing patterns that move from front of the brain to the back, coincide with what we know about the flow of CSF in the glymphatic system,” said first author Lauren Hablitz, Ph.D., a postdoctoral associate in Nedergaard’s lab. “It appears that the chemicals involved in the firing of neurons, namely ions, drive a process of osmosis which helps pull the fluid through brain tissue.”
Via this experiment, researchers found that sleep can be enhanced to better the function of the glymphatic system. Later down the road, this could prove to be a form of therapy for patients at risk for developing Alzheimer’s or dementia. And researchers also noted that certain anesthetics used in clinical settings can lead to cognitive difficulties, which could also affect glymphatic activity.
“Cognitive impairment after anesthesia and surgery is a major problem,” said co-author Tuomas Lilius, M.D., Ph.D., with the Center for Translational Neuromedicine at the University of Copenhagen. “A significant percentage of elderly patients that undergo surgery experience a postoperative period of delirium or have a new or worsened cognitive impairment at discharge.”