In a new study, researchers found how the depth of sleep can impact the brain’s ability to efficiently wash away waste and toxic proteins.
Because sleep often becomes increasingly lighter and more disrupted as people become older, the study reinforces and potentially explains the links between aging, sleep deprivation, and heightened risk for Alzheimer’s disease.
The research was conducted by a team at the University of Rochester Medical Center and elsewhere.
Sleep is critical to the function of the brain’s waste removal system and this study shows that the deeper the sleep the better.
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 indicates that the slow and steady brain and cardiopulmonary activity associated with deep non-REM sleep are optimal for the function of the glymphatic system, the brain’s unique process of removing waste.
The findings may also explain why some forms of anesthesia can lead to cognitive impairment in older adults.
The previously unknown glymphatic system was first described by Nedergaard and her colleagues in 2012.
Prior to that point, scientists did not fully understand how the brain, which maintains its own closed ecosystem, removed waste.
The study revealed a system of plumbing which piggybacks on blood vessels and pumps cerebral spinal fluid (CSF) through brain tissue to wash away waste.
A subsequent study showed that this system primarily works while we sleep.
Because the accumulation of toxic proteins such as beta-amyloid and tau in the brain are associated with Alzheimer’s disease, researchers have speculated that impairment of the glymphatic system due to disrupted sleep could be a driver of the disease.
This squares with clinical observations that show an association between sleep deprivation and heightened risk for Alzheimer’s.
In the current study, the researchers conducted experiments with mice that were anesthetized with six different anesthetic regimens.
While the animals were under anesthesia, the researchers tracked brain electrical activity, cardiovascular activity, and the cleansing flow of CSF through the brain.
The team observed that a combination of the drugs ketamine and xylazine (K/X) most closely replicated the slow and steady electrical activity in the brain and slow heart rate associated with deep non-REM sleep.
Furthermore, the electrical activity in the brains of mice administered K/X appeared to be optimal for the function of the glymphatic system.
The team says 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.”
The study reinforces the importance of deep sleep to the proper function of the glymphatic system.
It also demonstrates that the glymphatic system can be manipulated by enhancing sleep, such as sleep therapy or other methods to boost the quality of sleep, for at-risk populations.
The lead author of the study is Maiken Nedergaard, M.D., D.M.Sc.
The study is published in the journal Science Advances.
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