Sometimes a restful sleep refers more to the quality of sleep than to the hours. In recent weeks there has been a lot of talk about the hours we should sleep to prevent cardiac risk or Alzheimer’s, but now research published in “Science Advances” calls attention to the quality of the user. His study concludes that not all sleep is the same when it comes to cleaning the brain.
The new research shows how the depth of sleep can affect our brain’s ability to efficiently cleanse waste and toxic proteins. The information could be an explanation for the links between aging, lack of sleep and increased risk of Alzheimer’s disease because sleep often becomes lighter and more interrupted as we age.
“Sleep is critical to the proper functioning of the brain’s cleansing system. This study shows that the deeper the sleep, the better,” says the study’s lead author, Maiken Nedergaard, of the University of Rochester.
The study shows that slow, steady heart and lung activity, associated with non-REM deep sleep, is the most optimal for the function of the glyph system — the brain’s unique process that cleans waste. The findings may also explain why some forms of anesthesia can lead to cognitive impairment in older people.
It is known that as we age it becomes more difficult to consistently achieve non-REM deep sleep.
Nedergaard and his colleagues described the glyph system in 2012. Before that, it was not understood how the brain, which maintains its own closed ecosystem, disposed of waste. The study revealed a system of pipes that collects in blood vessels and pumps cerebrospinal fluid (CSF) through brain tissue to remove waste. Further work showed that this system works mainly 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 deterioration of the glyph system by sleep disruption may be a determinant of the disease. This is in line with recent studies showing an association between sleep deprivation and an increased risk of Alzheimer’s disease.
In this work on mice, scientists used six different anesthetic regimens. While the animals were under anesthesia, they tracked brain electrical activity, cardiovascular activity and the flow of CSF cleaning through the brain.
The study raises several important clinical questions. It also strengthens the link between sleep, aging and Alzheimer’s disease. It is known that as we age it becomes more difficult to consistently achieve non-REM deep sleep, and the analysis supports the importance of deep sleep to the proper function of the glyph system.
It also demonstrates that the glyph system can be manipulated to improve sleep, a finding that may point to possible clinical approaches, such as sleep therapy or other methods to improve sleep quality, for at-risk populations.
Another valuable piece of information provided by the study is that, because several of the compounds used were analogous to anesthetics used in clinical settings, it also sheds light on the cognitive difficulties older patients often experience after surgery and suggests classes of medications that could be used to prevent this phenomenon.
“Cognitive impairment after anesthesia and surgery is a major problem,” acknowledges study co-author Tuomas Lilius, of the University of Copenhagen, Denmark. “A significant percentage of the elderly who undergo surgery experience a postoperative period of delirium or have new or worsened cognitive impairment at discharge.