A good night’s rest may clear your head – literally.
For centuries, scientists and philosophers have wondered why people sleep and how it affects the brain.
Only recently, for example, have scientists shown that sleep is important for storing memories.
In this new study, funded by the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health (NIH), US researchers unexpectedly found that sleep may also be the time when the brain cleanses itself of toxic molecules.
Although based on an animal model, this fascinating study published in the journal Science, showed for the first time that the space between brain cells may increase during sleep, allowing the brain to flush out toxins that build up during waking hours. These results suggest a new and important role for sleep in health and disease.
Flushing away toxins
“Sleep changes the cellular structure of the brain. It appears to be a completely different state,” said Maiken Nedergaard, MD, DMSc, co-director of the Center for Translational Neuromedicine at the University of Rochester Medical Center in New York, and a leader of the study.
Certain brain cells, called glia, control flow through the glymphatic system by shrinking or swelling. Noradrenaline is an arousing hormone that is also known to control cell volume. But when we are asleep noradrenaline levels drop, allowing certain important changes to take place.
The scientists discovered that during sleep a ‘plumbing system’ called the glymphatic system may open, letting fluid flow rapidly through the brain. The glymphatic system helps control the flow of cerebrospinal fluid (CSF), a clear liquid surrounding the brain and spinal cord.
The flush of this fluid into the brain also helps to clear away toxins, some of which are associated with Alzheimer’s disease and other neurological disorders.
To aid this flushing out, the scientists found that, when we are asleep, the space between our brain cells expands dramatically. For example, in the mice in this study, the space inside the brains increased by 60% when the mice were asleep or anesthetised.