At night, our cells may clean our brain

Process may reduce risk of Alzheimer’s

Studies in mice indicate that our brains may go through a process while we sleep that rids them of toxins that build up during the day

Did you ever wonder what happens to our brains at night? If recent studies in mice are any indication, our brains may go through a process that rids them of toxins that build up during the day.

The studies suggest that during sleep, there is an expansion of extracellular space within the brain that corresponds with increased fluid movement around and into the deep parts of the brain. This fluid movement is associated with a more robust exchange of small compounds into and out of the brain itself.

In mice studies, some of these compounds include toxic proteins—namely amyloid beta protein, which is implicated in the development of Alzheimer’s disease and other dementias. How external fluid moves into, within and out of the brain tissue still remains a mystery. 

The brain cleaning process

A group of scientists who have conducted several recent experiments on this system in mice have begun using the term “glymphatic system” to characterize this process.

The “G” in “glymphatic” stands for “glial”—which are a broad class of cells that support the health of neurons in the brain and may form the passageways through which this fluid moves.

The “lymphatic” part of “glymphatic” refers to the human lymphatic system, which is series of passageways—distinct from conventional blood vessels—charged with trafficking and clearance of certain immune compounds in the body.

The human brain

While all the studies to date have been in mice or other animal models, there are numerous studies in humans that link poor quality of sleep with the long-term future risk of developing Alzheimer’s disease. The small but growing body of literature describing the glymphatic system in mice has made many people wonder if this concept is the mechanistic link that explains why poor quality of sleep can give rise to Alzheimer’s disease.

Our research

We are conducting a pilot study supported by the Michigan Alzheimer’s Disease Center to determine if we can use new MRI methods to characterize this fluid movement in healthy adults and those with mild cognitive symptoms. If our hypotheses are correct, we hope that this study will provide the first evidence supporting the existence of the glymphatic system in humans.

Public health implications

Even though this system is currently not well understood, it could have enormous public health implications.

If this same system of fluid movement and toxic brain protein clearance is found to exist in humans, finding ways to augment this natural system will move the forefront of potential new treatments for dementias.

In the same light, improving quality of sleep at night would take on much greater clinical significance for anyone at risk for dementias if we were clear on exactly how and why poor quality of sleep leads to progressive cognitive decline.

Take the next steps

Vikas KotagalVikas Kotagal, M.D., M.S., assistant professor of neurology in the University of Michigan Department of Neurology, sees outpatients with movement disorders including Parkinson’s disease, atypical Parkinsonian conditions, tremor and gait impairments. He directs a subspecialty clinic for patients with suspected normal pressure hydrocephalus. He is passionate about issues impacting access to care for patients with neurodegenerative conditions.



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