Our Brain-Scrubbing System

Rub-a-dub-dub, three men in a tub; and who do you think they be? – Nursery Rhyme


We have known for quite some time that too little sleep can really deplete your brain’s energy, but scientists have really never understood why.  That is until a recently published study conducted by Dr. Maiken Nedergaard, director of the Center for Translational Neuromedicine at the University of Rochester Medical Center.  This new study clearly intimates that a solid night of sleep leaves you feeling refreshed and awake because of an until now unknown system that “scrubs” away brain cell waste products, and is most highly active when we are asleep.  According to Dr. Nedergaard, “We have a cleaning system that almost stops when we are awake and starts when we sleep. It’s almost like opening and closing a faucet — it’s that dramatic.”  It works like neuronal trash removal, cleaning up the toxic by-products in the brain which build up during the day when we are awake.

This “brain-scrubbing” system, known as the glymphatic system, is a metabolic waste clearance system of the central nervous system (CNS).  The CNS is comprised of the brain and spinal cord.  The lymphatic system is responsible for the removal of metabolic waste products and excess fluid from the rest of the tissues of the body.  Our CNS has no such lymphatic vessels.  The term “glymphatic system” was actually coined by Dr. Nedergaard based on the fact that the system is dependent upon specialized CNS cells known as glial cells, and the fact that it acts in similar function to the body’s lymphatic system.  It is a highly organized system which is made up of a series of vessels that run intimately alongside the brain’s blood vessels.

Such a finding will likely not only significantly change our basic understanding of sleep, but may actually lead to new and effective treatment interventions for such neurodegenerative brain disorders as Alzheimer’s, Lewy Body dementia, Parkinson’s, and others which are believed to be associated with the accumulation of toxic brain metabolic byproducts and an abnormal buildup of certain toxic proteins. According to Dr. Nedergarrd, “Waste clearance is of central importance to every organ, and there have been long-standing questions about how the brain gets rid of its waste.  This work shows that the brain is cleansing itself in a more organized way and on a much larger scale than has been realized previously.”

Scientists have known for quite some time that cerebrospinal fluid (CSF), a clear and colorless fluid which bathes and protects the brain and spinal cord, plays a vital role in carrying nutrients to the brain tissue and carrying away metabolic waste byproducts from brain tissue through a rather slow and tedious process known as diffusion.  Diffusion is the passive movement of any substance from a higher concentration to an area of lower concentration of that substance.  This newly identified glymphatic system actually facilitates circulation of the CSF throughout the brain in a much more efficient manner known as convection.  Via convection the glymphatic system actually moves much greater volumes of CSF through the brain under pressure.  The CSF is “pumped” into the brain along the glymphatic channels that shadow the arteries of the brain, and then bathes the brain tissue collecting the metabolic toxins, before finally accumulating in glymphatic channels around the veins of the brain, ultimately being drained away.

Although for decades scientists had hypothesized the presence of a system in the brain providing for far greater CSF movement than was known to exist, it was not until just recently that the technology was actually available to visualize it.  This is due to the fact that the glymphatic system is only operable when intact and in living animals.  For many years only pieces of the brain of deceased animals, and only sections of the brain, were able to be studied.   As Dr. Nedergaard put it, “It’s a hydraulic system.  Once you open it, you break the connections, and it cannot be studied.”  That is, not until the recent technological development of the two-photon microscope.

Dr. Nedergaard’s study shows that “the brain has different functional states when asleep and when awake.  In fact, the restorative nature of sleep appears to be the result of the active clearance of the by-products of neural activity that accumulate during wakefulness.  Her research team found that the glymphatic system was some ten times more active during sleep than when awake.  She notes that “The brain has only limited energy at its disposal and it appears that it must choose between two different functional states — awake and aware or asleep and cleaning up.”

Her team further identified that more than 50% of the protein, amyloid beta (which is known to accumulate in the brain of Alzheimer’s patients), found in the brains of lab mice, which are astonishingly similar to human brains, was actually removed via the glymphatic system.  According to one of Dr. Nedergaard’s research assistant professors, Jeffrey Iliff, Ph.D., “Understanding how the brain copes with waste is critical. In every organ, waste clearance is as basic an issue as how nutrients are delivered. In the brain, it’s an especially interesting subject, because in essentially all neurodegenerative diseases, including Alzheimer’s disease, protein waste accumulates and eventually suffocates and kills the neuronal network of the brain…If the glymphatic system fails to cleanse the brain as it is meant to, either as a consequence of normal aging, or in response to brain injury, waste may begin to accumulate in the brain. This may be what is happening with amyloid deposits in Alzheimer’s disease.  Perhaps increasing the activity of the glymphatic system might help prevent amyloid deposition from building up or could offer a new way to clean out buildups of the material in established Alzheimer’s disease.”

While researchers remain uncertain if the build-up of amyloid beta proteins in the brain are the cause, or a result, of a variety of neurodegenerative diseases, Dr. Nedergaard’s team’s discovery cannot help but further our understanding of how sleep clears waste byproducts from the human brain, and thus lead to new and innovative treatment approaches.




Glenn E. Miller, M.D. is a Board Certified Psychiatrist.  Educated as a pharmacist, physician and psychiatrist Dr. Miller has been in private practice in Santa Barbara for more than twenty-five years.  Dr. Miller is co-author of Ancient Herbs, Modern Medicine: Improving Your Health by Combining Chinese Herbal Medicine and Western Medicine.  Opinions in the column are Dr. Miller’s and not necessarily those of this newspaper.  Send questions or topics you would like covered to glenn@healthymindhealthyfuture.com