Sleep helps clean our brain of toxic waste, says Maiken Nedergaard from Rochester University, New York, in a study.

Now imagine a mouse sleeping. It becomes so much easier a prey to a cat, for instance. Sleeping makes you unaware and so from an evolutionary point of view, sleep seems a bad idea. Why then do living beings still sleep? The question of why we so desperately need to sleep has been raised again and again in this column with varied answers coming from researchers who have looked at sleep in its many dimensions. One opinion recorded here earlier was that sleep repairs the damaged cells of the brain and so to avail of this service we need to sleep...when the entire brain shuts down and repair work begins. Another said sleep helps improve memory, give energy and prevents eating disorders and Alzheimer’s. It is during sleep that many ideas come, some problems may also be solved and that is because it is refreshed. While none of the above is untrue, the truth is still just a good conjecture.

Dr. Maiken Nedergaard from Rochester University, New York, has taken one definite step towards understanding sleep. She says sleep washes our brain just as a dishwasher the dishes. To understand a little bit of how our body works, the lymphatic system cleans the body, it is the biological janitor so to speak. But it is not able to reach the brain. The brain is out of its purview — despite the fact that your brain uses up about 20 percent of your body’s energy. So, how to clean the brain? Nedergaard has, elsewhere, given the example of a fish tank saying, “If you have a tank and no filter, the fish will eventually die. So, how do the brain cells get rid of their waste? Where is their filter?”

Nedergaard led a team that studied the brains of sleeping mice and noticed that during sleep, something odd was happening to the system that circulates cerebrospinal fluid through the brain and nervous system.

“It was pumping fluid into the brain and removing fluid from the brain in a very rapid pace…when mice went to sleep, their brain cells actually shrank, so it was easier for fluid to circulate. When an animal woke up, the brain cells enlarged again and the flow between cells slowed to a trickle. It’s almost like the opening and closing of a faucet. It’s that dramatic,” says Nedergaard. She has shown that the fluid was carrying away waste products that build up in the spaces between cells.

The fluid that enters the brain flows through the cells washing the toxic off them. That is why, says the researcher, we do not think very clearly if we are short of sleep…the toxic substances that are harmful to the brain have not been washed away. “It’s probably not possible for the brain to both clean itself and at the same time being aware of the surroundings and talk and move and so on…cleaning requires a lot of energy,” says Nedergaard who has come to these conclusions after her experiments on rats and baboons. But, they seem to think it must be much the same for humans too.

This understanding will contribute greatly to the cure of Alzhiemer’s. Nedergaard says, “…one of the waste products removed from the brain during sleep is beta-amyloid, the substance that forms sticky plaques associated with Alzheimer’s…Alzheimer and all other diseases associated with dementia, are linked to sleep disorders. So the patient would sleep less and less and they would not have deep sleep.”

Randall Bateman of Washington University in St. Louis was part of a team that studied how sleep affects levels of that Alzheimer’s protein, beta-amyloid. He says, “Beta-amyloid concentrations continue to increase while a person is awake. And then after people go to sleep, that concentration of beta-amyloid decreases. This report provides a beautiful mechanism by which this may be happening. It does raise the possibility that one might be able to actually control sleep in a way to improve the clearance of beta-amyloid and help prevent amyloidosis that we think can lead to Alzheimer’s disease.”

So one more argument to get into the quilt and catch up on your sleep!

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