NPR reports that a new study from University of Rochester researchers may explain not only why we so desperately need sleep, but also the role sleep plays in preventing Alzheimer's disease.
A study of mouse brains that were asleep showed that cerebrospinal fluid flows to the brain quite rapidly while mammals are asleep, and the team speculated that the fluid is cleaning out the brain much like washing dirt off a plate. "It's like a dishwasher," said Dr. Maiken Nedergaard, one of the study's authors and a neurosurgery professor at the University of Rochester.
If the fluid performs the same function in humans that it appears to serve in mice, then human brain cells shrink when we go to sleep, making the fluid easier to circulate. When the mouse woke up, the brain cells enlarged and the fluid's flow slowed to a crawl. "It's almost like opening and closing a faucet. It's that dramatic," Dr. Nedergaard added.
The research team had previously discovered the cerebrospinal fluid was carrying away waste that gets built up in the cracks between brain cells. Those waste products are toxic to our brains, and if one fails to get a good night's sleep, leftover "brain gunk" might explain the morning sluggishness. The researchers also believe the finding explains how lack of sleep can be lethal.
This "brain cleaning process" doesn't happen all the time because, like a dishwasher, it probably requires a lot of energy. "It's probably not possible for the brain to both clean itself and at the same time [be] aware of the surroundings and talk and move and so on," Dr. Nedergaard said about how the process worked.
It should be noted that the process has not yet been directly observed in humans; even still, Nedergaard thinks that the buildup of plaque in our brains being cleaned by our spine is far from coincidence. "Isn't it interesting that Alzheimer's and all other diseases associated with dementia, they are linked to sleep disorders?" she mused.
The BBC noted several experts' comments on the study. Dr. Neil Stanley, an independent sleep expert, said of the study's implications that "There is good data on memory and learning, the psychological reason for sleep. But this is the actual physical and chemical reason for sleep, something is happening which is important."
If you want to check out a YouTube explanation of the findings directly from the study's authors, this particular video should be interesting:[Image via this History Channel documentary about the brain on YouTube]