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Patrick Guilfoile: Who needs sleep?

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A rare genetic form of insomnia eventually causes affected individuals to die due to lack of sleep. Many consider intentional sleep deprivation to be a form of torture. Numerous studies have documented impairment in mental abilities in individuals who don’t get enough sleep. Yet, in spite of how clearly important sleep is, we haven’t understood why it is necessary.

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Researchers from the University of Rochester have provided at least a partial answer to why we (or at least mice) sleep. They built on their recent work showing that the brain is full of microscopic, fluid-filled channels, which can carry toxins away from nerve cells. In their most recent study, these scientists studied the function of these channels in sleeping and awake mice.

One of the researchers spent two years training mice to fall asleep on a specialized kind of microscope. (And you think your day job is tedious!)  

Once the mice were sleeping on the microscope, the researchers injected a green dye into their brains.

The microscope allowed them to trace how quickly the dye traveled through the mouse’s brain while it was sleeping.

The scientists then woke up the mice and then injected a red dye into their brains.

The scientists separately tracked, using the microscope, how quickly the red dye moved through the brains of now-awake mice.

They found that the dye moved much more rapidly when the mice were asleep. In fact, they found that the channels in the brain were much wider in sleeping mice, as compared to awake mice. The fluid flow was therefore much faster (about 20 times faster) in the sleeping mice, suggesting that sleep allowed toxic products of metabolism to more rapidly flush out of the brain when the mice were asleep.

The researchers also injected molecules that contribute to Alzheimer’s disease into the brains of mice, and these also flushed out of the system much more quickly during sleep.

This research suggests that insomnia may actually contribute to Alzheimers and similar diseases, by allowing harmful products to accumulate and damage cells.  

Like most research, this study raises more questions than it answers. For example, do other animals have the same channels in their brain, and do they open during sleep, allowing harmful materials to be flushed out?  Does the accumulation of these toxins cause us to become sleepy?

Assuming this research applies to humans, it is intriguing to think that we may literally undergo a brain washing each time we sleep.

And, just as stopping a dishwasher before the cycle is complete may allow gunk to accumulate on our dishes, a lack of sleep may cause the accumulation of toxins that might ultimately gunk up our brains.

More information is available in:  “Sleep drives metabolite clearance from the adult brain” Lulu Xie and others, Science 342: 373-376, Oct. 13, 2013.

PATRICK GUILFOILE has a Ph.D. in bacteriology and is the associate vice president at Bemidji State University.

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