October 18, 2013

Why humans (and most other creatures) sleep

This is big news. It answers two longstanding questions about the brain.

The short version is that when we sleep, our brains flush out the garbage that accumulates while we're awake. And that garbage is, in large part, amyloid-beta, the stuff that causes Alzheimer's disease and other neurodegenerative diseases. As I say, this is big news.

Apparently the brain flushes out the garbage ten times faster when we're asleep than when we're awake. And, wildly, the brain's cells literally shrink while we sleep -- so the "cleaning fluid" sent from the spine can flush the area clean! It's kind of like putting the restaurant chairs up on the table so you can wash the floor. Here's that section from the article:
Another startling finding was that the cells in the brain "shrink" by 60 percent during sleep. This contraction creates more space between the cells and allows CSF to wash more freely through the brain tissue. In contrast, when awake the brain's cells are closer together, restricting the flow of CSF.
This answers the big question: why do we sleep? It was an issue that caused consternation among scientists because when we're asleep, we're vulnerable to predators. That didn't make sense in evolutionary terms. The question was always: what possible benefit of sleep could outweigh the danger of leaving oneself vulnerable to attack (and death). Now we have the answer.

Another question that arose in recent years is -- why is the brain as active while we sleep as when we're awake? What could possibly be going on in there? Well, now we know: the brain is busy cleaning up after an active day of thinking.

Fascinating stuff. I love that science finally figured this out. We must sleep so our brains can work properly. But to me, this news begs a question.

Do older people get Alzheimer's at higher rates than young people because they sleep so little? We're always hearing that older people have trouble sleeping. I was surprised they didn't mention this in the article. I'll keep my eye out for an answer and will report back if I find it.


cm said...

They say old people need less sleep. I can't remember why. I guess I'm old.

Artichoke Annie said...

No, no, no old people need lots of sleep, like little babies. Take it from me a registered old person.