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Rats show sleep plays crucial memory role

Almost every creature on earth needs to sleep, but why? Until recently the answer was a mystery. Scientists knew mostly what happens if there is no sleep. 

“There's data on rats that if you sleep-deprive rats for the order of about three weeks, they'll die,” says Dr. Allen Pack, who heads the University of Pennsylvania Sleep Center.

Lots of research shows that humans who don't sleep enough suffer more heart disease, disorientation and other problems.

But it is experiments with healthy rats, getting plenty of rest, which are providing a key new concept about sleep.

The concept holds that sleep is most crucial for memory. Not just remembering things, but gaining insight and understanding.

In their lab at the Massachusetts Institute of Technology, Dr. Matt Wilson and his team monitor the electrical signals from thousands of individual nerve cells inside the brains of rats. When a rat performs a task like going through a maze, the scientists see a specific pattern. When the rat sleeps, its brain repeats the pattern.

“We can see that they are revisiting, re-expressing, replaying past memory,” says Wilson.

In this case, the rat's brain is just like a human's — working hard while the body sleeps — to process everything that happened during wakefulness.

“To put together things that may not have actually occurred together, to try to learn from that,” says Wilson. “[The brain is trying to] identify new relationships, to learn new things from old memory.”

Dr. Wilson says this is why we so often understand things much more clearly after a good night's rest.

“The idea that you could learn something new, or gain some novel insight, as a consequence of sleeping on it, is, what we think of, actually, as a primary function of sleep,” he says.

In other words, sleep is not just to refresh, but a critical time for both memory and learning.

Wednesday on NBC Nightly News: The business of sleep: Are we paying too high a price for a good night's rest?