Unlocking the Mysteries of Sleep

Medically Reviewed by Gary D. Vogin, MD
From the WebMD Archives

Nov. 1, 2001 -- "I'll sleep on it" may seem like a last resort when problems get too murky. But new science is revealing why this time-tested remedy works. Researchers are also learning more about the role that sleep plays -- or doesn't play -- in helping us cram for tests or learn new skills like dancing, tennis, and the piano.

The studies appear in the current issue of the journal Science.

Researchers have long debated the connection between REM (rapid eye movement) sleep and learning. A popular notion has been that sleeping allows the brain to consolidate memories, to facilitate learning. But one group of researchers finds just the opposite, that sleep plays little role in helping us learn new material.

"Learning occurs during alert, waking hours, not during sleep," says Jerome M. Siegel, PhD, professor of psychiatry at UCLA and chief of neurobiology research at Sepulveda VA Medical Center in Los Angeles.

If anything, getting a good night's sleep helps with concentration -- that's the benefit, Siegel tells WebMD. "It's very important to be well-rested if you want to learn something. You don't want to fall asleep in the test. It's like eating before a test; you have to take care of yourself. It's not that REM sleep helps learning. It's not important for memory."

In his paper, Siegel reviewed numerous animal and human studies, looking at the effects of REM sleep. Many found that depriving animals and humans of REM sleep did not impair their ability to form long-term memories.

"The switch from temporary memory to permanent memory seems to occur during waking hours," he says. "You don't need sleep to retain it."

There are plenty of people who have no REM sleep -- for various reasons -- who don't have memory problems, Siegel says. People taking drugs known as MAO inhibitors for depression are a perfect example; so are some brain injury patients.

Also, people who learn very well -- those with high IQs -- do not seem to have any pattern of greater REM sleep than those who are retarded. Likewise, some of the smartest animals -- dolphins, whales -- get very little REM sleep whereas the platypus, an entirely instinct-driven animal, gets more REM sleep than any other animal.

In fact, among all the animals, humans don't have especially high or low amounts of REM sleep, he tells WebMD. "We really don't know the purpose of REM sleep," Siegel says. "We don't even fully understand learning."

REM sleep may actually help us with certain types of learning -- what's called "procedural" learning, "when you're learning how rather than what," says Robert Stickgold, PhD, assistant professor of psychiatry at Harvard Medical School and a cognitive neuroscientist.

Stickgold agrees with Siegel, that "simple declarative memory" -- like remembering facts for a test, phone numbers, or word lists -- is not dependent on sleep. "Everything we learn while waking gets learned before we sleep. So clearly those are not dependent on sleep for their initial consolidation," he tells WebMD.

Studies of procedural learning, however, "show clear evidence that you don't get improvement until you sleep," Siegel says.

A perfect example: studies show that when learning muscle-related tasks -- like dancing, piano playing, gymnastics -- there is significant improvement after a night's sleep, he tells WebMD.

This type of learning occurs in the cortex of the brain, Siegel explains. "The hippocampus hands out the 'episodic details' like phone numbers, what you had for breakfast this morning." The facts you crammed for today's test are likely delivered via the hippocampus.

But it's the neocortex that's working when you need to re-process information, as in learning muscle-related tasks. It's also the neocortex that will provide the answer when someone asks what you would like for breakfast, he says.

"Your neocortex would process all the information -- the fact that you prefer waffles, but the last couple of times you had them they were kinda soggy," Stickgold tells WebMD.

It's also your neocortex that makes "sleeping on a problem" -- a concept that seems known across all cultures -- so effective, he says. "You're offered the perfect job, but it's not in an ideal city. You can't decide which college is right for you. Everybody knows that you can count on the fact that if you go to bed confused, when you wake up, you'll have the answer, or the answer isn't to be found."

"I think the mysteries of sleep, of REM sleep, are yielding," says David Dinges, PhD, a sleep researcher, professor of psychology and psychiatry at the University of Pennsylvania School of Medicine.

Dinges is currently president of the Sleep Research Society, and agreed to comment on the studies for WebMD.

"As the technology gets better, our ability to penetrate the brain gets better, allowing these and other scientists to push the envelope in our understanding," Dinges tells WebMD. These are small pieces of evidence in a giant, endless puzzle."

Sleep is known to be important to cognitive function, he says. "We know that if you are sleep-deprived, it's tougher to remember, harder to think quickly, more difficult to think of new solutions. The debate among scientists is whether those are completely different functions, or are they related? Does REM sleep restabilize us from a cognitive and emotional perspective or is it necessary so that our brains can lay down memories?"

Likely so, says Dinges. "I'd be surprised if there was not some fundamental role of sleep in facilitating learning and memory, but how specific we can be remains to be debated. It's partly tied up with how we define memory and learning -- which may not be exactly how nature separates it out."