Sleep on It for Long-Term Memory

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Scripps Howard News Service
You may need to "sleep on it'' to effectively learn something, a new study by Harvard Medical School researchers suggests.

The research, published Wednesday in the journal Nature Neuroscience, adds to the evidence that sleep is needed for learning, while denying sleep the night after learning a new task seems to muddle memory consolidation.

The study found that no amount of sleep on the following two nights can make up for the toll of an initial all-nighter.

"You need sleep that first night if you want to improve on a task,'' said Robert Stickgold, an assistant professor of psychiatry at Massachusetts Mental Health Center and lead author of the study.

Sleep is important for maintaining attention and alertness when we're trying to learn. But scientists at Harvard and elsewhere have found that the process of turning information from a short-term to a long-term, useful memory seems to require getting a good night's sleep.

Specifically, brain imaging tests and other experiments point to a chemical released during dreaming that passes messages between brain cells and seems to consolidate memory.

The "rapid-eye-movement'' sleep that sets us up to dream comes in short spurts within deeper sleep several times each night. Only about 25 percent of sleep is REM sleep.

In an earlier experiment, Stickgold and colleagues had found that people who learned a particular task did not improve their performance when tested later the same day, but did do better remembering it after a night of sleep.

To find out if the night's sleep really caused the improvement, Stickgold trained 24 subjects in the same visual discrimination task _ identifying the orientation of three diagonal bars flashed for one-sixtieth of a second on the lower left quadrant of a computer screen full of horizontal stripes.

Half of the subjects went to sleep that night while the other half were kept awake until the second night of the study. Both groups were allowed to sleep on the second and third nights.

On day four, both groups were tested on the visual discrimination task. Those who slept the first night identified the correct orientation of the diagonal bars much more rapidly than they had the first day. The other group showed no improvement, despite the two nights of catch-up sleep.

"We think that getting that first night's sleep starts the process of memory consolidation,'' Stickgold said. "It seems that memories normally wash out of the brain unless some process nails them down. My suspicion is that sleep is one of those things that does the nailing down.''

Scientists also have evidence that sleep isn't necessarily the only way that memories get set in the brain.

Dr. William Dement, a noted sleep researcher who teaches at Stanford University, says "REM may be one factor that helps memories stick but it is not absolutely required." He cites other studies that have found sleep did not affect the retention of information. In his book, "The Promise of Sleep,'' Dement notes the case of an Israeli war veteran who suffered a wound at the base of his brain that wiped out his ability to have REM sleep or to dream, yet did not hinder his ability to learn new skills or remember. "So whether REM sleep helps us learn and remember has not been proven conclusively," Dement said. "But I think the combination of anecdotal and scientific evidence is very suggestive that the time-honored tradition of cramming late into the night for an overdue assignment can be disastrous."

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