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Sleep Replenishes the Memory Bank

Studies find a good night's shut-eye revives verbal, motor skills

WEDNESDAY, Oct. 8, 2003 (HealthDayNews) -- If you want to improve your recall, try getting more shut-eye at night.

Two studies appearing in the Oct. 9 issue of Nature found human memory improves after sleeping.

Each study looked at memory for different tasks -- one tested participants on motor skills and the other on speech memory -- but participants performed better after sleeping in both studies.

"A full night of sleep is critical to enhancing learning," says an author of one of the studies, Matthew Walker, an instructor of psychiatry at Harvard Medical School in Boston. "It's almost as though at night an editor comes in while you're sleeping and reorganizes and enhances your memories to prepare them for the next day."

The author of the second study, Daniel Margoliash, a professor of psychology and organismal biology at the University of Chicago, says two things happen during sleep. The first is that the brain recovers parts of memories that have been lost during the day. The second is that memories are stabilized for long-term storage while you slumber.

For their study, Walker and his colleagues enlisted the help of 100 healthy young adults and split them into eight different groups. All of the groups learned specific finger-tapping sequences. The only thing that varied from group to group was the point in the sleep-wake cycle in which they learned the task.

Walker says the researchers discovered three distinct stages that occur when humans create memories. During the first stage, Walker says it's as if the human mind creates a "Word" file on the computer. The information is there, but could be easily lost until you've hit the save button. Hitting the save button takes only seconds on a computer, but Walker says it can take up to six hours in a person. During this time, the memory becomes more stable, and is less likely to be forgotten.

The second stage of memory processing occurs during sleep, according to Walker, and he says the last two hours of sleep in an eight-hour night are the most critical for memory storage. He says during this stage the file is reopened and then reorganized. This stage, he says, enhances the memory and prepares it for recall.

The last stage of memory occurs when you recall a memory. Walker says it's as if you've reopened the file and can modify its content. Slight changes to the memory may then be saved. This information could be particularly useful when treating people with problems such as post-traumatic stress disorder. Walker says that as a memory is brought up in therapy, it could be altered slightly, making it a little bit less traumatic each time.

In the second study, Margoliash and his colleagues, Howard Nusbaum and Kimberly Fenn, had 48 volunteers listen to simple words on a speech synthesizer, and then asked them to identify the sounds. Twelve participants were tested in the morning and then re-tested 12 hours later in the day. Another 12 volunteers were tested in the evening and then again 12 hours later, but this group had the chance to sleep before being retested. The final group of 24 acted as a control group and were retested immediately after the first test.

The researchers found performance was better for the participants who were tested and then had a chance to sleep. Those who received testing in the morning and then again 12 hours later, lost about half of what they had learned during the intervening hours, Margoliash says.

"However, if you trained in the morning and then were tested again in the following morning, you'll have regained during sleep what you lost during the previous day," he says.

Margoliash says the most important thing to remember is that "Mom was right. Get a good night's sleep."

More information

For tips on getting a good night's sleep, visit the National Sleep Foundation or the New York University School of Medicine's Sleep Disorders Center.

SOURCES: Daniel Margoliash, Ph.D., professor, psychology and organismal biology, University of Chicago; Matthew Walker, Ph.D., instructor, psychiatry, Harvard Medical School, Boston; Oct. 9, 2003, Nature
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