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Brain Uses Dreams to Process Memories

Brain Uses Dreams to Process Memories

November 1, 2000 By Merritt McKinney

NEW YORK (Reuters Health) - The dreams we have at night often seem full of nonsense, but for the brain, sleep is the time for making sense of much of the information it takes in during waking hours, researchers say.

In fact, sleep is essential for "learning" certain types of memories, according to one of the authors of a new report on dreams published in the November 2nd issue of the journal Scie

"The brain is actually quite active during sleep," Dr. Robert Stickgold of Harvard Medical School in Boston, Massachusetts, told Reuters Health in an interview. Sleep is "not a time when we turn off the brain and let it rest," he said.

During the day, the brain takes in information at a much faster clip than it can process it, Stickgold explained. The brain seems to perform some of this processing during sleep, he added.

In the Science article, Stickgold and colleagues review existing research on sleep, learning, dreams and memory processing.

For years there was a dearth of serious science on dreams, according to Stickgold. Recently, however, scientists have been able to begin studying the relationship between dreams and various brain activities.

"We now can really start doing experimental science on dreams," Stickgold said.

The Harvard researcher noted that most cultures have an expression for "sleeping on it"--waiting to make a decision until after a good night's sleep.

For simple learning or memory tasks, "sleeping on it" is not necessary. For example, if asked to remember a phone number, a person does not need to sleep on it, Stickgold noted.

But the REM, or rapid eye movement, phase of sleep seems to be critical for what is known as procedural learning, Stickgold said. He explained that this type of learning involves learning how to do things, such as playing the piano. It also is involved in making decisions.

For instance, if a person is offered a dream job, but taking the job means he or she has to move across the country to an unfamiliar place, then it may be a good idea to sleep on the idea, according to Stickgold.

Or a pianist might be having trouble with a particular piece one afternoon but can play the tune perfectly the next morning after a good night's sleep, the researcher explained.

"You have all the facts you need," Stickgold said, but the information "just has to get sorted out." During sleep, particularly the REM phase, the brain is able to take facts and integrate them, he added.

"That seems to happen very smoothly at night," he said.

"As other people have noted, it's very clear that sleep is not necessary for all memory processing," Stickgold said. "But there are certain areas for which it is clearly necessary."

Besides procedural learning, research has suggested that REM sleep is needed to "complete the wiring" of the visual system, Stickgold added.

Sleep may be involved in "strengthening and integrating and maybe, in some cases, erasing memories from the immediate and distant past," he said. "Dreaming is probably a piece of this process."

SOURCE: Science 2001;294:1052-1057.

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