Rapid eye movement, or REM, sleep is a fascinating period when most of our dreams are made. Now, in a study funded by the National Institutes of Health, a team of Japanese and U.S. researchers show that it also may be a time when the brain actively forgets. Their results suggest that forgetting during sleep may be controlled by neurons found deep inside the brain that were previously known for making an appetite stimulating hormone.

"Ever wonder why we forget many of our dreams? Our results suggest that the firing of a particular group of neurons during REM sleep controls whether the brain remembers new information after a good night's sleep," says Thomas Kilduff, director of the Center for Neuroscience at SRI International, Menlo Park, Calif., and a senior author of the study published in Science.

REM is one of several sleep stages the body cycles through every night. It first occurs about 90 minutes after falling asleep and is characterized by darting eyes, raised heart rates, paralyzed limbs, awakened brain waves, and dreaming.

For more than a century, scientists have explored the role of sleep in storing memories. While many have shown that sleep helps...

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