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Monday, Dec 1, 2008
New research suggests that people learn while they sleep.
Jul 19, 2000 | We interrupt the centennial celebration for "The Interpretation of Dreams," Freud's seminal work and the founding document of psychoanalysis, to bring you a special bulletin. Dreams are not, after all, depraved desires in disguise. We now have direct human evidence that what dreams are really about is something entirely respectable: learning.
Neuroscientists at several institutions in Belgium and Canada report that patterns of brain activity in people as they learn a task are replayed while they sleep. It's the first visual explanation for why both animals and people learn better if they sleep on it. The research, published in the August issue of the journal Nature Neuroscience, appears to demonstrate the reason that people perform better on a test if they study the day before, instead of cramming at the last minute. Their brains are efficiently using sleep time to practice, practice, practice.
"It's the first to show that a particular part of the brain involved in learning is active after you learn," says Sean P.A. Drummond, a psychiatry professor at the University of California at San Diego, who has used brain imaging to study how sleep deprivation impairs people's ability to learn.
Using the brain imaging method called positron emission tomography, or PET scanning, scientists observed the brains of study subjects as they slept after learning what neuropsychologists call a "reaction task." (They pressed buttons in response to symbols flashed at them.) There are several studies showing that both lab animals and people get better at this kind of thing after a night's sleep. These subjects did too.
But the PET scans went on to show, for the first time, that their brain activity patterns during sleep were quite similar to the patterns generated when they were awake and learning the button-pressing routine. The scientists concluded that the sleeping brain was probably stabilizing and strengthening memories of the task via something like a series of instant replays. In a word, it was practicing.
These brain patterns manifested themselves only during that stage of sleep known as REM (for rapid eye movement, because your eyes dart madly around beneath your lids at this sleep stage). REM sleep happens four or five times a night, and folklore has it that dream time is REM time. The truth is that dreaming goes on all night, at every sleep stage. But REM sleep dreams do tend to be our most vivid and memorable, and are probably more frequent than other dreams.
"We can see exactly where this extra activity is, and it happens only during REM sleep," says one of the study's authors, Carlyle Smith, a psychology professor at Trent University in Peterborough, Ontario. "These people show great improvement when you test them the next day. What else could that extra neuronal activity during REM sleep be about? It's only in the group that learns, exactly what you'd predict you would see."
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