To sleep… perchance to learn

To Sleep, Perchance to Learn: Neural Links to Memory

November 3, 1992

To learn a complex skill like typing, driving a car or scuba diving most effectively, scientists offer this advice to students of all ages:

Go to bed and dream about it.

The newest study demonstrating a link between dreams and memory was presented here last week at the annual meeting of the Society for Neuroscience.

Dr. Avi Karni, a neuroscientist at the Weizmann Institute of Science in Rehovot, Israel, reported that people show better performance on a test of visual memory after a night's sleep. People taught the task late in the day did not show improvement until the next day, Dr. Karni said, "so we wondered if there is a stage of sleep that is important for memory consolidation." And so volunteers entered a sleep laboratory and were woken up at various times of night.

When slow wave sleep was disrupted, the kind experienced through most of the night, people always showed improvement the next day, Dr. Karni said. But when rapid eye movement, or REM sleep, the kind experienced during dreams, was disrupted, he said, people stayed at the previous day's threshold.

"This means that REM periods are windows of time in sleep that allow us to work on memory," Dr. Karni said. "REM sleep may be an important mechanism to make sure you don't lose information learned over the latter part of the day, especially for 'how to' or procedural memory."

Dr. Larry Squire, a leading authority on memory at the University of California at San Diego Veterans Administration Hospital, said the role of memory and sleep was still somewhat speculative. "It's hard to rule out nonspecific effects of sleep and dream deprivation," he said. "Lack of sleep may lead to a general decline in cognitive performance and not just memory."

But Dr. Carlyle Smith, a Canadian psychologist at Trent University in Peterborough, Ontario, said his research on rats and college students pointed to a strong link between dreaming and memory.

Rats were put in a milky bath with a hidden platform, he said. They swam around, using spatial clues from surroundings, to find the platform. The next day, he said, they quickly found the platform. But when the rats were deprived of REM sleep, they were slower in finding the platform the next day.

In human experiments, Dr. Smith found that performance on a task requiring memory of complex rules deteriorates by 20 percent to 30 percent if people do not sleep the night after learning the rules.

"But you don't have to stay up all night to affect your memory," Dr. Smith said. "When sleep is delayed by four hours, you are devastated." Most people have five REM periods a night, he said, but the first two may be more important for retaining memories. When people get those first two periods and are awaken early, he said, their memory is less impaired.

Alcohol tends to disturb the first two REM cycles, making them shorter than normal, Dr. Smith said. "I'm sorry to say there is nothing like going to bed and not drinking if you want to learn."

Nor is there an advantage to delaying sleep deprivation to later in the week, Dr. Smith said. Students were taught a complex task on Tuesday and allowed to sleep normally on Tuesday and Wednesday nights, he said. They were then deprived of sleep on Thursday and showed as much memory loss as if they had stayed up Tuesday night, Dr. Smith said.


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