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Just Sleep on It

News & Features | December 9, 2009

For many college students, a good night’s sleep is often just four and a half hours long on a lumpy dorm mattress after a night fueled by a few mugs of tar-black joe. Anyone who has ever raced to finish a paper before being evicted from the quiet reading room into the three AM chill might reasonably curse the day that the phenomenon of sleep was imposed upon humanity.

But a recent study suggests a unique way that sleep can be linked to knowledge retention. Scientists at Northwestern University have reported that playing specific sounds while people slept helped enhanced their memories of individual facts.

Participants in the study were taught to move 50 pictures to assigned locations on a computer screen. Each picture was associated with a different sound. Then the subjects took a nap for 90 minutes or less, during which they heard sounds from some of the pictures. When the participants awoke, none of them could recall which sounds had been played for them, but almost all of them could better remember the correct placement of the pictures for which they had heard the sound cues while they were sleeping.

The study offers more evidence that information can get to the brain even while you sleep. Sleepers are also more sensitive to certain sounds, perhaps jerking awake at the sound of a baby’s whine or an unfamiliar voice. An earlier study had shown that participants who learned a task while smelling a rose scent remembered the task better if they smelled the same scent while they slept. This new research suggests, perhaps for the first time, that very specific memories can be singled out and enhanced during sleep.

While the new sound study might crack open doors to new methods of enforcing knowledge, Tufts professor of biology Harry Bernheim stressed that the study in no way suggests that people can learn in their sleep. “New skills must be learned the old fashioned way: while you are awake and devoting strict attention to the material,” Professor Bernheim wrote in an email. “As Euclid I believe said, ‘There is no royal road to learning geometry’—or anything else for that matter.”

The Northwestern study also contributes to a theory that sleep allows the brain to consolidate memories and process information. Earlier work has suggested that people are better able to remember things if they sleep soon after learning it. Another study, published in the Proceedings of the National Academy of Sciences in 2007, showed college students pairs of elaborately decorated ovals and told them that for each pair, one oval would win out over the other but were not explained the broader hierarchy of the ovals. The students were then tested on how much of the hierarchy they could unravel, with some students given the chance to sleep before they were tested. The students who had slept were better able to make out the pattern. The study shows how “sleeping on it” can allow the brain to unearth sequences and insights.

The study did not impress everyone. Some neuroscience experts said that the study’s effects were too minor to be significant, especially because subjects who were reminded of the sound cues while they were awake did about as well as the sleeping subjects. The study’s authors responded that the study was significant because it showed that this process of recollection could also happen during sleep.

Burdensome though sleep may seem, it may have originally made evolutionary sense. A paper published last August argued that sleep evolved to keep us tucked safely in bed while the predators lurked outside. Sleep also may have evolved to help organisms conserve energy when resources are scarce. Energy metabolism, caloric demand, and body temperature all decrease when we sleep. It may also exist to give bodies a chance to restore what was lost or damaged when awake. Studies have linked sleep to a stronger immune system against colds, and many findings suggest that vital functions such as tissue repair and muscle growth occur mostly during sleep.

Delicious and fair-trade though that seventh latte may be, sleep has its benefits as well. Maybe if students can manage to associate their Chinese flash cards with different frog calls, they will finally get some much-needed—and potentially productive—shut-eye.