Sleep and Memory

For a long time, sleep was thought of as a period when the brain simply rests. Research over the past century, however, suggests that sleep plays an active role in memory. In a well-known study from 1924, two American psychologists asked people to memorize lists of nonsense syllables. Participants who slept after learning the lists remembered more of them than participants who stayed awake for the same amount of time.

At first, researchers explained this result in a simple way: people who were asleep did not experience new events that could interfere with what they had just learned. Later studies pointed to a more active process. When scientists recorded the brain activity of rats as they ran through a maze, they found that the same patterns of activity appeared again while the animals slept, as if the brain were replaying the experience.

Many researchers now believe that this replay helps move new information from temporary storage into more permanent memory. This may explain why students who stay up all night before an exam often do worse than they expect. Without sleep, much of what they studied may never be stored properly.