Why we remember more after sleep
AIt has long been known that people who sleep after learning something recall it better than those who stay awake for the same period. For much of the twentieth century this was explained simply: sleep protects new memories from interference, because while we are unconscious nothing new competes for attention. More recent research suggests that sleep plays a far more active role.
BRecordings of brain activity in rats that have learned to run through a maze show that, during deep sleep, the same groups of neurons that fired during the task fire again in the same order, only faster. Researchers call this replay. In humans, experiments in which a sound or smell present during learning is presented again during deep sleep have found that the associated memories are strengthened, suggesting that replay can be triggered deliberately.
CDifferent stages of sleep appear to support different kinds of learning. Deep, slow-wave sleep, which dominates the early part of the night, seems particularly important for facts and events. Rapid-eye-movement sleep, which becomes longer towards the morning, has been linked to emotional memories and to finding hidden patterns in information. Cutting a night short may therefore affect some kinds of learning more than others.
DThese findings have practical implications, though they are sometimes exaggerated. Commercial devices that promise to ‘teach you while you sleep’ have little evidence behind them: sleep appears to strengthen what has already been learned, not to install new knowledge. What the research does support is less exotic advice — that students who give up sleep to study late into the night may be undermining the very learning they are trying to achieve.