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You snooze, you improve—your memory, that is, according to a new study published this week in Current Biology.
Researchers from BWH, Harvard Medical School and the University of Pennsylvania for the first time have demonstrated that sleep promotes the strengthening of declarative memories, or memories about facts and events (as opposed to how-to memories, like how to play a piano sequence).
The study shows that sleep is not an inactive state. “That’s an obsolete concept,” Jeffrey Ellenbogen, MD, associate neurologist at BWH and a postdoctoral fellow in sleep medicine at HMS, said. “The brain is doing lots of things during sleep, including consolidating memory. The basic take-home message is that you need to get sleep on a regular basis in order to maximize memory.”
The findings are especially important for those with mentally demanding lifestyles, like college students and medical residents, who often do not get enough sleep. The study also reinforces that there is no substitute for sleep. “Taking a stimulant to stay awake can help with alertness in the short term, but people really need sleep to retain knowledge and function at their best,” Ellenbogen said.
To determine whether sleep benefits memory, Ellenbogen and his team assigned 60 healthy, college-aged subjects into four groups in the initial phases. Each group learned 20 pairs of words equally. Prior to testing, two of the groups slept overnight and two of the groups were awake during the day. Half of the subjects then were tested with cued recall, whereas the other half learned another list of words immediately before testing (so-called interference). While the sleep group performed slightly better than the wake group when tested with simple cued recall, interference testing unmasked a large benefit of sleep. A fifth group of 12 subjects was then added. This group learned at night, slept and then went the entire next day awake before testing. Their performance was just as good as the sleep group, showing that the effect of sleep was independent of the time of day of testing and that it was a long-lasting benefit.
Ellenbogen hopes the study will alert the academic community to the critical benefit sleep plays in learning, which is of particular importance to medical residents and college students notorious for cramming the night before a big exam. Ellenbogen plans to conduct a follow-up study on how much sleep is necessary.