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Sleep Strengthens Memory All Through the Night

Jeffrey Ellenbogen always tells his students at Harvard University Medical School to get a good night's sleep before an exam. "If you stay up all night studying for an exam, you might do well on it. After all, studying will help," he observes, but then adds a warning. "Don't expect that memory to last for the up and coming midterm or final exam. Memories without sleep after learning will be weak and vulnerable to forgetting."

That advice is boosted by results of a new study in the journal Current Biology. Two groups of college-aged students memorized word lists and were asked to recall them. One group did the task and was tested later the same day. The other was tested the next morning. "When we compared the group that slept to the group who were awake across the normal day," Ellenbogen says, "what we found was the group who slept were able to remember twice as many words." Then, there was a second test. "We then took an additional group and had them sleep and go the entire next day and we showed that the benefit that sleep provided for these memories - stabilizing them and making them strong - lasted the entire next day as well."

"We know that certain types of cells in the brain become particularly active during sleep and so what this study shows us is that during sleep, cognitive processes are also engaged and in fact, for memory, the cognition can be improved such that our memory can be stronger."

Ellenbogen says the next step is to better understand the brain mechanisms at work. He says animal studies show that memories replay during sleep. He hopes to demonstrate the same process in humans.