Getting a good night’s sleep before a big exam might be better than pulling an all-nighter.

A study found that sleep apparently restores memories lost during a hectic day.

It’s not just a matter of sleep recharging the body physically. Researchers say sleep can rescue memories in a biological process of storing and consolidating them deep in the brain’s complex circuitry.

The finding is one of several conclusions made in a pair of studies in today’s issue of the journal Nature, www.nature.com, that look at how sleep affects memory.

The researchers said the findings may influence how students learn, and someday could be incorporated into treatments for mental illnesses involving memory such as post-traumatic stress disorder.

In separate studies, scientists at the University of Chicago and Harvard Medical School trained college students to perform specific tasks, then tested them to see how much they recalled after either a night’s sleep or several hours awake.

The Chicago study found that test subjects who had been taught to recognize a voice synthesizer’s murky speech understood more words after a night of sleep than counterparts who were tested hours after the training with no sleep.

"We all have the experience of going to sleep with a question and waking up with the solution," said Daniel Margoliash, a professor of neurobiology at the University of Chicago.

Margoliash said it could be that a person acquires so many memories each day that some details are lost in that jumble, but that the brain sorts and organizes the memories during sleep.

In the Harvard study, scientists trained 100 people ages 18 to 27 to perform finger-tapping sequences similar to learning piano scales. Their ability to repeat those sequences was then tested at various intervals, including after one and two nights of sleep. Sleep was found to sharpen a person’s performance the next day.

The researchers found evidence that memories are consolidated in stages in a process similar to storing data on a computer’s hard drive. The second stage requires sleep.

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