Studies- Good night's sleep may restore, enhance memories

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 that were 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 Thursday's issue of the journal Nature 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 memories, such as post-traumatic stress disorder.

In separate studies, scientists at the University of Chicago and Harvard Medical School trained college-age people 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. Or, he said, memories could actually be lost during the day, but reconstituted by the brain during sleep.

James L. McGaugh, director of the Center for the Neurobiology of Learning and Memory at the University of California at Irvine, said the voice-recognition training is similar to learning a new language and is therefore more complex than being taught to repeat a simple task.

"These are highly interesting findings that add additional information concerning the effects of sleep on memory," he said. "This takes it to a new level." Still, McGaugh said further experiments are needed to take into account factors that could have influenced the outcome. For example, he said the people trained late at night may have performed better because they went to sleep not long after their training, while their morning-trained counterparts were exposed to an entire day of memories before being tested.

In the Chicago study, one group was trained at 9 a.m., then tested 12 hours later, while a second group was trained at 9 p.m. and then tested the next morning after a night's sleep.

The people tested at night experienced an improvement of 10 percentage points over their pre-training test. But those who had a night's sleep had a 19-point improvement.

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.