Looking to improve your memory? Consider a short 45-minute "power nap," say German researchers who found that a daytime snooze can help you brain retain things it's learned.

The memory boost accompanies other benefits of some afternoon shut-eye, such as stress relief, mood improvement and increased productivity, they say.

While previous studies have shown that sleep can improve memory, the new study reported in the journal Neurobiology of Learning and Memory suggests even a short nap can aid the process in which learned information is moved into long-term memory storage areas in the part of the brain known as the hippocampus.

For the study, researchers at the Saarland University in German divided a collection of students into two smaller groups, each of which was tasked with learning 90 single words and 120 word pairs.

Since the word pairs were largely meaningless combinations the students would have never heard before — such as "milk-taxi" — they would have to access a memory of them in the hippocampus to recall them later.

After learning the words and the word pairs, one group watched DVDs as the other group took an hour-long nap, then both groups were tested on their ability to recall words.

The DVD group's recall was significantly worse than the napping group when tested on the word pairs, researchers say.

"The memory performance of the participants who had a power nap was just as good as it was before sleeping, that is, immediately after completing the learning phase," says study lead author and neuropsychologist Axel Mecklinger.

"Even a short sleep lasting 45 to 60 minutes produces a fivefold improvement in information retrieval from memory," he says.

The researchers used electroencephalogram (EEG) tests in an effort to find out the mechanism by which napping was helping with memory.

They focused on a particular kind of brain activity known as "sleep spindles," a brief burst of activity that showed up on the EEG tests.

"The hippocampus, when awake, reactivates the neural firing pattern that was also active during learning," Mecklinger says. "This replay may produce 'tags' which are then used for consolidation during sleep."

The findings may not be much help for Americans, 50 percent of whom say they don't get enough sleep.

A 2011 survey of U.S. businesses found that only 6 percent provided nap rooms or areas for their employees.

Experts in sleep medicine said the findings of the new study are more evidence of the important benefits of sleep.

"Sleep and memory are very much linked with good evidence for the benefits of sleep on memory consolidation," says Adrian Williams, a professor of sleep medicine at King's College London. "So, our grandmothers were right — sleep on it."

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