Five-minute power nap sharpens your memory

London: Nodding off refreshes the brain and improves the memory, research has shown.

The findings suggest it is falling asleep, not being asleep, that is beneficial.

Napping for just 10 minutes reduces drowsiness, even though most studies suggest that more sleep time is needed.

A German team has explained this anomaly by demonstrating that the act of falling asleep sharpens the memory.

Dr Olaf Lahl, from the University of Dusseldorf, asked students to memorise a list of words and recall it after an hour spent playing solitaire.

Some of the students were allowed a five-minute nap at the start, and they recalled significantly more words. "It seems that much more is happening during the initialisation of sleep than we once thought," Dr Lahl told New Scientist magazine. "Maybe much of sleep's functional aspects are accomplished at its very beginning."

Thoughts go crazy

Dr Robert Stickgold, from Harvard University, said researchers underestimated the importance of napping. Just before sleep, the brain "replays" recent events, producing dreamlike sensations and "crazy" thoughts, he says.

He suggests that this could explain the benefit of the power nap.

"It's as if the brain is sifting through new material to figure out what to work with," he said. This short period of "thought marshalling" rather than prolonged sleep may be crucial for good recall.

The scientists suggest that after "nodding off", further sleep may not be necessary. "You might not even need sleep after that hypnagogic period," said Dr Stickgold.