Naps boost memory

Washington - Here is some medical advice most people will like: Take a nap.

Interrupting sleep seriously disrupts memory-making, new research suggests. But taking a nap may boost a sophisticated kind of memory that helps a person see the big picture and get creative.

'Not only do we need to remember to sleep, but most certainly we sleep to remember,' Dr William Fishbein, a cognitive neuroscientist at the City University of New York, told a recent meeting of the Society for Neuroscience.

Good sleep is a casualty of the busy modern world. Surveys suggest few adults get the recommended seven to eight hours a night.

Way too little is dangerous: Over time, a chronic lack of sleep can erode the body in ways that leave us more vulnerable to heart disease, diabetes and other illnesses.

Perhaps more common than insomnia, however, is fragmented sleep, the easy awakening that comes with aging, or, worse, the sleep apnea that afflicts millions, who repeatedly quit breathing for 30 seconds or so throughout the night.

Scientists are increasingly focusing less on sleep duration and more on the quality of sleep, what is called sleep intensity, in studying how sleep helps the brain process memories.

Particularly important is 'slow-wave sleep', a period of very deep sleep that comes earlier than better-known REM sleep, or dreaming time.

Dr Fishbein suspected a more active role for the slow-wave sleep that can emerge even in a short power nap. Maybe the brain keeps working during that time to solve problems and come up with new ideas. So he and graduate student Hiuyan Lau devised a simple test: documenting relational memory, where the brain puts together separately learnt facts in new ways.

First, they taught 20 English-speaking college students lists of Chinese words spelled with two characters, such as sister, mother, maid. Then half the students took a nap, being monitored to be sure they did not move from slow-wave sleep into the REM stage.

Upon awakening, they took a multiple-choice test of Chinese words they had never seen before. They did much better at automatically learning that the first of the two-pair characters in the words they had memorised earlier always meant the same thing - female, for example.

'The nap group has essentially teased out what's going on,' Dr Fishbein concludes. These students took a 90-minute nap, quite a luxury for most adults. But even a 12-minute nap can boost some forms of memory, adds Dr Robert Stickgold of Harvard Medical School.

Conversely, Wisconsin researchers briefly interrupted night-time slow-wave sleep by playing a beep - just loudly enough to disturb sleep but not awaken - and found those people could not remember a task they had learnt the day before as well as those whose slow-wave sleep was not disrupted.

None of the new work is enough, yet, to pinpoint the minimum sleep needed for optimal memory. What is needed may vary considerably from person to person.

The findings do suggest some practical advice: Get apnea treated. Avoid super-late nights followed by sleep-in weekends. And do not feel guilty for napping.

Associated Press