Nap without guilt: It boosts sophisticated memory

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Nap without guilt: It boosts sophisticated memory

WASHINGTON - Just in time for the holidays, some medical advice most people will

like: Take a nap. Interrupting sleep seriously disrupts memory-making,

compelling new research suggests. But on the flip side, taking a nap may boost a

sophisticated kind of memory that helps us see the big picture and get creative.

" Not only do we need to remember to sleep, but most certainly we sleep to

remember, " is how Dr. Fishbein, a cognitive neuroscientist at the City

University of New York, put it at a meeting of the Society for Neuroscience last

week.

Good sleep is a casualty of our 24/7 world. Surveys suggest few adults attain

the recommended seven to eight hours a night.

Way too little clearly is dangerous: Sleep deprivation causes not just car

crashes but all sorts of other accidents. 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.

But perhaps more common than insomnia is fragmented sleep - the easy awakening

that comes with aging, or, worse, the sleep apnea that afflicts millions, who

quit breathing for 30 seconds or so over and over throughout the night.

Indeed, scientists increasingly are focusing less on sleep duration and more on

the quality of sleep, what's called sleep intensity, in studying how sleep helps

the brain process memories so they stick. Particularly important is " slow-wave

sleep, " a period of very deep sleep that comes earlier than better-known REM

sleep, or dreaming time.

Fishbein suspected a more active role for the slow-wave sleep that can emerge

even in a power nap. Maybe our brains keep 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 learned 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 didn't move from slow-wave

sleep into the REM stage.

Upon awakening, they took a multiple-choice test of Chinese words they'd never

seen before. The nappers did much better at automatically learning that the

first of the two-pair characters in the words they'd memorized earlier always

meant the same thing - female, for example. So they also were more likely than

non-nappers to choose that a new word containing that character meant " princess "

and not " ape. "

" The nap group has essentially teased out what's going on, " 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. Stickgold of

Harvard Medical School.

Conversely, Wisconsin researchers briefly interrupted nighttime slow-wave sleep

by playing a beep - just loudly enough to disturb sleep but not awaken - and

found those people couldn't remember a task they'd learned the day before as

well as people whose slow-wave sleep wasn't disrupted.

That brings us back to fragmented sleep, whether from aging or apnea. It can

suppress the birth of new brain cells in the hippocampus, where memory-making

begins - enough to hinder learning weeks after sleep returns to normal, warns

Dr. Dennis McGinty of the University of California, Los Angeles.

To prove a lasting effect, McGinty mimicked human sleep apnea in rats. He hooked

them to brain monitors and made them sleep on a treadmill. Whenever the monitors

detected 30 seconds of sleep, the treadmill briefly switched on. After 12 days

of this sleep disturbance, McGinty let the rats sleep peacefully for as long as

they wanted for the next two weeks.

The catch-up sleep didn't help: Rested rats used room cues to quickly learn the

escape hole in a maze. Those with fragmented sleep two weeks earlier couldn't,

only randomly stumbling upon the escape.

None of the new work is enough, yet, to pinpoint the minimum sleep needed for

optimal memory. What's needed may vary considerably from person to person.

" A short sleeper may have a very efficient deep sleep even if they sleep only

four hours, " notes Dr. Chiara Cirellia of the University of Wisconsin, Madison.

But altogether, the findings do suggest some practical advice: Get apnea

treated. Avoid what Harvard's Stickgold calls " sleep bulimia, " super-late nights

followed by sleep-in weekends. And don't feel guilty for napping.

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EDITOR'S NOTE - n Neergaard covers health and medical issues for The

Associated Press in Washington.

By LAURAN NEERGAARD AP Medical Writer

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