Naps can help: Fresh evidence that brains need deep sleep for good memories

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Fresh evidence that brains need deep sleep for good memories _ and

naps can help

By LAURAN NEERGAARD

AP Medical Writer

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WASHINGTON (AP) -- 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.

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

The Associated Press in Washington.