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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.
[Associated
Press;
Lauran Neergaard covers health and medical issues for The Associated Press in Washington.
Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
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