THE NEW ZEALAND HERALD 26Th NOVEMBER 2008
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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 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, said at a meeting of the Society for Neuroscience.
Surveys suggest few adults attain the recommended seven to eight hours sleep a night. Too little is dangerous as sleep deprivation causes car crashes and other accidents. Over time, a chronic lack of sleep can erode the body leaving 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 ageing, or, worse, the sleep apnoea that afflicts millions, who repeatedly stop breathing for 30 seconds or so throughout the night.
Increasingly, scientists are 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 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.
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 learned the day before as well as people whose slow-wave sleep was not disrupted.
Fragmented sleep, whether from ageing or apnoea, 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, Dr McGinty mimicked human sleep apnoea 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, Dr McGinty let the rats sleep peacefully for as long as they wanted for the next two weeks.
The catch-up sleep did not help: rested rats used room cues to quickly learn the escape hole in a maze. Those with fragmented sleep two weeks earlier could not, only randomly stumbling on 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 an efficient deep sleep even if they sleep only four hours,” notes Dr Chiara Cirellia of the University of Wisconsin, Madison.
The findings suggest people should get apnoea treated, avoid “sleep bulimia”, super-late nights followed by sleep-in weekends, and don’t feel guilty for napping.AP
It is well documented that a lack of sleep can often be a trigger for Psychosis.