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- NEW YORK (Reuters
Health) - ``To sleep: perchance to dream: ay, there's the rub,'' wrote
Shakespeare in ``Hamlet.'' But dreaming is not the only thing the brain
does while we catch our ZZZ's. Study findings suggest that as our bodies
sleep, our brains may be hard at work ``replaying'' the events of the day--sorting
them out and consolidating them into the manageable chunks of information
that form our memories.
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- Researchers have hypothesized that one function of sleep
is to stabilize the brain connections that store recently learned information.
Studies in rats have supported that concept. Now, in the August issue of
Nature Neuroscience, investigators report evidence that sleep solidifies
memory in humans as well.
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- Dr. Pierre Maquet of the University College London, UK,
and colleagues used a technique called positron emission tomography to
monitor brain activity during sleep and wakefulness in three groups of
volunteers. Two groups went through several hours of training sessions
that challenged their reaction times to stimuli that appeared on a computer
screen. One group had their brain activity monitored during the session
while in the other group, brain activity was measured later during sleep.
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- In both groups, reaction times decreased--that is, got
better--with practice. Moreover, the subjects' skills improved further
after a night's sleep, suggesting that they ``refined'' their skills overnight,
Maquet's team reports. When the researchers studied the brain scans and
compared them with scans from untrained subjects, they found evidence that
nighttime learning did take place. During REM sleep--the period in which
dreams take place--the trained subjects showed significant activity in
the same brain areas that had been active as they performed the learning
tasks.
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- ``Waking experience influences regional brain activity
during subsequent sleep,'' the authors conclude.
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- This, Maquet's team writes, supports the theory that
the experiences of waking life determine which brain areas are reactivated
during sleep. Although it is unclear why this happens, the researchers
speculate that REM sleep may be a period of ``memory consolidation''--a
process in which new, ''fragile'' memories are replayed and processed.
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