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Although no one knows for
sure why we sleep, there are a number of theories. Sleep may have
evolved to protect animals from their predators by reducing their
activity during the times when they are most vulnerable.
Research has shown that REM and NREM sleep may serve specific
biological functions. Sleep deprivation studies reveal that humans
and other animals respond to sleep loss in the same way. When study
subjects are deprived of REM sleep, they tend to spend longer
periods in REM sleep during their next sleeping period to make up
for the loss. REM sleep after deprivation is more intense, with more
eye movements per minute than in normal REM sleep. Similarly,
subjects deprived of NREM sleep usually spend more time in NREM
sleep afterward. EEGs measuring brain activity show that this
rebound NREM sleep also differs from normal NREM sleep. This
research suggests that the body needs adequate levels of both REM
and NREM sleep. This conclusion has led many sleep researchers to
believe that the two kinds of sleep serve different biological
purposes, although the exact functions remain unclear.
The relationship between maturity at birth and REM sleep suggests
that REM sleep plays a role in the development of the brain. REM
sleep may have a related function later in life as well. However,
that function remains a mystery. |
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