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Sleep can be split into stages of
different brain activity
These are the stages of slow wave sleep:
Stage 1, is a bit like deep relaxation, with a lower heart rate,
muscle tension and temperature. It is still easy to wake people
up during this stage of sleep.
Stage 2, has a slower and larger EEG waves, with some quick
bursts of high frequency waves called sleep spindles.
Stage 3, has even larger slower waves.
Stage 4, has the largest, slowest waves of all, because it's the
deepest stage of sleep. Metabolic activity is pretty low in
general, and the sleeper is very hard to wake during this stage
of sleep.…read more

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Sleep can be split into stages of different
brain activity, continued
Electroencephalograms (EEGs) measure electrical activity
in the brain and are used to record the stages of sleep.
As you fall into deeper sleep, brain activity becomes higher
voltage and lower frequency.
After stage 4 the cycle of sleep reverses back through stages 3
and 2. A period of active sleep occurs instead of stage 1.
During the active stage, metabolic activity increases, and the
body appears to be almost paralysed except for rapid eye
movement (REM). The EEG pattern is almost the same during
REM sleep as when you are awake. The cycle is repeated
about 5 times during the night, but we only enter stages 3 and 4
in the first two cycles. Periods of REM increase with each cycle.…read more

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Evolutionary approaches to sleep
Evolutionary approaches relate to the environment, evolution and
survival of the fittest.
Webb (1968) suggested that everyday sleep is similar to hibernation
­ sleep conserves energy at times when it's harder to get resources
(e.g. night time). Using energy would be inefficient.
Meddis (1977) suggested that sleep helps keep animals safe. By
being quiet and still, they are less likely to attract predators
(especially at night). However, sleep also makes animals vulnerable
to predators if discovered.
Not sleeping at all would be very advantageous, but as it seems to
occur in all animals, it must have an important function- although how
much sleep animals have varies. Animals that graze often and must
avoid predators sleep less, while predators that don't eat as
frequently and aren't hunted, sleep more.…read more

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Evolutionary approaches evaluation
The evolutionary approach, focusing on survival
and environmental adaptation, is useful for
understanding how and why behaviours occur.
Behaviours have evolved to help survival and
adapt us to our environment.
Evolution occurs over long periods so it's hard
to test theories about why some behaviours
have been naturally selected. So, it is difficult to
falsify them, making them less useful from a
scientific perspective.…read more

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Restoration approaches to sleep
Restoration approaches suggest that sleep restores the
body's ability to function, after being busy during the day.
Oswald (1980) suggested that SWS/non-REM sleep is for
restoring bodily functions linked to physical activity, and
REM sleep is for restoring brain function.
Horne (1988) distinguished between two types of sleep:
core sleep, which is made up of stage 4 SWS (for body
restoration) and REM sleep (for brain restoration), and
optional sleep, which is made up of the other stages of
sleep. Although optional sleep is not necessary, having it
can help conserve energy.…read more

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