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Summary Block 4 The Human Body Problem 7
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Summary for Problem 7 in Block 4 of 1st year psychology
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Problem 7 – PinelStages of sleep – EEG (monitoring method to observe brain’s electrical activity)
There are 4 stages of sleep EEG: After the eyes are shut a person prepare to go to
sleep, alpha waves begin punctuate the low voltage, high frequency waves of alert
wakefulness.
Then the person falls asleep and Stage 1 begins – low voltage high frequency
There is a gradual increase in voltage and decrease in frequency as the person goes
through stages 2, 3 and 4.
Stage 2 has 2 wave forms; K complexes (single large positive wave followed by a
single large negative wave) and sleep spindles (1-2 second waxing and waning burst)
Stage 3 is defined by occasional delta waves – the largest and slowest
Stage 4 is defined by a predominance of delta waves.
Once stage 4 is reached, people stay there for a while and retreat back through the
stages to stage 1. These following periods are emergent stage 1 EEG
After the first cycle – initial stage 1 to stage 4 and back to emergent stage 1- the rest
of the night is spent going back and forth through the stages. Each cycle is about 90
minutes and as the night progresses more time spent in emergent stage 1 and less
time in stage 4.
The sleep associated with emergent stage 1 EEG is called REM sleep. All other stages
of sleep are called non-REM sleep. Stages 3 and 4 together are refereed as slow-
wave sleep (SWS).
During REM: loss of core muscle tone, low amplitude-high frequency EEG, cerebral
activity increases to waking the levels in many brain structures, general increase in
the variability of autonomic NS activity, muscles twitch.
Dreams
80% of awakenings from REM sleep led to dream recall support for REM sleep
correlation with dreaming, but no definite evidence
Modern alternative to Freud’s theory of dreams Hobson’s activation-synthesis
theory: based on the observation that during REM sleep, many brain-stem circuits
become active and bombard the cerebral cortex with neural signals. The information
supplied to the cortex is random and that the resulting dream is the cortex’s effort to
make sense of these random signals.
Why do we sleep?
Recuperation theories of sleep: being awake disturbs the homeostasis of the body
and sleep is required to restore it. These theories vary in terms of particular
physiological disruption they propose as the trigger of sleep. But they all imply that
sleepiness is triggered by a deviation from homeostasis caused by wakefulness and
that sleep is terminated by a return to homeostasis.
Adaptation theories of sleep: sleep is the result of an internal 24-hour timing
mechanism. We are programmed to sleep at night regardless of what happens during
the day. We’ve evolved to sleep at night because sleep protects us from accidents
and predators at night. Some even propose sleep doesn’t have a role in physiological
functioning of the body and that we only do it conserve our energy resources
because we have enough time to do eat, drink and reproduce etc.
, Comparative Analysis
Most mammals and birds sleep, this suggest that sleep serves some important
physiological functioning. Some animals sleep even when it risks predation or evolve
complex mechanism that enable them to sleep.
Sleep is not some special, higher order human function.
Large between-species differences in sleep time suggests that although sleep is
essential, it’s not needed in large quantities.
There isn’t a strong relationship between a species’ sleep time and level of activity,
body size etc. Daily sleep time is related to how vulnerable is it while sleeping and
how much time it must spend time for survival requirements (adaptation theory)
Sleep Deprivation
Less levels of sleep are confounded with high levels of stress
Even moderate amounts of sleep deprivation (3-4 hours less) displays 3 consistent
effects: being more sleepy, displaying negative affect on various tests of mood,
performing poorly of tests of alertness
Effects on complex cognitive functions have been less consistent, only some
functions are susceptible
Effects on physical performance is also inconsistent
Some physiological consequences: reduced body temperature, increases in BP,
decreases in immune functions, hormonal changes, metabolic changes
After 2-3 days of continuous sleep deprivation people experience microsleeps: brief
periods of sleep about 2 to 3 second during which the eyelids droop and people
become less responsive to external stimuli even though they remain standing.
People who are deprived of sleep become more efficient sleepers.
REM sleep deprivation: waking people up each time a bout of REM sleep begins. Has
2 consistent effects: participants have more than their usual amount of REM sleep for
the first 2-3 nights, & with each deprived night there is a greater tendency for REM
sequences, meaning that participants have to be awakened more and more and
there is a compensatory increase in REM sleep. This compensatory increase suggests
that the amount of REM sleep is regulated separately and serves a special function.
Potential role of REM sleep in memory and storage of existing memories?
The default theory of REM sleep: it is difficult to stay continuously in NREM sleep, so
the brain periodically switches to one of two other states. If there are any immediate
needs, the brain switches to wakefulness, if there are no immediate needs, it
switches to REM sleep. REM sleep prepares organisms for wakefulness in natural
environments, where immediate effective activity may be required upon wakening.
Circadian Sleep Cycles
Most species display a regular circadian sleep-wake cycle. Our circadian cycles are
kept on their once-every-24-hour schedule by temporal cues in the environment, the
most important ones being light and dark.
Environmental cues such as light-dark cycle that can control the timing of circadian
cycles are called zeitgebers.
It is possible to lengthen or shorten circadian cycles by adjusting the duration of the
light-dark cycle, e.g. 11.5-11.5 subjects begin to conform to a 23-hour day.
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