Sleep, Gender and Aggression Notes

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Biological Rhythms & Sleep
The Circadian Rhythm
The Sleep Wake Cycle
o Guided by external cues; knowing the time of day and feeling tired when it gets dark. The
endogenous clock works without cues, setting the cycle for 24-25 hours. External cues
(E.g. daylight) help to adjust the internal clock to the environment. Circadian rhythms
continue to work despite the isolation from natural light. They also show how external
cues are important because the clock was not perfectly accurate it varies by day.
1. Supporting for a Free Running Rhythm ­ Siffre spent 61 days I the Southern Alps 1962, and
resurfaced on 17 September believing the date was 20th August. In 1975, he spent 205 days in a
cave in Texas. He found that his natural circadian settled down to just over 24 hours, although it
could range to 48 hours. In 1999 he made his final underground stay and found that his internal
clock ticked far slower compared to when he was younger.
2. Aschoff and Wever (1976) ­ Supported Siffres research with their own. They placed pp's in an
underground WW1 bunker away from any external cues. They found that most pp's displayed
circadian rhythms between 24 and 25 hours in length, although some were 29 hours. This shows
that the cycle operates in the absence of external cues, and that the natural free-running cycle is
about 24-25 hours.
3. Importance of External Cues ­ Folkard (1985) gathered 12 volunteers to spend 3 weeks in
isolation with no natural light. They were instructed to go to bed when the clock indicated
7:45am. The clock was sped up so that when it looked like there was 24 hours passing; only 22
hours actually had. To begin with pp's cycles matched the clock, but when it quickened it
returned to 24 hours. This suggests that the circadian rhythm can only be guided to a limited
extent by external cues.
4. Research Methodology ­ Pp's were isolated from clocks, radios and daylight. However they were
not isolated from artificial light, as it was thought that dim light did not affect the circadian
rhythm . Czeisler et al. (1999) altered pp's circadian rhythm down to 22 hours and 28 hours just
using dim light.
5. Individual Differences ­ One difference is the length of a person's cycle; Czeisler et al. (1999)
found that cycles can vary from 13-65 hours. The other difference is related to the cycle onset.
Individuals appear to be innately different in terms of when their cycle peaks. Duffy (2000) found
that morning people rise early and go to bed early, whereas evening people prefer to go to bed
and wake later.
Core Body Temperature
o Temperature of the body is at its lowest at 4:30am and highest at 6:00pm. Slight dip just
after lunch ­ a bi-daily rhythm.
1. Effects of Core Body Temperature Changes ­ Folkard et al. (1977) looked at the learning ability of
12-13 year old children who had stories read to them at either 9am or 3pm. The afternoon group
showed superior recall and comprehension, retaining 8% more meaningful material. This
suggests that long term recall is best when the body temperature is highest.
2. Cause or Correlation ­Giesbrecht et al. (1993) lowered body temperature by placing pp's in cold
water and found that cognitive performance was worse on some tasks. Hord and Thompson

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Ultradian & Infradian Rhythms
Ultradian Rhythms
o Sleep Stages
Stages 1 + 2 ­The brain produce a typical pattern called a BETA wave. As you
become more relaxed, your waves become more slow and regular (Alpha
waves). Waves then slow further as you fall asleep and have a greater frequency
(Theta waves). THETA waves are made with bursts of activity of increased
wave frequency ­ sleep spindles.
Stages 3 + 4 ­ Characterised by Delta waves. These stages are slow wave sleep
(SWS).…read more

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Two weeks after ovulation, if there is no pregnancy, progesterone is reduced and
this caused the lining of the womb to be shed.
1. Exogenous Cues ­ Research has shown that women who live together (and do not take
contraceptives) tend to menstruate at the same time every month. Russel et al. (1980) took
daily samples of sweat from one groip of women and rubbed iit onto the upper lip of women
in a second group.…read more

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Murphy (1998) found that if you shine a light on the back of pp's knees, it shifts their
circadian rhythm.
o Social Cues ­ Biologists believe that social cues were the main zietgebers for human
circadian rhythms. Our daily rhythm appeared to be entrained by social convention, not
internal biology. We eat meals at socially determined times ­ the zietgeber for cells in the
liver and heart are likely to be meal times because they are reset by eating.…read more

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Sleep Patterns ­ Sleep is an adaptive mechanism that makes their parents lives easier.
Daytime sleep allows parents to carry out chores ­ enhancing survival. Night waking ensures
that the bay is fed regularly, forcing the parent to acknowledge their cold and hungry state.
2. REM Sleep ­ An infant's greater amount of REM sleep can be explained in terms of the
relative immaturity of the infant brain, relating to the considerable amount of learning
occurring.…read more

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Reduced Sleep ­ This is partly due to physiological changes as well as actual problems staying
asleep. Problems staying asleep are also explained by the fact that deep sleep is reduced in
old age.
4. Explanation of Old Age ­ Reduction in SWS leads to a reduced production of growth
hormone. This may explain some of the symptoms associated with old age (lack of energy,
lower bone density).…read more

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The Nature of Deindividuation
o Characteristics ­ Low self-evaluation and decreased concern about the evaluation of
others. This leads to an increase in behaviour that is not normally inhibited by social
o Factors ­ Anonymity and altered consciousness due to drugs or alcohol. Zimbardo (1969)
stressed that these conditions may lead to `prosocial behaviour', however the focus on
deindividuation is almost exclusively on `antisocial behaviour'.…read more

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Lack of Support ­ A meta-analysis of 60 studies concluded that there is insufficient support
for this theory. Postmes and Spears (1998) found that disinhibition and antisocial behaviour
are not more common in large groups and anonymous settings. Neither was there much
evidence relating to reduced self-awareness.
3. Pro-social Consequences ­ An increase in prosocial behaviour could be the result of
deindividuation, depending on situational factors.…read more

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Poole and Regoli, as they found that the best indicator of
violence among juvenile offenders was pre-institutional violence.
o Stages in the process
Difficult social conditions
= Scapegoating of less powerful group
= Negative evalution and dehumanisation of target group
= Moral values and rules becoming inapplicable and the killing begins
= The passivity of bystanders
o Dehumanisation ­ Human beings have moral inhibitions about killing humans, however
this changes if the target is dehumanised and are seen as animals.…read more

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Popova et al. suggested that in animals, they are selectively bred for
domestication and for increasingly docile temperaments ­ there is an increasing
concentration of serotonin.
2. Evidence from Antidepressants ­ Low levels of serotonin are associated with low impulse
control and aggressive behaviour, and so drugs that clinically raise serotonin levels should
lower aggression. Bond supports this, in that antidepressants elevate serotonin levels.…read more


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