Neural and hormonal mechanism in aggression

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Discuss the role of neural and hormonal mechanisms in aggression (24
marks)
Aggression in humans associated with high levels dopamine, low levels serotonin. Serotonin has a
calming effect which inhibits aggression so when levels low people less likely to control aggressive
behaviour. Brown et al. 1992 low levels of waste product of serotonin in cerebrospinal fluid of
individuals who are prone to impulsive and aggressive behaviour.
Mann gave 35 healthy male and female participants dexfenfluramine which lowers levels of
serotonin in brain. He then gave them a questionnaire to assess their aggression and hostility
scores and found that dexfenfluramine treatment in males but not females was associated with
high aggression and hostility scores. Although this study demonstrates the importance of
neurotransmitters in aggression, it also suggests that nurture (environment) is just as important
as women may not display the behaviour because of social norms, they may however feel it. Such
a study of so few pps may not be generalizable and of course is also unethical ­ potentially could
cause psychological harm.
There is further research support for the role of serotonin in aggression. Aurora and Meltzer did a
meta-analysis of 29 studies of serotonin and aggression showed that low serotonin was linked to
antisocial children and adults. In particular there was low levels serotonin in those who had
attempted suicide. This demonstrates that there is a link between neurotransmitter imbalances
and impulsive behaviour and so provides reliable evidence to support this claim.
Ferrari et al. stated that causation may in fact work the other way round. They did a study using
one rat and allowed the rat to fight at the same time every day for 10 days. But on the 11th day
they found that the rat learned from experience and had heightened levels of serotonin in
anticipation of fight. This demonstrates that repeated aggression in fact causes neurotransmitter
imbalance rather than the other way round. Such a study of course involves the unethical use of
animals in a situation where the benefits aren't particularly high or the results surprising. Can we
extrapolate from rats to humans in any case ­ we have free will and can stop ourselves often from
engaging in such behaviour in any case. Human aggression is incredibly complex, unlike rat
aggression and involves many decisions and the influence of how we have been socialized for
example.
Testosterone has also been associated with aggressive behaviour, though most studies
correlational only. For example, in a meta-analysis, Archer found a low positive correlation
between testosterone and aggression.
Kouri et al's study supports the link between testosterone and aggression. Pps were given
testosterone or a placebo and told that by pressing a button they could receive an amount of cash
that another pp was receiving on the other side of the wall. The set up made it seem as if the
other pp was pressing the button to get cash and it was observed how much the naive pp pressed
the button. Those who received the testosterone pressed the button more than those with the
placebo. An advantage of this study is the experimental method allows us to demonstrate cause
and effect relationship. However the situation is an artificial one and lacks mundane realism ­such
situations rarely happen in real life. There may also have been demand characteristics as pps may

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Research into testosterone and aggression however is far from conclusive. Albert et al. found that
even though studies have demonstrated a link between testosterone and aggression other studies
in fact have found no such relationship in particular those who compared violent and non-violent
individuals. Bain et al. also found no differences in testosterone levels of violent and non-violent
criminals.
There is also a gender bias in research on testosterone and aggression as research tends to
concentrate only on testosterone in males.…read more

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