Discuss the role of neural and/or hormonal mechanisms in aggression. (8 marks + 16 marks)

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Jessica Higgins
Psychology ­ Mrs Grant
Q: Discuss the role of neural and/or hormonal mechanisms in aggression. (8 marks + 16
Two explanations of aggression come from the role of neural and hormonal mechanisms.
Neurotransmitters are chemicals that allow impulses in one area of the brain to be transmitted to
another area. Two neurotransmitters in particular are thought to be important in the control of
aggressive behaviour, these are serotonin and dopamine.
Low levels of serotonin have been associated with increased aggression levels. In normal
levels, it is thought that serotonin has a calming, inhibitory effect on neuronal firing in the brain
however low levels remove this inhibitory effect and so individuals are less able to control their
impulsive and aggressive responses. Some drugs are thought to alter serotonin levels and thus
increase aggressive behaviour. Mann et al. (1990) gave 35 participants a drug which decreased
serotonin levels and by using a questionnaire, found an increase in hostility and aggression scores.
However, there are methodological issues involved with this study, in particular with the
measurement of aggression. Using a questionnaire could lead to social-desirability bias and in
particular is more likely with sensitive topics such as aggression. Individuals are more likely to
under-report undesirable behaviour such as aggression and over-report desirable behaviour leading
to invalid findings.
Dopamine is the other neurotransmitter associated with aggression however, unlike
serotonin, high levels of dopamine are associated with increased aggression. Although the link
between dopamine and aggression is not as well established, there is evidence to suggest such a link
exists. The use of amphetamines increases dopamine activity and it has also been found to increases
in aggressive behaviour. Antipsychotics which reduce dopamine however, have been shown to
reduce aggression, thus supporting this explanation.
Ferrari et al. (2003) allowed a rat to fight every day for 10 days at exactly the same time
each day. On day 11 they denied the rat the chance to fight, but instead measured the levels of
serotonin and dopamine. It was found that in readiness for a potential fight, the rat's brain showed
increased levels of dopamine and decreased levels of serotonin. From this we can conclude that the
experience had changed the rat's brain chemistry so that it was ready for aggression. It clearly
implicates serotonin and dopamine in the process of getting ready to be aggressive. However, this
study can be criticised for its unethical procedure in forcing a rat to fight as it may be inflicting
permanent physical or psychological harm, it can also be said that this study lacks ecological validity
as it cannot be generalised to humans.
Evidence from other non-human studies also supports this theory. Raleigh et al. (1991) found that
monkeys fed on a diet which decreased their serotonin levels increased their aggressive behaviour
however, on a diet that increased serotonin levels, the monkeys displayed reduced aggression. It is
hard to generalise these findings to humans however, as many animals do not have the same
capacity for cognitive processing and self-awareness and animal behaviour tends to rely more on
biological factors.
Testosterone is a hormone produced in the male testes and has been linked to aggression,
as it plays a part in increased muscle and bone mass, this suggests that it plays a structural role in

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Jessica Higgins
Psychology ­ Mrs Grant
influencing aggression. Testosterone has been shown to correlate with the level of aggression
displayed by humans and animals; it is also believed to reduce levels of available serotonin.
There have been many experiments done to test the effects of adding and removing
testosterone. All of which have been performed on animals due to methodological and ethical issues
with testing on humans.…read more

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Jessica Higgins
Psychology ­ Mrs Grant
the sole cause of aggression, we would see a worldwide distribution of aggression.…read more


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