Hormonal & Neural mechanisms in aggression

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Neurotransmitters are chemicals in the brain that allow impulses from one part of the brain to be
transmitted to another area. All behaviour is influenced by the action of neurotransmitters. Two
neurotransmitters are believed to be particularly important in the control of aggressive behaviour.
Aggression in both animals and humans has been associated with:
Low levels of serotonin
High levels of dopamine
(Cases) ­ Serotonin in normal levels exerts a calming, inhibitory effect on neural firing in the
brain. Psychologists believe that low levels of serotonin, known as the body's natural `happy drug',
can lead to an increase in aggression levels. This is because serotonin is thought to inhibit our
response to emotional stimuli that might otherwise lead to aggressive behaviour, so low levels of
serotonin mean we will respond aggressively more often. Low levels of serotonin in the brain have
been associated with an increased weakness to impulsive behaviour, aggression and violent suicide.
(Mann) ­ Some drugs are thought to alter serotonin levels and increase aggressive behaviour.
Mann gave 35 healthy p.ps a drug which is known to reduce serotonin. Using a questionnaire
to assess hostility and aggression levels, they found that the drug treatment in males (but not
females) was associated with an increase in hostility and aggression scores. However, this
was only found in males.
Bond (2005) ­ said that if low levels of serotonin cause aggression then drugs that increase the
level of serotonin should result reduced aggression, and her research found exactly this. She
found that this is what happened in clinical studies of antidepressant drugs that elevate
serotonin levels. She established that such drugs do tend to reduce irritability and impulsive
Raleigh et al ­ support the importance of serotonin in aggressive behaviour in a study on
monkeys. They found that individuals fed on experimental diets high in a drug that increases
serotonin levels in the brain, suggesting that the difference in aggression can be attributed to
their serotonin levels however this study in specie specific ­ different biology.
We are unsure of whether there is a causal link between dopamine and aggression, however
research has found a relationship between the two. There's some evidence to suggest that
increases in dopamine activity are associated in aggressive behaviour (Lavine). Similarly, the
use of dopamine antagonists (which helps to reduce dopamine activity in the brain), have been
used successfully as a way of reducing aggressive behaviour in violent delinquents (Buitelaar).
Recent research has, however, suggested that there's a slightly different role for dopamine in its
relationship with aggression. Dopamine is produced in response to rewarding stimuli such as food
and sex. Couppis et al have now found evidence that dopamine also plays an important
reinforcing role in aggression. This research suggests that some individuals intentionally seek
out aggressive encounters because of the rewarding sensations, caused by the increase in
dopamine, which these encounters provide.
Dopamine levels a consequence of aggression ­ Couppis and Kennedy (2008) found that in
mice dopamine levels will increase and act as a reward during an aggressive BUT effectively
"turning off" dopamine in the animal's brain also makes it more difficult for the animal to
move because of dopamine's important role in the coordination of movement but although

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Ferrari et al has found support for both the influence of both serotonin and dopamine in
aggressive behaviour. They allowed a rat to fight every 10 days at precisely the same time. On
the 11th day, the animal was not allowed to fight, but the researcher measured the levels of
serotonin and dopamine in its brain. They found that in anticipation of a pending fight, the
rat's dopamine levels had increased and serotonin levels decreased despite the fact that the
animal didn't actually fight.…read more

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Although cortisol alone isn't thought to increase aggression directly, Dabbs et al found that high
levels of cortisol inhibit testosterone and this in turn inhibits aggression. So by inhibiting
testosterone, cortisol can affect aggression levels because it increases anxiety and he
likelihood of social withdrawal. Studies have reported low levels of cortisol in habitual violent
offenders and in violent schoolchildren.…read more


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