Neural and Hormonal Mechanisms in Aggression
Aggression in humans has been associated with low levels of serotonin and high levels of dopamine. Usually, serotonin has a calming effect, which inhibits aggression. When serotonin levels are low, this inhibitory effect is removed and people are less able to control their aggressive behaviour. Evidence for the importance of serotonin comes from two main sources. Brown (1982) found that there were low levels of the waste products of serotonin in the cerebrospinal fluid of individuals who are prone to impulsive and aggressive behaviour. The second source of evidence is studies where participants were given the drug dexfenfluramine, which reduces levels of serotonin in the brain. Mann (1990) administered dexfenfluramine to male and female participants, and found that males displayed more aggressive response on a questionnaire. A Meta analysis of 29 studies of serotonin and aggression showed that these studies consistently found evidence of low serotonin levels in antisocial children and adults. The levels of serotonin were particularly low in individuals who had attempted suicide, suggesting that low levels of serotonin lead to impulsive behaviour, one consequence of which is aggressive behaviour and, in some individuals, suicide. One of the consequences of low levels of serotonin is that the brain creates more receptors in an attempt to capture any serotonin that is available. This has been shown to be the case in research by Arora and Meltzer (2003), who found elevated levels of serotonin receptors in people who had committed violent suicide, thus supporting the claim that normal levels of serotonin have an inhibitory influence on violent behaviour. Ferrari (2003) showed support for serotonin in aggressive behaviour in an animal study for rats. They allowed rats to fight at the same time every day for 10 days, and not on the 11th day. They found that rats learned from their experience and had raised levels of...
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