Describe and evaluate neural and hormonal mechanisms in aggression.

(8 marks + 16 marks) Plenty of AO1 and AO2 to choose from.

AO1 Serotonin

Serotonin plays an important role in social decision making by keeping aggressive social responses in check. Serotonin usually reduces aggression by inhibiting the firing of the amygdala, which might otherwise lead to impulsive or aggressive behaviour. If there are low levels of serotonin in the brain, there is less inhibition of the amygdala. As a result, when it is stimulated by external events, it becomes more active, causing the person to act on their impulses, and making aggression more likely. Therefore, low levels of serotonin have been associated with an increased susceptibility to impulsive and aggressive behaviour.


(Can be used for AO1 or AO2 you decide. )

Support from Brown et al who found that the major metabolite (waste product) of serotonin tends to be low in the cebrospinal fluid of people who display impulsive or aggressive behaviour.

AO2

The relationship between low levels of serotonin and aggression is supported by a study by Mann et al. (1990). They administered a drug (dexfenfluramine) to participants, which chemically depletes levels of serotonin in the brain. The researchers then used a questionnaire to assess hostility and aggression levels, which were raised after taking dexfenfluramine in males but not in females.

IDA

There may be a gender bias in this research. Although the Mann et al. study found a link between low levels of serotonin and aggression, this was not evident for the female participants. This suggests that the role of serotonin in aggression may be different for females compared to males and therefore there is a gender bias in human studies in this area.

AO1 Dopamine

The link between dopamine and aggressive behaviour is not as well established as the link between serotonin and aggression, however there is some evidence to suggest that increases in dopamine actively (ie via the use of amphetamines) are associated with increases in aggressive behaviour. Dopamine is produced in response to rewarding stimuli e.g. food, drugs etc. Couppis and Kennedy suggests that dopamine plays a role in reinforcing aggression. Couppis and Kennedy’s research suggests that individuals intentionally seek out aggressive encounters because of the rewarding sensations caused by the increase in dopamine, in which these encounters provide.

AO2

Ferrari et al provides research support for the influence of both serotonin and dopamine in aggressive behaviour. Ferrari et al allowed a rat to fight every day for 10 days at precisely the same time. On the 11^th days the animal was not allowed to fight but the researchers measured the levels of serotonin and dopamine in its brain. They found that the rat had an increased level of dopamine and decreased level of serotonin despite the fact the animal had not had a fight. This suggests a relationship with serotonin and dopamine in aggression.

The role of dopamine in aggression is also demonstrated in studies that have used amphetamines, which increase levels of dopamine. Lavine (1997) found that when participants were given amphetamines, there was a corresponding increase in their levels of aggression.

AO2/IDA

There is research that challenges this link. Scerbo and Raine (1993) carried out a meta-analysis of studies that had examined neurotransmitter levels in antisocial children and adults. They found lower levels of serotonin in those individuals described as ‘aggressive’ but no difference in dopamine levels for these individuals when compared to ‘normal’ individuals.

IDA

The link between neural mechanisms, such as serotonin and dopamine and aggression can be criticised as being reductionist. The complexity of human behaviour means that biological explanations are insufficient on their own to explain the many different aspects of human aggression. For example, Bandura found that children learned aggressive behaviour and imitated aggressive behaviour from models.

AO1 Testosterone

The male sex hormone testosterone is thought to increase levels of aggression from young adulthood onwards. It is thought that testosterone may influence areas of the brain that control behavioural reactions, such as the amygdala and the hypothalamus. Testosterone also influences the levels of other hormones which are thought to be involved in aggression, such as vasopressin.

AO2

There is research to support this from Dabbs et al who measured salivary testosterone in violent and non violent criminals. Those with the highest testosterone levels had a history of primarily violent crimes, where as those with the lowest levels had committed only non violent crimes. Studies of non prison populations have found similar trends. For example Lindman et al found that young males who behaved aggressively when drunk had higher testosterone levels than those who did not act aggressively.

AO2/IDA

However Mazur suggests that we should distinguish aggression from dominance. Individuals act aggressively when their intent is to inflict injury, where as they act dominantly if their wish is to achieve or maintain status over another. Mazur claims that aggression is just one form of dominance behaviour. In non human animals the influence of testosterone on dominance behaviour might be shown in aggressive behaviour. In human however, the influence of testosterone on dominance is likely to be expressed in more varied and subtle ways e.g. through status striving behaviour.