Describe and Evaluate Neural Mechanisms in Aggression

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Describe and evaluate neural mechanisms in aggression. (8 marks + 16 marks) Serotonin is a neurotransmitter that has an important role in social decision-making by inhibiting aggressive social responses. Serotonin usually reduces aggression by preventing stimulation of the amygdala, a structure in the brain's limbic system. Stimulation of the amygdala increases aggressive behaviour but serotonin prevents stimulation, thereby reducing aggression. If there are low levels of serotonin in the brain, there is less inhibition of the amygdala. As a result it becomes more active when stimulated by external events, 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. The relationship between low levels of serotonin and aggression has been supported by a study by Mann et al.. They administered the drug dexfenfluramine, which depletes levels of serotonin in the brain, to participants. The researchers then used a questionnaire to assess hostility and aggression levels, which were raised after taking dexfenfluramine in males but not in females. There may be a gender bias in this research. Although a link was found 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 female compared to males, and therefore there is a gender bias in human studies in this area. Further evidence comes from the use of drugs that raise levels of serotonin in the brain, such as antidepressants. In clinical studies, antidepressant drugs which elevate serotonin levels (e.g. SSRIs) also tend to reduce irritability and impulsive aggression. This suggests that increased serotonin levels do lead to reduced aggression.
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