neural mechanisms

• The limbic system is a group of subcortical structures in the brain which is thought to regulate emotional behaviour such as aggression
•  Papez and McClean identified the amygdala as the most important part of the limbic system in terms of aggression.
• The amygdala has a key role in humans and non-human animals how they assess and respond to environmental threats and challenges. The reactivity of the amygdala is an important predictor of aggressive behaviour.
• Serotonin, which is a neurotransmitter, is thought to reduce aggression by inhibiting responses to emotional stimuli that might otherwise lead to an aggressive response.
• Normal levels of serotonin in the orbitofrontal cortex are linked with a reduced firing of neurons, and is associated with greater self-control (less-likely to engage in aggressive behaviour).
• Low levels of serotonin have been linked with an increased susceptibility to impulsive behaviour, aggression and even violent suicide
• Gospic devised a lab-based study (the ultimatum game), to investigate the role of the amygdala in reactive aggression. The proposer offers to split money in a certain way with a responder. If the responder accepts the offer the money is split as proposed. But if the responder rejects the offer, neither gets the money. Researchers scanned responders in the game using fMRI to highlight areas of the brain. They found that when responders rejected unfair offers (an aggressive response) scans revealed heightened activity in the amygdala.
• They also found that if responders were given benzodiazepines prior to the ultimatum game it halved the number of rejections and reduced activity in the amygdala.
• Research suggests the amygdala does not function alone but with the orbitofrontal cortex (not part of the limbic system). Emil Coccaro et al (2007) found that patients with psychiatric disorders involving aggression had reduced activity in the OFC.
• Mann et al (1990) gave 35 subjects a drug called dexfenfluramine, which reduces serotonin levels in the brain to find out if it would lead to increased aggressive behaviour. They used a questionnaire to assess hostility and aggression levels, and found an increase in hostility and aggression scores in males.

  • this study has methodological issues (sample and self-report technique)