neural and hormonal mechanisms

• What is included in the limbic system


  amygdala, hippocampus, hypothalamus
• What is the amygdala's role?

  key role in how an animal responds to environmental challenges - important predictor of aggressive behaviour
• What if the amygdala malfunctions?

  can be due to tumour, damage or atypical development - level of testosterone raised making aggressive behaviour more likely
• What is the hippocampus' role?

  Involved in forming long term memories - allow to compare conditions of current threat with similar past experiences
• What if the hippocampus is impaired?

  prevents the nervous system from putting threats into context so amygdala may respond inappropriately resulting in aggressive behaviour
• LIMBIC EVALUATION - support from Groves and Schlesinger

  amygdalectomy - found it reduces aggression in previously violent individuals - side effect is loss of emotion - amygdala involved in processing emotions like anger
• LIMBIC EVALUATION - support from Raine et al

  MRI scans on unsuccessful psychopaths (caught) revealed hippocampus differed in size in either hemisphere unlike successful psychopaths (not caught) - concluded asymmetry may impair ability of amygdala and hippocampus to work together leading to impulsive aggression in unsuccessful psychopaths - memory processed in hippocampus influences aggressive behaviour
• describe serotonin 


  has a widespread inhibitory effect throughout brain
• normal levels of serotonin 


  inhibits firing of amygdala - controlling fear, anger
• low levels of serotonin - serotonin deficiency hypothesis

  remove inhibitory effect - consequence of individuals aren't able to control impulsive aggressive behaviour
• SEROTONIN EVALUATION - support from Raleigh et al

  vervet monkeys fed high diet of tryptophan (increases serotonin levels) showed decrease in aggression - monkeys fed low tryptophan diet showed increase in aggression - difference in aggression could be due to serotonin level
• SEROTONIN EVALUATION - support from Bond

  found antidepressant drugs that raise serotonin levels tend to reduce impulsive aggression - serotonin may have direct impact on aggression
• SEROTONIN EVALUATION - support from Scerbo and Raine

  meta analysis of 29 studies - found there were consistently lower levels of serotonin in highly aggressive children and adults as well as people who had attempted suicide - low serotonin leads to impulsive and aggressive behaviour
• androgen group of hormones (testosterone - hormonal)

  male sex hormones - testosterone - aggression generally higher in males than females
• what is testosterone associated with

  development of masculine features (body hair) - action on brain areas controlling aggression
• Basal model of testosterone


  testosterone causes a change in a level of dominance - more testosterone = more competitive and dominant - man with high level of testosterone will take part in anti social behaviour like fighting to express dominance
• testosterone in women


  levels higher in men - studies shown a positive relationship between testosterone and aggression in women - more influenced by smaller changes in levels than men
• dual hormone hypothesis


  testosterones role in status relevant behaviour should depend on concentrations of cortisol (hormone released in response to physical and psychological stress)
• TESTOSTERONE EVALUATION - support from Dabbs

  measured testosterone in saliva of criminals - found highest levels had history of primarily violent crimes - lowest levels had committed only non violent crimes - suggests testosterone may have caused this difference
• TESTOSTERONE EVALUATION - gender bias

  most studies focus on males and have ignored possibly different influence testosterone may have on females - eisenegger found testosterone could make women nicer rather than aggressive depending on the situation - testosterone promotes status seeking behaviours that increase dominance, aggression is only one type