Neural and Hormonal Mechanisms

• Neural : Limbic System


  Amygdala:

  • Responsible for quickly evaluating emotional importance of sensory information and responding appropriately
  • The more responsive the amygdala, the more aggressive a person is
  • In animals, stimulation of certain areas means a aggressive response.

  Kulver and Bucy - destruction of amygdala in dominant monkey caused them to lose their status in social group
• Neural : Limbic System


  Hippocampus:

  • Involved in formation of LTM to compare current with past experiences
  • Impaired function may cause amygdala to respond inappropriately

  Boccardi et al - violent offenders exhibited abnormal hippocampal functioning
• Neural : Serotonin


  Typically inhibits the function of the amygdala meaning normal levels in the OFC reduces firing of neurons.

  Low serotonin:

  • Inhibitory effect removed
  • Amygdala becomes more active
  • Aggressive response is likely

  Mann et al gave 35 healthy people a drug to reduce serotonin and found an increase in aggression in males.
• Hormonal : testosterone


  Produces male characteristics and is thought to be linked to aggressive behaviour.

  • Males are generally more aggressive
  • Males are more aggressive to other males when testosterone levels are high (21-35) (Daly and Wilson)
  • Animal castration studies showed that aggression levels in mice decreased after castration (Wagner et al)
  • Studies of prison populations showed that those with high testosterone had a history of violent crimes (Dabbs et al)
• Hormonal : Progesterone


  Some evidence that progesterone plays a role in aggressive behaviour in women.

  • Progesterone levels are lowest during and just after menstruation.
  • Ziomkiewicz et al found low levels = increased aggression
• Eval : Strength


  Rosado et al compared aggressive dogs and non-aggressive dogs, and found there was significantly lower levels of serotonin in the aggressive dogs. Provides research support for neural mechanisms.
• Eval : Strength


  Dolan et al found a positive correlation between testosterone levels and aggressive behaviour in a sample of 60 male offenders in maximum security hospitals. Provides research support for hormonal mechanisms.
• Eval : Weakness


  Albert et al found no correlation between testosterone levels and violent behaviour among prison inmates suggesting that the explanation suffers from biological reductionism.