Psychology - Aggression Neural and Hormonal mechanisms

• there are 2 types of aggression. Proactive aggression is cold blooded and a planned method to get what you want.

  Reactive aggression is hot blooded and based on impulse
• The limbic system is a system of structures in the brain that includes the amygdala, hippocampus, and hypothalamus. It helps to coordinate behaviours that satisfy emotional urges. The limbic system plays a key role is how organisms reply to environmental threats.
• The hypothalamus is responsible for regulating the autonomic nervous system which also helps to regulate responses to emotional circumstances. Damage can result in aggression.
• The Amygdala is responsible for attaching emotional significance to sensory memory. Reactivity of the amygdala is an important predictor of aggression - more responsive amygdala = more aggressive person
• In the limbic system signals are passed from the lower systems to the higher systems in the prefrontal cortex. Here, feelings are monitored and interpreted which then helps to trigger a physical response. Damage would reduce the inhibition of the amygdala causing more aggression.
• The hippocampus is involved in the formation of long term memories and allows animals to compare current threat with past experiences. Damage may cause the amygdala to respond inappropriately to sensory stimuli leading to aggression
• What was the main aim of the GOSPIC study?

  To investigate the role of the amygdala in reactive aggression
• What was the procedure used in the GOSPIC study?

  • Lab study involving 2 players: proposer and responder
  • Proposer offers to split money (fair or unfair)
  • Responder can accept (money split) or reject (both get nothing)
  • Responders underwent fMRI scans during the game
• What was observed in the fMRI scans when responders rejected offers?


  There was a heightened response by the amygdala
• How did the administration of benzodiazepine affect the game outcomes?


  It halved the number of rejections and decreased amygdala activity
• What conclusion can be drawn from the GOSPIC study regarding reactive aggression?

  There is an association between reactive aggression and amygdala activity
• What roles do the proposer and responder play in the Ultimatum game?

  • Proposer: Offers to split money
  • Responder: Decides to accept or reject the offer
• Boccardi et al: Hippocampus research

  F: habitually violent offenders exhibited abnormalities of hippocampla functioning

  C: provides evidence of role of hippocampus in aggression
• Serotonin is a neurotransmitter that has inhibitory effects in the amygdala. normal levels of serotonin in the orbitofrontal cortex leads to reduced firing of neurons which leads to better self control. Decreased seretonin removes the inhibitory effect and reduces self control leading to aggression. when the amygdala is then stimulated it becomes more active.
• Virkunnen et al - serotonin

  P: compared serotonin levels breakdown product in cerebrospinal fluid of violent impulse and violent non-impulsive offenders.

  F: levels significantly lower in impulsive offenders
• Mann et al - effects of drugs on serotonin

  some drugs can alter serotonin levels and increase aggression.

  P: gave 35 healthy patients a drug known to reduce serotonin levels. used a questionnaire to assess aggression levels.

  F: use of drugs in males led to increased aggression.
• limitation of Amygdala studies - other brain structures may be involved.

  more recent research suggests non-limbic structures also involved in aggression. Orbitofrontal cortex not part of limbic system but involved in impulse regulation and inhibition of aggression.

  COCCARO et al:

  F: OFC activity reduced in disorders involving aggression. reduced activity disrupts OFC impulse control.

  C: neural regulation of aggression more complex than amygdala theories suggest.
• Testosterone is an androgen which produces male characterisitics like aggression. levels of this hormone peak in young males and then begin to decline. Testosterone has a role in regulating social behaviour via its influence on certain brain areas associated with aggression.
• Carre and Olmstead

  testosterone levels are not fixed they can fluctuate due to changes in the environment. changes in testosterone influence aggressive behaviour by increasing amygdala reactivity as a result of social threat.
• Dabbs et al

  P: measured salivary testosterone in violent and non-violent criminals.

  F: those with high testosterone had history of violent crimes.
• AO3: Dual hormone hypothesis.

  conflicting evidence on link between testosterone and aggression.

  Carre and Mehta

  high levels of testosterone lead to aggression only when accompanied with low levels of cortisol.

  when cortisol is high testosterone's influence is blocked.

  activity of testosterone and cortisol together may be better predictor af aggression
• AO3: inconsistent evidence

  some studies fail to find relationship between testosterone and aggression.

  Albert found a positive correlation between testosterone levels and self

  reported levels of aggression in prison inmates.

  but no correlation between testosterone levels and actual violent behaviour. suggests relationship is unclear.