Neural and hormonal mechanisms in aggression

• Neural mechanisms in aggression - The limbic system

  Made of the:

  • Hypothalamus
  • Amygdala - How an organism assesses and responds to environmental threats and challenges + Predictor of aggressive behaviour
  • Parts of the hippocampus
  • Parts of the thalamus
• Neural mechanisms in aggression - The limbic system (Gospic et al)

  Ultimatum game - Two players where proposer splits money with responder deciding to accept or reject and end up with nothing

  Ppts were responders whiles brains were scanned by fMRI

  Findings:

  • Reject unfair offers - Fast and heightened response (Aggressive reaction to a social provocation)
  • Benzodiazepine drug (Reduce arousal of the autonomic nervous system) taken before - Halved number of rejections + Decreased activity of amygdala

  Conclusion: Evidence of association with reactive aggression and amygdala activity
• Neural mechanisms in aggression - Serotonin

  • Normal serotonin levels in orbitofrontal cortex - Linked with reduced firing of neurones + Associated with a greater degree of behavioural self-control
  • Decreased serotonin may disturb mechanism - Reduces self control and an increase in impulsive behaviour i.e. aggression
• Evaluation of neural mechanisms in aggression - Role of other brain structures

  • Studies indicate the amygdala does not operate by themselves
  • Functions in the tandem with the orbitofrontal cortex - Not part of the limbic system that is in self-control, impulse regulation
  • Coccaro et al: Psychiatric disorders with aggression - OFC activity reduced - Impulsive-control reduced

  Limitation: Need to take into account other mechanisms that play a part in aggression
• Evaluation of neural mechanisms in aggression - Effects of drugs on serotonin

  • Increase serotonin also reduce levels of aggressive behaviour

  Berman et al: Placebo or paroxetine (Enhances serotonin activity)

  Lab based game with electric shocks

  • Paroxetine ppts - Less and fewer intensive shocks than places - For ppts with a history of aggression
  • Evidence of a link with serotonin function and aggression

  Strength: Support validity and more evidence than correlational findings
• Hormonal mechanisms in aggression - Testosterone

  • Males are more aggressive than females
  • Testosterone - Regulates social behaviour
  • Animal studies - Experimental increases in T - Greater aggressive behaviour in several species

  Dolan et al: Positive correlation with T level and aggressive behaviours

  • History of personality disorders
  • Impulsively violent behaviour
• Evaluation of hormonal mechanisms in aggression - Other hormones

  • Mixed evidence

  Carre + mehta: Dual-hormone hypothesis

  • High level of T lead to aggression if cortisol levels are low
  • High cortisol levels - T influence on aggression is blocked

  Limitation: Alternative explanation that bring the theory into question