Neural and hormonal mechanisms

• NEURAL MECHANISMS : The Limbic System – The Amygdala

  • Perez (1937) and Maclean (1952) linked the limbic system to aggression. The limbic system is a network of structures buried deep inside the brain
  • The amygdala is the most important structure associated with aggression. The amygdala plays a key role in humans and animals in how they assess and respond to environmental threats and challenges
• Neural - limbic system - amyglada

  • The reactivity of the amygdala in humans has proven to be an important predictor of aggressive behaviour
  • Research has shown that there is a clear association between reactive aggression and amygdala activity
• Neural - The Limbic System – Ultimatum Game

  • Gospic et al. (2011) used a well-established laboratory method of assessing aggressive behaviour called the ‘Ultimatum Game’
  • This game involves two players. One player proposes to split money in a certain way and the other player either rejects (aggressive act) or accepts this offer
  • Participants had their brains scanned with fMRI while playing
• Neural - limbic system - ultimatum game

  • Researchers found that when one player rejected an offer (aggressive reaction) the scan showed a fast and heightened response by the amygdala
  • They also found that benzodiazepine drugs decreased the activity of the amygdala and reduced aggression – this shows that there is an association between aggression and amygdala activity
• Neural - serotonin:

  • Serotonin is an inhibitory neurotransmitter
  • This means it slows down and dampens the activity of neurons 
  • Normal levels of serotonin in orbitofrontal cortex are linked with reduced firing of neurons, which is associated with a greater degree of self-control 
  • Serotonin also stops the firing of the amygdala, which controls fear, anger and other emotional responses
• Neural - serotonin:

  • Decreased serotonin leads to reduced self-control, leading to an increase in impulsive behaviour such as aggression
  • Virkkunen et al. (1994) found that there were lower levels of a serotonin breakdown product in the cerebrospinal fluid of violent impulsive offenders compared to violent non-impulsive offenders
  • This suggests that low serotonin levels are linked to impulsive aggression behaviour
• Hormonal - testosterone:

  • Males are generally more aggressive than females
  • Males have more of the hormone testosterone which is responsible for the development of masculine features
  • Animal studies have demonstrated experimental increases in testosterone are related to greater aggressive behaviours in several species 
  • Dolan et al. (2001) found a positive correlation between testosterone levels and aggressive behaviours in a sample of 60 male offenders in UK maximum security hospitals. These men had histories of violent impulsive behaviour
• AO3:

  • limitation - The limbic system's explanation of aggression oversimplifies aggressive behavior
  • Recent research suggests the amygdala and orbitofrontal cortex (OFC) work together in determining aggression.
  • coccaro found Patients with psychiatric disorders featuring aggression show reduced activity in the OFC.
  • This suggests that aggression is complex and involves more than just the limbic system and amygdala.
• AO3:

  • Strength of link Between Low Serotonin and Aggression is that drugs increasing serotonin activity also reduce levels of aggressive behaviour
  • Berman et al. (2009) study found a link between low serotonin and aggression.
  • Participants given either a placebo or Paroxetine, which increased serotonin activity.
  • Participants gave fewer and less intense electric shocks with Paroxetine.
  • Research supports the link between serotonin function and aggression.
  • Experiment goes beyond correlational findings, proving the validity of the serotonin explanation of aggression.
• AO3:

  • Research support - by Mehta and Josephs (2006) supports the link between increased testosterone levels and aggression.
  • They found that 73% of losers with higher testosterone challenged their opponents after a competitive game, while only 22% of those with lower testosterone challenged. - This suggests that increased testosterone levels during daily events, such as competition, can lead to more aggressive behavior.
• AO3:

  • A limitation of explaining aggression only in terms of testosterone is that other hormones may also be involved 
  • Carre and Mehta (2011) propose the dual-hormone hypothesis, claiming that high levels of testosterone lead to aggressive behaviour only when cortisol levels are low
  • When cortisol is high, testosterone’s influence on aggression is blocked
  • This suggests that the combined activity of testosterone and cortisol may be a better predictor of human aggression than just testosterone alone.
• AO3:

  • limitation of research into both neural and hormonal influences on aggression is that much of this research is correlational
  • This is because it would be unethical to manipulate brain structures and hormones in humans 
  • However, when two variables are correlated (e.g. Testosterone and aggression) it is impossible to establish which one is the cause of the other, or if a third variable is involved
  • Therefore, research showing a correlation between two variables (e.g. Testosterone/serotonin and aggression) risks oversimplifying the true mechanisms involved in aggression