amygdala and aggression

• Amygdala


  Processes information from our senses and determines how we respond to that information
• Amygdala


  • Can trigger the flight or fight response when we either run away from the situation or stay and fight
  • When it is activated the amygdala overrides the rational part of our brain so we are less likely to think in a rational manner
• Damage to the amygdala

  Can lead to an individual being unable to prevent themselves acting spontaneously in an aggressive way
• Amygdala


  • Part of the limbic system, located deep within the temporal lobe in both hemispheres
  • Directs how we react to threatening situations and also responsible for controlling human emotions
• Abnormalities in the size, structure and activity of the amygdala


  Correlate with increased aggression, making criminal behaviour more likely
• Damage to the amygdala

  Can lead to less control over aggressive impulses, therefore making someone more aggressive
• Dustin Pardini et al (2014) study


  • Neuroimaging scans on a group of 26 year old men
  • Men divided based on normal vs reduced amygdala volume
  • Latter group (smaller amygdala) were 3 times more likely to be aggressive, violent and show psychopathic traits than the others
  • Suggests amygdala size can predict future violence
• Adrian Raine study

  Reduced metabolic activity observed in several brain areas of psychopathic murderers, including the left amygdala
• Raine et al (1990) study


  • Investigated a fear response in 1795 3-year-olds
  • Children who had gone on to commit crime were more likely to be those who had failed to exhibit a fear response
  • Explained by abnormal functioning of the amygdala, illustrated by the lack of fear at age 3
• A weakness of research into the amygdala is that other brain areas are implicated
• OFC (Orbitofrontal Cortex)

  • Part of the frontal lobe and not the limbic system
  • Thought to regulate self-control and its reduced functioning is associated with increased aggression and violent outbursts
  • Suggests the influence of the amygdala (and all brain areas) on aggression (and crime) is difficult to disentangle
• Phineas Gage


  • American railroad construction foreman
  • At age 25, an iron rod penetrated his left cheek, travelled behind his left eye, entered through his left side brain, and exited his skull
  • After the accident, Gage's personality was said to have changed as a result of the damage to the frontal lobe of his brain
  • Injury led to a loss of social inhibition, meaning Gage would behave in ways that were considered inappropriate
• Damasio (1994) study


  • Built a 3D computer representation of Gage's skull to map out how the iron rod passed through the brain
  • Damage was likely only to the frontal lobe, no other brain areas were harmed
  • The iron rod went through the left eye socket and up through the head
  • Damage to white matter and neurons meant Gage was unable to pass neural messages in this part of the brain, making it useless
• 12 other patients with frontal lobe damage also lost emotional control
• Brower and Price (2001) study


  Literature review of documented brain injuries revealed many case studies show antisocial personality can arise after frontal lobe injury
• Sham Rage

  • Emotional state found in animals where neural connections to the cortex were severed, leading to rage and aggression behaviours
  • Source of the rage came from the temporal region, specifically the amygdala
  • When the amygdala was ablated, the animals became much more placid; if the area was stimulated, aggression would be displayed
• Sham rage studies conducted on animals can be largely criticised for lacking generalisability to humans
• Narabayashi et al (1963) study


  Conducted psychosurgery on human patients with aggressive behaviour by severing their amygdala from the remaining limbic system and found a mood-stabilising effect in the majority of patients over time
• Brain structure cannot be the only factor that makes psychopaths who they are, or the structural abnormalities that lead to psychopathy do not necessarily lead to aggression and criminality