neural mechanisms

• neural mechanisms = brain structures
• research on animal s suggests that aggression is dependant on the interaction of a system of structures in the brain
• 3 neural influences which are important in aggression 


  1. Amygdala (part of limbic systems)
  2. Pre-fontal cortex (PFC)
  3. serotonin
• Amygdala

  1 on each side of brain

  positioned within the temporal lobes

  they are part of the limbic system

  has a key role in how we asses & respond to threats and challenges in our environment

  over activity/sensitivity of the amygdalae has proven to be an important predictor of aggressive behaviour
• pre-frontal cortex 


  located in the frontal lobes

  involved in planning and moderating our behaviour

  directly connected to limbic system

  regulates the amygdala-driven emotional responses and forms emotional control

  -takes impulses from amygdala and decides whether to act on them
• damage to PFC


  means that the amygdala is not regulated which results in loss of control, impulsivity, immaturity and altered emotions = all are associated with aggressive behaviour
• serotonin 


  normal levels = calming effect on neuronal firing in the brain

  serotonin inhibits the firing of electrical activity in the amygdala - high level of self control

  but low levels = removes this inhibitory effect , so less able to control their aggressive impulses - increasing impulsive behaviour = including aggression

  = serotonin deficiency hypothesis
• support for role of amygdala 


  evidence supporting comes from psychosurgery

  Narabayshi - reported that 43 out of 51 patients who had operations to destroy their amygdala showed more normal social behaviour after (reduced aggression)

  = suggests that amygdala was involved in producing the aggression
• support for role of amygdala

  Charles Whitman, student at university of Texas

  he murdered his wife and mother in their homes in the morning and later on went on a shooting rampage - killing 14 people , wounded 32

  he was shot and killed at the scene by police

  he left a suicide note requesting an autopsy - to find an explanation for his recent actions and headaches

  • was found that he had a tumour pressing on his amygdala and that his may have contributed to his violent acts
• support for role of PFC


  neuroimaging studied often find reductions in PF brain tissue in aggressive people - also having impaired functioning of the PFC

  study example - Raine , investigated brain activity of 41 murderers using PET scans (assessing brain activity by measuring glucose uptake by brain cells) the more glucose they uptake the more active they are

  • found reduced glucose metabolism in the PFC = suggest damage to PFC can lead to increased aggression
• support for role of serotonin 


  evidence - Duke et al - conducted a meta analysis of 175 studies involving 6500 p's.

  found negative correlation between serotonin levels and aggression

  the lower the serotonin levels - the more aggressive they were

  • but they found that the strength of the relationship varied depending on the method used to asses aggression - self report gave different results to other people reporting the aggression = lacks validity
• general criticism

  reductionist

  reduced aggression to the functioning of brain structures

  focuses on nature & ignore nurture

  • situational factors like the social learning theory (imitating models) and situational factors are likely to be important for aggression
  • aggression is likely to be due to a combination of biological vulnerability and environmental trigger = diathesis- stress)
• general criticism

  deterministic

  suggests people with damage to amygdala & PFC will be violent and cant control their aggressive urges - but some people have damage and aren't aggressive

  suggests there's no free will , biological determination of behaviour

  = social sensitive , have to ask if people with brain damage are responsible for their violent acts