Neural mechanisms

• What are neural mechanisms?

  • Research on non-humans has delivered a consensus that aggression is not in separate brain functions but rather in an interaction of systems. 
  • In the brain, there is a collection of many networks called the limbic system which is made up of many different structures like the hypothalamus, amygdala and hippocampus. 
• What is the prefrontal cortex?

  • Research shows that the most important structure is the amygdala, which helps organisms assess and respond to environmental threats.
  • Over activity of the amygdala in humans is an important predictor of aggressive behaviour.
• What is prefrontal cortex?

  • The prefrontal cortex is also important as a neural mechanism as it controls the outward expression of aggression.
  • It is involved in planning and moderating behaviour.
  • It acts as a mediator of the emotional control from the amygdala and deciding whether it should act on them. 
  • Damage to the prefrontal cortex can result in loss of control, impulsivity, immaturity and altered emotional state, which are linked with aggression - Damasio et al (1994) 
• What is serotonin?

  •  It has inhibitory effects on the brain where normal levels are associated with good self-control as it inhibits the firing of amygdala, causing less acting on the impulse of the amygdala.
  • People with low levels can control their aggressive impulses less.
  • When the amygdala is affected by the environment, it becomes active causing more impulses, causing more aggression.
  • This leads to an increase in impulsive behaviour and aggression.
  • This is known as the serotonin deficiency hypothesis. 
• Psychosurgery supporting evaluation?

  • Supporting evidence comes from psychosurgery.
  • Narabayashi et al (1972) reported that 43 out of 51 patients who had their amygdala removed, showed more social behaviour with reduced aggression.
  • This shows the amygdala is involved in aggression.
• Case study supporting study?

  • Charles Whitman supports the role of the amygdala - he was a student at the university of Texas.
  • In the early hours of August 1st 1996, he murdered his wife and mother in their homes.
  • Later on, he brought guns and started firing on top of a clock tower in the university, injuring 32 people and killing 14 people.
  • He was shot but left a suicide requesting that his body be done for an autopsy to investigate his headaches and his actions.
  • He had a tumour pressing on his amygdala, which neurologists speculate had some effect on his violent acts.
• Prefrontal cortex supporting evaluation?

  • Neuroimaging studies found reductions in prefrontal brain tissue in people with antisocial and aggressive tendencies.
  • Particular aggressive individuals have impaired functioning in the prefrontal cortex.
  • Raine et al looked at 41 murderers using PET scans.
  • PET scans work by taking up glucose when certain brain areas are working. The more taken up, the more active that brain area is.
  • He found that there was reduced glucose metabolism in the prefrontal cortex.
  • This suggests that damage to the prefrontal cortex may lead to more aggression.
• Serotonin supporting study?

  • Duke et al (2013) - A meta analysis of 175 studies with 6500 p’s.
  • They found a negative correlation between serotonin and aggression.
  • The lower the serotonin levels, the higher the aggression.
  • The strength also depended on the type of report method used to measure aggression.
  • Self-report gave different results to other people reporting the aggression. The role of serotonin lacks validity.  
• Deterministic?

  • People with damage to the PFC or the amygdala will experience impulsive aggression.
  • There is no free will due to biological determination.
  • It is socially sensitive as to whether people with damage to their brain are responsible for their acts.
  • If they have a faulty brain circuit that affects their moral reasoning, should they be held responsible for their criminal behaviour?
  • This would have great implications on the criminal justice system as if this would affect the severity of sentencing.
  • It has limits due to correlation and case studies.
• Reductionist?

  • It reduces aggression to the functioning of brain structures and focuses on nature.
  • It has been found that situational factors and social learning are also important in aggression.
  • Therefore a diathesis stress model of biological vulnerability and an environmental trigger is more likely