Theory of Aggression: Brain Structure

Prefrontal Cortex

  • Part of the cerebral cortex, right at the front of the frontal lobe
  • Regulates behaviour and governs social interaction. It gives us the ability to delay gratification of an impulse by supressing messages from the amygdala

Evidence: The case study of Phineas Gage - Significant brain damage. He became less social and more rude due to destroying the frontal lobe and left side of the brain.

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Hypothalamus

  • Part of the limbic system
  • Maintains homeostasis (stability of the body) - regulates responses to emotional circumstances

Evidence: Animal experiments using cats (Flynn et al 1970) - Electrical stimulation of the hypothalamus in cats produces an aggressive response including hissing and growling

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Amygdala

  • Part of the limbic system
  • It is the centre of emotions, emotional behaviour and motivation
  • Stimulating produces an aggressive response

Evidence: The case study of Charles Whitman - spree killer who had a tumour adjacent to his amygdala (which may have been the cause)

Animal experiments using cats - Making lesions to the amygdala in cats produces aggressive behaviour. If the amygdala is stimulated using an electric current, then the animal displays aggression. If the amygdala is removed, then the animal becomes passive and unresponsive and does not show a fear response to stressors

Neuroimaging (Swantje et al) - 20 healthy volunteers in the normal range of lifetime aggression. Found a significant negative correlation between amygdala volumes and trait aggression. Volunteers with higher aggression scores had 16-18% smaller amygdala volumes 

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Evidence

  • Wide variety of evidence. PET (Raine) and MRI (Swantje) scans show adnormalities in brain activity and structure in aggressive individuals. Case studies and animal studies also suggest aggression may arise from structures in the brain
  • Brain scans only identify an association - doesn't mean it is the cause of aggression. Animal studies are difficult to generalise to humans. Similarly, difficult to generalise case studies to all humans and also unclear whether brain abnormalities are the cause of aggression
  • Conclusion: the breadth of evidence is compelling, but while abnormal brain structure and function may explain some cases of aggression, it may not be the only determinate of aggression
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Application

  • Raine: brain scans could be used to inform decisions about the appropriate sentencing and to help determine how appropriate it would be to offer parole to prisoners
  • Changes in level of aggression may indicate damage to specific parts of the brain (e.g tumour adjacent to Charles Whitman's amygdala) - may be helpful in diagnosis
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Strengths/Shortcomings

  • Scientific - techniques such as brain scans have scientific credibility and provide objective measures of brain activity. Studies are often well controlled and have good reliability
  • Determinist - suggests it is in the nature of some people to be aggressive and therefore, they have less free will. This is troubling because it suggests that they are less responsible for their aggression
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Alternative Theory

  • This theory is reductionist - A purely biological explanation seems to ignore important factors such as upbringing, culture and social expectation
  • Abnormal brain structure and functioning cannot explain all types of aggression (e.g premeditated murder , social aggression, legitimate aggression)
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