biological: aggression

• Limbic system


  Responsible for emotions, forming memories and aggressive behaviour
• Amygdala


  Responds to threatening stimuli with a fight/flight response, important in reactive aggression
• Hypothalamus


  Regulates physical experiences like hunger, thirst and temperature, and regulates behavioural responses to things like pain, threats and sexual satisfaction by controlling hormonal levels including testosterone
• Homeostasis


  The process that maintains stability of the human body in response to external conditions e.g. temperature
• Amygdala


  Enables instinctive reactions to the environment with emotions such as happiness, anxiety and anger, connects to the pre-frontal cortex which may lead to the expression of aggression
• When exposed to threatening stimuli


  The amygdala is activated, resulting in increased emotional arousal and the fight or flight response
• The amygdala itself doesn't actually produce aggression, it is connected to other parts of the brain that produce aggression, but it is necessary to initiate the aggression</b>
• Impulsive/reactive aggression


  Aggression shown in direct response to a provocative stimulus with little planning
• Prefrontal cortex


  Involved in planning, problem solving, social judgement, decision making and the regulation of emotional responses
• Prefrontal cortex


  Allows us to control reactive aggressive impulses that stem from the amygdala, inhibiting us from automatically reacting to threats and allowing us to think about an appropriate course of action
• Serotonin


  Neurotransmitter involved in regulating mood, anger, aggression, sleep, arousal and appetite, low levels associated with increased impulsive and reactive aggression
• Low serotonin levels in the prefrontal cortex

  Results in less inhibition of the fight/flight response of the amygdala, increasing the likelihood of reactive, impulsive aggression
• Not Guilty by Reason of Insanity (NGRI) plea is a legal defense where the defendant is caught but claims not guilty due to mental health issues at the time of the crime
• Raine et al's study was the largest sample of violent offenders assessed using functional brain imaging at the time
• As the brain uses glucose as energy, the areas of the brain which are most active absorb it
• The radioactive material with it is picked up by the scanner
• The scanner produces coloured images of the level of activity occurring throughout the brain
• Positron Emission Tomography (PET)


  A technique that uses a scanner to produce coloured images of the level of activity occurring throughout the brain
• Participants


  • 41 people (39 Ms and 2 Fs) in the experimental group
  • 41 people (39 Ms and 2 Fs) in the control group
• Experimental group


  • Criminals with convictions for murder or manslaughter who were being tested to gain evidence to support a claim of NGRI
  • 6 had schizophrenia
  • 23 had suffered organic brain damage or head injury
  • 3 were substance abusers
  • 2 had an affective disorder
  • 2 had epilepsy
  • 3 suffered with hyperactivity and/or learning disability
  • 2 were diagnosed with passive-aggressive/paranoid personality disorder
• Control group


  • Matched to the experimental group on age, gender and psychiatric illnesses such as schizophrenia
  • Screened for general health, which included a physical examination, access to their medical history and a psychiatric interview
  • Excluded if they had a history of seizures, head trauma or substance misuse
• Consent was obtained from all participants before the PET scan was administered
• Procedure


  1. Participants completed a continuous performance task (CPT) as a practice trial 10 minutes before being injected with fluourodeoxyglucose (FDG)

  2. After a further 32 minutes on the CPT a PET scan was then completed to measure the metabolic rate in different areas of the brain in order to look at activity levels in those areas
• Results


  • The NGRI group showed lower activity in the prefrontal cortex, lower activity in parietal areas, higher activity in the occipital lobe, identical activity in the temporal lobe, lower activity in the corpus callosum, asymmetrical activity in the amygdala and medial temporal lobe, and higher level activity in the right of the thalamus
• These brain differences have been associated with many behavioural changes that could be related to violent behaviour
• Dysfunction in the prefrontal cortex has been linked to impulsivity, lack of self-control and an inability to learn from the consequences of behaviour
• The hippocampus, amygdala and thalamus have all been related to learning and it has been suggested that abnormal activity here could result in criminals being unable to modify their own behaviour by learning from the consequences of their actions
• The sample used in the research was the largest sample of severely violent offenders to be studied in this way and compared to matched controls
• An effort was made to eradicate possible effects of medication on brain activity by keeping participants drug-free for two weeks before the scan
• The findings cannot be used as an explanation for other types of violent behaviour or indeed criminal behaviour as a whole
• The use of a PET scan provides reliable comparisons to be made between the groups as all participants were subject to the same procedure
• There could be a number of possible extraneous variables that could interfere with these findings, such as social or situational factors that may contribute to either violent behaviour, brain dysfunction, or both
• The researchers were cautious about the findings and stated that additional research would need to be conducted to be sure that the patterns of brain dysfunction were related to violent behaviour
• Males are more aggressive than females on average
• Testosterone


  Male sex hormone that is thought to increase levels of aggression from young adulthood onwards
• Testosterone levels drop off in older men
• Gender is an issue in psychology when research exaggerates differences between men and women (alpha-bias) or minimises them when differences do exist (beta-bias)
• Focusing on testosterone as a major cause of aggression may characterise men as superior because of physical strength, dominance and violence and women as weaker and inferior
• All males are not violent and women are capable of violence
• Reductionism is a problem as testosterone is not the only biological variable at play in aggressive behaviour