Classic Evidence: Brain abnormalities in murderers

Classic Evidence, Raine et al: Methodology

  • Quasi-experiment
  • Matched pairs design
  • IV= NGRI
  • DV= brain differences
  • Participants
  • 41 murderers (39 men, 2 women)
  • all pleaded NGRI
  • Schizophrenics = 6
  • Head injury/ brain damage = 23
  • Drug abuse = 3
  • Affective disorder= 2
  • Epilepsy = 2
  • Hyperactivity/learning disability= 3
  • Personality disorder= 2
  • control group was formed by matching each murderer with a normal individual of the same sex and same age who had been tested using dentical PET imaging procedures in the same laboratory.
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The sample was obtained using opportunity sampling.  A PET scan was used to study the active brain. All participants were given an injection of a tracer (flurodeoxyglucose or FDG).This tracer is taken up by active areas of the brain and making it possible to compare the brains of the NGRI and control groups.  

1. Participants were given the chance to practice the CPT before receiving the FDG injection.

2. Thirty seconds before the FDG injection participants started the CPT so that the initial task novelty wouldn’t be FDG labelled.

3. Thirty two minutes after the FDG injection a PET scan was done of each participant. Ten horizontal slices of their brain wererecorded using the cortical peel and box techniques. The article provides precise details of the scanning techniques so that the study could be replicated.

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Brain Differences 

  • Reduced Activity- (reduced glucose metabolism) in some areas, notably the areas previously linked to violence.  
  • Abnormal Asymmetries – reduced activity on the left side of the brain, greater on the right.  This applied to some of the areas identified in the hypothesis as being linked to violence (the amygdala, thalamus and hippocampus).
  • No Differences in many brain structures, notably structures associated with mental illness but not violence.  

Other Differences Not Controlled For

  • Handedness: Six of the murderers were left handed but in fact they had less amygdala asymmetry and higher medial prefrontal activity than right handed murderers.
  • Ethnicity: 14 of the murderers were non-white but a comparison between them and white murderers showed no significant difference in brain activity.
  • Head Injury: 23 of the murderers had a history of head injury, but they didn’t differ from murderers with no history of brain injury.
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The study was carefully designed, involving a large sample and matched controls.  However, Raine et al acknowledge that head injury and IQ have not been ruled out as contributory factors.


  • The results do not show that violent behaviour is determined by biology alone; clearly, social, psychological, cultural, and situational factors also play important roles in predisposing to violence.
  • The results do not show murderers pleading NGRI are not responsible for their actions, nor do they demonstrate that PET can be used as a diagnostic techniques.
  • These findings do not establish a causal link between brain dysfunction and violence.   
  • Findings cannot be generalised at the present date from NGRI murder cases to other types of violent offenders. 

Nevertheless, the findings do suggest a link between brain dysfunction and a predisposition towards violence in this specific group of NGRI murderers, which should be further investigated.  

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Evaluation: Methodology and Procedures


The limitation of this method is that no casual conclusions can be drawn.  The danger is that readers misinterpret the findings and assume that criminal behaviour is predetermined and inescapable.    

The Research Technique 

PET scans enable the brain in action to be examined therefore allowing Raine et al to see how the brains of different individuals differed in the way they processed information.

The Sample

  • The murderers were not typical of all violent individuals which is acknowledged by Raine et al.  
  • The findings do not show that all violent offenders have such brain dysfunctions therefore the study can only draw conclusions.  
  • The crime is one of murder however many violent crimes do not involve murder therefore the conclusions are restricted to a particular group of people.  
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Ethical Issues

Valid Consent

  • The participants in this study were murderers who pleaded guilty by reason of insanity.  They may not have been mentally competent to provide valid consent.
  • The participants may not have fully understood what they would be required to do which could be deemed an example of psychological harm.  
  • They may NOT have fully understood their right to withdraw at any time, especially as they are prisoners.  

Socially Sensitive

  • The question is whether our understanding of criminal behaviour is advanced by this research.
  •  If the research indicates that murderers are born rather than made this may have consequences that would be disadvantageous for people with similar brain abnormalities.
  •  They might be imprisoned without trial or any reference to their social circumstances.  Therefore the research findings have implications for the prisoner.  


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Evaluation: Alternative Evidence

  • Yang and Raine (2009) was a meta-analysis of 43 imaging studies that considered both antisocial and violent behaviour.  The conclusion of this meta-analysis was that there is significantly reduced prefrontal activity in antisocial and/or violent individuals.
  •  These findings are supported by genetic studies that indicate a criminal gene.  An example of this is the MAOA gene (monoamine oxidase A) that causes abnormally high levels of the neurotransmitter dopamine.  
  • Tiihonen et al (2015) analysed the genes of 895 Finnish prisoners and found an association between this gene and an increased likelihood of committing a violent crime.
  •  Alternatively, James Fallon analysed his own genes and found that he had the genetic and brain characteristics of a violent criminal but he wasn’t one.  His positive experiences during childhood meant that his potentially criminal tendencies were not triggered (diathesis-stress explanation).
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