Classic Raine et al. (1997) Flashcards
Aim
Investigate whether murderers have dysfunctions in areas of the brain linked in previous research to violence.
Hypothesis
Brain scans would show dysfunctions in areas linked in previous research to violence - prefrontal cortex, angular gyrus, amygdala, hippocampus, thalamus and corpus callosum.
Method
Looking at differences between 41 murderers and 41 non-murderers.
Matched pairs design.
Procedure - Sample
39 men and 2 women charged with murder but pleaded NGRI.
- Free from all medication in 2 weeks leading up to brain scan.
- Matched by sex, age and ethnicity with a non-murderer control group.
- 6 control patients had a diagnosis of SZ.
Procedure - Study
- PET scan, injected with radioactive tracer to light up brain metabolism on scanner.
- Continuous performance task - identifying targets on a screen and pressing a button during a 32 minute period after injection.
- PET scan conducted immediately after 32 min period and it took 10 images at 10mm intervals.
Findings In Cortical Regions
Murderers had significantly lower glucose metabolism than controls in lateral and medial prefrontal areas, left angular gyrus and left/right parietal areas.
Murderers - Higher metabolism than controls in occipital lobe, not previously linked to violence
Findings in Subcortical Regions
Murderers - Lower glucose metabolism than controls in corpus callosum, left amygdala, and left medial temporal lobe.
Murderers - Greater activity in right amygdala, r medial temporal lobe and r thalamus.
Conclusions
Hypothesis supported.
- NGRI murderers have different brain activity from non-violent offenders.
- NGRI had impaired functioning in areas of the brain previously identified with violent behaviour.
What did Researchers conclude?
- Dysfunctions of a single brain area cannot explain violent behaviour, and not in a simplistic cause-effect manner.
Most likely expl is that networks of interacting brain areas are functionally impaired which create predisposition to violence that is only expressed in behaviour when the conditions are right.
What did Raine conclude?
Be cautious of interpreting the findings as other brain areas are known to be involved in violence that they could not scan.
Cannot fully explain neurophysiology of violence.
Valuable as provides useful preliminary evidence and signposts several directions for future research.
Strength
High degree of control.
PP’s were matched across the experimental and control groups on three potentially confounding variables.
Standardised procedures used to control other variables (same CPT for all PP’s for 32 mins).
PET scans followed same well established protocol so experience was the same for all.
High internal validity and potentially confounding variables were controlled
Competing
PP’s were not randomly allocated to experimental or control group. The matching used was not thorough, failure to match on some variable could have confounded some results.
Raine acknowledged the head injuries in some PP’s may have explained difference in corpus callosum activity between groups.
Weakness
PET scanning technique may have given misleading results.
Scanned brain in 10mm slices relative to the canthomeatal line. This line is known to vary significantly between people making it hard to locate different brain areas.
Reducing internal validity as it casts doubt on accuracy of findings.
Applicability
To be cautious of bio evidence.
Research suggests that some brain structures can be identified to cause aggression, therefore it can be treated with medication or surgery.
Raine et al argues their findings do not show that such treatment would be justified as brain structure offers only a partial explanation.
This research important in underlying what bio evidence does and doesn’t tell us.
