Raine et al Flashcards
aims
-To identify Brain impairments in people charged with murder who pleaded NGRI (not guilty by reasons of insanity)
-Specifically there would be dysfunctions in areas of the brain linked to aggression like the prefrontal cortex, amygdala, hippocampus, thalamus, corpus callosum, angular gyrus.
Procedure
-matched pairs design
-IV = murderers and non-murderes
-DV= glucose metabolism (activity) in specific Brain areas
Sample:
-39 men and 2 women, people charged with murder pleading NGRI (free from all medication in the two weeks up to brain scan, urine test)
-Murdered matched with controls on sex, age and ethnicity. (no medication or history of psychiatric illness apart from six controls with schizophrenia, matched on this characteristic).
-Participants did a continuous performance test (identifying targets on a screen for 32 minutes) and were injected with a radioactive tracer during the task so that at the end, a PET scan could detect the active areas of the brain.
-The scan took ten images (slices) through the brain at 10mm intervals
Findings
Cortical regions
-Less activity in murderers than control in : lateral/medial prefrontal areas, left angular gyrus, left/right superior parietal areas.
-Murderers: Higher metabolism in occipital lobe (no prior link to violence
Subcortical regions
-lower glucose metabolism in murderers than controls in: corpus callossum, left amygdala, left medial temporal lobe and hippocampus
-Murderers : greater activity in the right amygdala, right medial temporal lobe, right thalamus (no prior link to violence).
Conclusions
The hypothesis was supported - murderers pleading NGRI had different brain activity from controls, with impaired functioning in brain areas earlier identified as involved with violent behaviour.
Dysfunctions of a single Brian area cannot explain violent behaviour, and not in a simplistic cause-and-effect manner.
The most likely explanation is that networks of interacting brain areas are functionally impaired, creating predisposition to violence that is only expressed in behaviour when social environment and psychological conditions are ‘right’.
Need caution in interpreting the findings because there were other brain areas involved in aggression that were not scanned.
A strength of the study is that it had a high degree of experimental control.
-For example, ppts were matched across the experimental and control on three potentially cofounding variables
-Standardised procedures were also used to control other variables e.g. the same CPT was used with all participants for 32 minutes, and PET scans followed a protocol so the procedure was identical for all ppts.
-This means the study has high internal validity as potentially cofounding variables were controlled and differences in experience of the procedure could not explain the results.
Competing argument
However a key element was not controlled because the participants were not randomly allocated to the two groups (matching was used to partly overcome this but it was not thorough).
Failure to match on some variables may have confounded some of the results. For example, Raine et al acknowledged that a history of head injury (in 23 murderers) may have explained the differenced in corpus callous activity between the two groups.
A weakness is that the PET technique may have given misleading results
Brains were scanned in 10mm slices relative to the canthomeatal line, an imaginary line from the outer corner (canthus) of the eye to the middle of the ear.
The line varies greatly between individuals which makes tit hard to locate precisely the different brain areas under study
This reduces the internal validity of the study and casts some doubt on the accuracy of the findings
Application: we should be cautious about biological evidence
This study appears to suggest that certain aggression-causing brain structures can be identified, so aggression can be ‘treated’ by changing biological structured through medication or surgery
However, Raine et al take great pains to argue that their findings do not show that such treatment is justified (because Brain structures offer only a partial explanation).
therefore, this research is important in identifying what biological evidence does and does not tell us.
