classic study: Raine et al. (1997) Flashcards
what was the aim of the study ?
they wanted to use brain scans to identify any brain impairments in murderers who had pleaded not guilty by insanity
what was their hypothesis ?
that the brain scans would show dysfunctions in areas linked in previous research to violence
what experimental design was used ?
matched pairs - 41 murderers and 41 non-murderers
what is the independent variable
whether they are a murderer or not
what is the dependent variable ?
the glucose metabolism (i.e activity) in specific brain areas
where was this experiment done ?
california
what were the murderers matched on ?
- age
- gender
- ethnicity
what screening processes did the control group undergo ?
- they had a physical examination
- they had a psychiatric interview
what are some other controls used on the control group ?
none were taking medication and none had a history of psychiatric illness - except the six who had schizophrenia which were matched on that characteristic
what type of brain scan was used ?
PETscan - injected with radioactive tracer so that brain activity would ‘light up’
explain the whole procedure ?
1) ppts injected with radioactive tracer
2) immediately after the injection the ppts did a continuous participation task (ppts had to identify targets on a screen) to increase uptake of radioactive tracer in areas of the brain that they wanted to investigate
3) they did the CPT for 32 minutes and then did the PETscan immediately after - the scan took 10 slices through the brain at 10mm intervals
what were the findings in the cortical regions ?
- murderers had a significantly lower glucose metabolism than the controls in areas such as the prefrontal areas, left angular gyrus and the left and right parietal areas
- murderers showed higher metabolism than the controls in the occipital lobe, a brain area not previously linked to violence
what the findings in the subcortical regions ?
- murderers had lower glucose metabolism than the controls in the corpus callosum, left amygdala and left medial temporal lobe (including hippocampus) (as supported in previous research)
- murderers had greater activity in the right amygdala, the right medial temporal lobe and the right thalamus (not previously implicated in violent behaviour)
what are the conclusions of the study ?
- the hypothesis was supported
- findings showed that murderers pleading NGRI have different brain activity from people who are not violent offenders
- murderers had impaired functioning in areas of the brain previously linked to violent behaviour