Classic study: Raine et al (1997) Brain abnormalities in murderers as indicated by PET
: Raine et al (1997)
Brain abnormalities in murderers as indicated by PET
Participants tested at University of California, where each was injected with the glucose tracer
Performed a Continuous Performance Task (CPT) for 32 minutes, then the PET scan was carried out
Participants were allowed to practice CPT ten minutes before the glucose tracer was injected so they were familiar with it
Raine made sure none of the participants (NGRI's or controls) had medication, NGRI's were kept medication-free for 2 weeks before PET scan
PET scan broken into digital 'slices' for Raine to measure the relative amount of tracer present in the brain's 4 cortical regions (lobes on outside of the brain) and 4 sub-cortical regions (structures tucked away inside the brain)
Large sample of 41, largest at the time, anomalies that disputed the test by not focusing on CPT shouldn't skew the data too much -> representative results of a wider population
PET is reliable, used since the 1970's producing objective and replicable results and can be retested to check for reliability
CPT ensures participants were concentrating on the same, which ensures they all had similar types of brain activity, standardised procedure that adds to reliability
NGRI's are unusual offenders, people who have killed someone but either don't remember doing it or are too confused to stand trial, so aren't representative of "typical" murderers
To see if there is a difference in structure of brain activity between people who have committed murder (NGRI's) and non-murderers.
NGRI's showed less activity in frontal lobe, especially prefrontal cortex which associates with rational thinking, self-restraint and memory
Less activity in parietal lobe associated with abstract thinking (morality or justice), but more activity in occipital lobe (vision)
NGRI's had less activity in corpus callosum and imbalance of activity between left and right hemispheres in limbic system
Whether the participant is an offender pleading Not Guilty by Reason of Insanity to murder, or a non-murderer in the Control group.
Natural experiment with matched pairs design, but Raine didn't pair each participant's results up with their "opposite number " in the other group, so this is independent groups design.
Relative glucose levels in the prefrontal cortex, the other lobes of the brain, the corpus callosum, the amygdala, the MTL/hippocampus and thalamus, as revealed by Positron Emission Tomography (PET).
41 offenders pleading NGRI to the crime of murder and 41 controls
NGRI's were 39 men and 2 women (mean age 34.3); 23 with history of brain damage, 3 with a history of drug abuse, 6 schizophrenics ,
Prefrontal lack of activity might make someone more impulsive
Lack of activity in limbic system might make someone aggressive; amygdala controls urges and desires, thalamus processes information and the hippocampus processes memory
Lack of activity in corpus callosum make it harder for the brain's hemispheres to communicate
Areas like amygdala and hippocampus play a part in recognition; lack of activity here might make it harder for someone to judge social situations