In edexcel as/a level biological psychology, we look at the classical study of Raine et al. (1997) who wanted to see whether there was different brain functioning in a group of murderers compared to a control group of participants. This document also contains the contemporary study of Li et al. (20...
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3.3 Studies
Classic study
3.3.1 Raine et al. (1997) Brain abnormalities in murderers indicated by positron
emission tomography.
aim?
to see whether there was different brain functioning in a group of murderers
compared to a control group of participants
Hypothesis?
the murderers would show evidence of brain differences in their prefrontal
cortex as well as in other areas that are thought to be linked to violent
behaviour
Suggestions of expectations from previous research
Violent offenders had poorer brain functioning
Damage to the prefrontal cortex was linked to aggression
Abnormal function of the hemispheres in violent offenders
Possible dysfunction to the corpus collosum in violent offenders
The limbic structures (amygdala and hippocampus) are linked to
aggression
independent variable?
Whether the participant is an offender pleading Not Guilty by Reason of
Insanity (NGRI) to murder, or a non-murderer in the Control group.
Since the IV is naturally-varying and the Controls were matched on age and
sex, this is a natural experiment with what looks like matched pairs design.
However, Raine didn't pair each participant's results up with their "opposite
number" in the other group, so really this is independent groups design.
3.3 Studies 1
, dependent variable?
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).
sample?
41 offenders pleading NGRI to the crime of murder and 41 Controls. The NGRIs
were 39 men and 2 women (mean age 34.3); 23 had a history of brain
damage, 3 with a history of drug abuse, 6 suffered from schizophrenia, 2 with
epilepsy and 7 with other emotional or learning disorders. The Controls were
people of the same age and sex with no history of crime or mental illness,
except 6 Controls who had schizophrenia.
The NGRIs should be considered an opportunity sample; Raine does not
describe how the Control group was recruited so that may be considered to be
an opportunity sample too.
procedure?
The participants were tested at the University of California. Each was injected
with the glucose tracer and then performed the Continuous Performance Task
(CPT) for 32 minutes. Then the PET scan was carried out. Raine used other
experimental controls:The participants were allowed to practice the CPT ten
minutes before the glucose tracer was injected to make sure they were all
equally familiar with it. Raine made sure none of the participants (NGRIs or
Controls) was on medication; the NGRIs had been kept medication-free for 2
weeks before the PET scan.
results?
The PET scan was broken down into digital "slices" and "boxes", enabling
Raine to measure the relative amount of tracer present in the brain's 4 cortical
regions (the "lobes" on the outside of the brain) and the 4 sub-cortical regions
(structures tucked away deeper inside the brain).As expected, the NGRIs
showed less activity in the frontal lobe, especially the prefrontal cortex which
is associated with rational thinking, self-restraint and memory.There was also
less activity in the parietal lobe, which is associated with abstract thinking
(such as "morality" or "justice" but more activity in the occipital lobe (vision).In
the sub-cortical region, the NGRIs had less activity in the corpus callosum: the
3.3 Studies 2
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