Yo,
Here's a summary:
Aims:
To show that the brains of
murderers who pleaded not guilty by reason of insanity were different from the
brains of non-murderers. Raine et al. Investigated whether brain dysfunction
predisposed people to violent behaviour.
Background Literature: Previous studies linked certain parts of the brain to violent
behaviour-
Ø EEGs, neurological and cognitive testing suggest that there is a link
between brain dysfunction and violent behaviour. The prefrontal cortex and
different functioning of the two hemispheres are thought to be important.
Ø Recent mapping techniques have found reduced electrical activity in the
left angular gyrus in violent offenders
Ø Some experimental animal research suggests that the limbic structures
(amygdala and hippocampus) and the thalamus are involved in aggression.
Raine listed these regions and studied them both in
murderers pleading not guilty by reason of insanity and in a control group. A
preliminary study of 22 murderers and 22 ‘normal’ participants gave some support
for prefrontal dysfunction in the murderers.
Procedure: There were 41
murderers pleading not guilty by reason of insanity and 41 controls.
There were 39 men and 2 women who had been charged
with either murder or manslaughter. Average age was 34.3. All had been referred
to the university of California Irvine Imaging Center to obtain evidence
relating to a ‘not guilty by reason of insanity’ defence or to gather evidence
for some other part of their trials to do with incompetence.
The group consisted of 23 people with a history of
brain damage, 6 schizophrenics, 3 people with a history of substance abuse, 2
had an affective disorder, 2 had epilepsy, 3 were diagnosed as hyperactive or
with a learning disability and 2 had paranoid personality disorder. None were
on medication.
The control group was formed by matching each murderer
with a normal participant of the same sex and age, and who was similar in other
ways, e.g. There were 6 schizophrenics. None of the control group was on medication.
The group consisted of 39 males and 2 females (average age 31.7).
PET scanning procedure: The procedure of the study was as follows..
Ø Each participant carried out a practice test
Ø 10 minutes later, a fluorodeoxyglucose (FDG) trace was injected
Ø The participant then completed a continuous performance task and target
recognition was recorded
Ø After a 32 minute period of FDG uptake, the participant was taken for a
PET scan of the head and images of slices of the brain were produced
Br
ain regions were identified by:
Ø The cortical peel technique- slices were examined and glucose values for
each region of interest were compared with those of other areas in a slice
Ø A box technique- 2cm2 boxes of brain area were examined and
linked scan results to the suggested areas for violence
Results: In the tasks
carried out before the PET scan there were no differences in performance
between the two groups.
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Cortical Regions
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Sub-cortical Regions
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Prefrontal lobe- the murderers had lower glucose
metabolism in comparison with controls in some areas
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Corpus callosum- murderers had lower glucose
metabolism than the control group
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Parietal lobe- the murderers had lower glucose
metabolism than the controls, particularly in the left angular gyrus and
bilateral superior parietal regions
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Amygdala- murderers had reduced activity in the left
amygdala and greater activity in the right amygdala than the controls
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Temporal lobe- no significant differences between
the groups
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Medial temporal lobe (including hippocampus)- murderers
had reduced left activity and greater right activity than controls
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Occipital lobe- Murderers had higher glucose
metabolism than controls
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Thalamus- murderers had greater right thalamic
activity than controls
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Raine et al. (1997) also looked at other variables
where the groups differed that may have affected results. They checked
right/left handedness and found that this would not have affected results. They
checked ethnicity and found no significant differences. They checked for head
injury, 23 murderers had history of head injury, this seemed to lower activity
in the corpus callosum.
Conclusions: It was concluded
that murderers pleading not guilty by reason of insanity have-
Ø Reduced glucose metabolism in the bilateral prefrontal cortex, the posterior
parietal cortex and the corpus callosum
Ø Abnormal activity in the amygdala, thalamus and medial temporal gyrus,
including the hippocampus
These findings support the idea that violence has
biological causes.
Ø Prefrontal deficits can result in impulsivity and loss of self-control,
as well as emotionality and an inability to modify behaviour
Ø Limbic deficits show the amygdala is associated with aggressive
behaviour, both in animals and humans. The amygdala, hippocampus and prefrontal
cortex govern the expression of emotion and the thalamus relays information.
The hippocampus is thought to modulate aggression (in cats) and there is other
evidence linking the limbic system to aggression, emotion and control
Ø The posterior parietal cortex seems to be linked to cognitive
functioning. For example, reductions in glucose metabolism in the left angular
gyrus have been correlated with reduced verbal activity. Cognitive dysfunction
could mean educational and occupational failure, which may lead to crime and
violence
Ø A dysfunction in the corpus callosum may explain hemisphere differences
because the corpus callosum links the two hemispheres. The right hemisphere has
been said to generate negative effects in humans and may be in the murderers
less regulated by the right hemisphere. Studies of rats reinforce this idea.
Findings show that neural processes underlying
violence are complex and that there is no single mechanism in the brain that
causes violence. ‘Violent behaviour probably involves disruption of a network
of multiple interacting brain mechanisms that predispose violence in the
presence of other social, environmental and psychological predispositions’.
Overall, murderers pleading guilty by reason of
insanity seem to have different brain functioning from controls.
KOP!
