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MURDERERS' BRAINS: PET OFFERS INSIGHTS
In 1995, Adrian Raine and colleagues reported the first results of
their positron emission tomography (PET) studies of the brains of
murderers found not guilty by reason of insanity
(see related article, Crime Times, Vol. 1, No. 1/2, Pages 1&6).
Comparing 22 murderers to 22 carefully matched
control subjects, the researchers found that the murderers had much
lower levels of glucose uptake in the prefrontal cortex.
Raine et al. have now expanded their study to include 41 murderers
(39 men and 2 women), matched with 41 control subjects. "To our
knowledge," they say, "this is the largest sample of violent offenders
assessed on functional brain imaging." The researchers controlled for
handedness, age, sex, ethnicity, and presence or absence of head
injury. In addition, the six schizophrenic murderers were matched with
six schizophrenic control subjects.
Again, the group of murderers showed reduced glucose metabolism in
the prefrontal cortex. "Damage to this brain region," Raine et al.
note, "can result in impulsivity, loss of self-control, immaturity,
altered emotionality, and the inability to modify behavior, which can
all in turn facilitate aggressive acts." Other abnormalities seen in
the murderers included reduced glucose metabolism in the superior
parietal gyrus, left angular gyrus, and the corpus callosum, and
abnormal asymmetries of activity in the amygdala, thalamus, and medial
temporal lobe. Defects of these brain areas, the researchers say, also
have been linked to violence or to cognitive defects associated with
criminality.
These results, the researchers say, "provide initial indications of a
network of abnormal cortical and subcortical brain processes that may
predispose to violence in murderers pleading not guilty by reason of
insanity." The researchers do not believe the various mental disorders
of the murderers distorted their findings, because, they say,
"differences in brain functioning in murderers show a different pattern
to that observed in other mental disorders." And although prefrontal
dysfunction may be common to many mental disorders, Raine et al. say,
the abnormalities they found in other brain areas "may lead to a
pathway toward violence as opposed to other conditions."
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"Brain abnormalities in murderers indicated by positron emission
tomography," Adrian Raine, Monte Buchsbaum, and Lori LaCasse,
Biological Psychiatry, Vol. 42, 1997, pp. 495-508. Address: Adrian
Raine, Dept. of Psychology, S.G.M. Bldg., University of Southern
California, Los Angeles, CA 90089-1061.
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