Vol. 5, No. 2, 1999 Page 1&3

PET scans show differences among murderers

When Adrian Raine and his colleagues viewed posi-tron emission tomography (PET) scans of 24 murderers, they detected an interesting pattern. Both predatory murderers and impulsive murderers had unusual PET scan results, but the two groups exhibited very d different types of brain abnormalities.

Raine et al. studied 15 predatory murderers, and 9 ‘affective’ murderers who committed impulsive crimes based on emotion. (All of the subjects had pleaded not guilty by reason of insanity, or incompetent to stand trial.) The murderers’ PET scans were comp pared to those of 41 control subjects with no evidence of medical or psychiatric disorders.

The researchers say that predatory murderers had excessive subcortical activity in the right hemisphere, but showed no significant abnormalities in prefrontal functioning. They note that subcortical dysfunction is linked to aggressive feelings and behavio or, while prefrontal activity is involved in logically planning and following through on a goal. Normal prefrontal activity in predatory murderers, Raine et al. say, “is consistent with the view that such offenders have relatively intact ability to plan and regulate their aggressive behavior in order to achieve desired goals.”

Affective murderers, by comparison, exhibited both lower prefrontal activity and higher right subcortical activity than controls. Reduced prefrontal functioning, the researchers say, may result in impulsiveness, loss of self-control, immaturity, poor emot tional control, and an inability to modify behavior.

The increased right-hemisphere subcortical activity in both groups of murderers is of interest, the researchers say, because subcortical abnormalities in the right hemisphere are linked to negative mood. Raine et al. speculate that excessive subcortical a activity contributes to an aggressive temperament in both types of murderers, but that “while predatory violent offenders have sufficient left prefrontal functioning to modulate such aggressive behavior in a way to bully and manipulate others to achieve d desired goals, affectively violent offenders lack this prefrontal modulatory control over their impulses, resulting in more unbridled, dysregulated, aggressive outbursts.”


“Reduced prefrontal and increased subcortical brain functioning assessed using positron emission tomography in predatory and affective murderers,” Adrian Raine, J. Reid Meloy, Susan Bihrle, Jackie Stoddard, Lori LaCasse, and Monte S. Buchsbaum, Behavio oral Sciences and the Law, Vol. 16, 1998, pp. 319-332. Address: Adrian Raine, Dept. of Psychology, S.G.M. Building, USC, Los Angeles, CA 90089-1061.

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