|Vol. 5, No. 4, 1999 Page 3|
Two new studies, both using event-related potentials (ERPs), report that criminal psychopaths and teenagers with conduct disorder have abnormal responses to stimuli.
Kent Kiehl and colleagues studied a particular brainwave response, known as the P300, in 11 psychopathic and 10 non-psychopathic prison inmates. (Psychopaths, who are characterized by egocentricity, shallowness, manipulativeness, deceitfulness, selfishne ess, and lack of empathy, remorse, or guilt, are generally more dangerous and far less responsive to rehabilitation efforts than other prisoners.)
The researchers measured subjects’ response to a visual “oddball” task, in which the participants responded to a low-probability visual stimulus. The P300 response to an “oddball” task, Kiehl et al. say, “is thought to be sensitive to changes in the alloc cation of attentional resources and processes involved in contextual updating and decision making.”
The researchers report that among non-psychopathic subjects, the amplitude of the P300 was larger when target stimuli appeared than when other stimuli appeared. “In contrast,” they say, “psychopaths failed to show reliable P300 amplitude differences betwe een the target and non-target conditions,” and exhibited a smaller amplitude P300 in response to target stimuli than did other subjects. In addition, the psychopaths’ P300 response was less lateralized, which the researchers say is interesting in light of f f evidence indicating that psychopathy is associated with weak or abnormal lateralization of the cerebral hemispheres.
The researchers also found that the psychopaths exhibited an abnormal late centro-frontal negative wave (N550) when target stimuli were presented. This is the first study to identify this abnormality among psychopaths doing a task that did not require lin nguistic processing.
Overall, the researchers say, their findings suggest that “psychopaths are abnormal in their ability to mobilize and rapidly focus attention to stimuli to which they are required to respond. Once focused, it may be extremely difficult for them to remobili ize and switch attentional resources.”
Noting that a family history of alcohol or drug dependency did not have a significant effect on P300 amplitude, the researchers suggest that P300 decrements associated with substance abuse by other studies may in fact be related to undiagnosed conduct dis sorder.
“Reduced P300 responses in criminal psychopaths during a visual oddball task,” Kent A. Kiehl, Robert D. Hare, Peter F. Liddle, and John J. McDonald, Biological Psychiatry, Vol. 45, 1999, pp. 1498-1507. Address: Robert D. Hare, 2136 West Mall l, Department of Psychology, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada.
“P300 decrements in teenagers with conduct problems: implications for substance abuse risk and brain development,” Lance O. Bauer and Victor M. Hesselbrock, Biological Psychiatry, Vol.46, 1999, pp. 263-272. Address: Lance Bauer, Department o of Psychiatry MC 2103, University of Connecticut Health Center, Farmington, CT 06030.