Brainwave studies implicate abnormalities of paralimbic system in psychopathic behavior

Psychopaths respond abnormally to threatening images, fearful facial expressions (see related articles in this issue), and emotional words and sounds, suggesting abnormalities in brain processes that underlie attention. A new study offers evidence that such abnormalities may stem from dysfunction of brain structures in the paralimbic system.

After testing 80 male maximum-security prisoners for psychopathic traits, Kent Kiehl and colleagues asked the prisoners to perform an auditory "oddball" task. The task involved responding to a target sound, while ignoring standard and random (oddball) non-target sounds. While the participants performed this task, the researchers recorded their brainwave responses.

Compared to non-psychopathic inmates, inmates whose test scores indicated psychopathy exhibited unusual brainwave patterns when detecting the target sound. (Abnormalities included a large, late N550, enlarged N2, and slightly decreased fronto-central P3.)

These abnormalities, the researchers say, are consistent with the "overfocusing" hypothesis of psychopathy, which suggests that psychopaths allocate so much attention to things of immediate interest that they effectively ignore other input. However, they say, their experiment showed that the psychopaths allocated more attention than non-psychopaths to processing both target and "oddball" tones.

A different explanation for the findings, Kiehl et al. say, is that they may reflect structural or functional abnormalities of the temporal lobe. They suggest that psychopathy may involve abnormalities of the paralimbic system, which includes the amygdala (strongly linked by other studies to psychopathy), the hippocampus, anterior superior temporal gyrus, cingulate cortex, and orbital frontal cortex (also previously implicated in psychopathy- See article, Crime Times, 1995, Vol. 1, No. 4, Page 6.

The researchers say brainwave abnormalities in their subjects resemble those of patients with temporal lobe damage. They also cite evidence that patients with temporal lobe epilepsy have a higher than average incidence of psychopathic behavior, and that "removal of the dysfunctional anterior temporal lobe in these epilepsy patients appears to reduce hostility, increase warmth and empathy in social relationships, and decrease inappropriate sexual behavior." In addition, they say, psychopaths show defects in processing emotional speech or faces that are similar to defects in patients with amygdala damage.