Psychopathy and antisocial personality disorder (ASPD) are both characterized by impulsive, externalizing behaviors. Researchers have argued, however, that psychopathy is distinguished from ASPD by the presence of interpersonal–affective features that reflect an underlying deficit in emotional sensitivity. No study to date has tested for differential relations of these disorders with the brain's natural orienting response to sudden aversive events.

Electroencephalography was used to assess cortical reactivity to abrupt noise probes presented during the viewing of pleasant, neutral and unpleasant pictures in 140 incarcerated males diagnosed using the Psychopathy Checklist – Revised and DSM-IV criteria for ASPD. The primary dependent measure was the P3 event-related potential response to the noise probes.

Psychopaths showed significantly smaller amplitude of P3 response to noise probes across trials of all types compared with non-psychopaths. Follow-up analyses revealed that this overall reduction was attributable specifically to the affective–interpersonal features of psychopathy. By contrast, no group difference in general amplitude of probe P3 was evident for ASPD versus non-ASPD participants.

The findings demonstrate a reduced cortical orienting response to abrupt aversive stimuli in participants exhibiting features of psychopathy that are distinct from ASPD. The specificity of the observed effect fits with the idea that these distinctive features of psychopathy reflect a deficit in defensive reactivity, or mobilization of the brain's defensive system, in the context of threat cues.