Neuropsychological Studies

Neuropsychological studies have shown impaired decision making strategies and other indications of executive dysfunction in impulsive subjects. Neurocogni-tive measures of impulsive decision-making have shown robust deficits in antisocial subjects, supporting the relevance of impulsivity in the study of antisociality. Antisocial substance abusers favored immediate monetary rewards over larger delayed monetary rewards (discounting of delayed rewards) faster than substance abusers without significant antisocial psychopathology. Both groups discounted delayed rewards at a greater rate than controls and discounting of delayed rewards correlated with a trait measure of impulsivity (Petry, 2002). Similar findings were demonstrated when comparing psychopathic subjects, defined by the Psychopathy Checklist-Revised—PCL-R (Hare, 1991), to incarcerated controls on the gambling task (Bechara et al, 1994), another measure of risk vs. reward decision making (Mitchell et al, 2002), which has been associated with orbital-frontal function (Bechara et al, 1994). Moreover, additional studies have replicated the finding that antisocial subjects favor larger immediate rewards despite long term losses (Van Honk et al, 2002; Mazas et al, 2000).

There are also robust findings of decreased performance in other areas of executive functions associated with impulsivity. Pathological gamblers demonstrated higher order attentional impairment and may have elevated rates of childhood ADHD (Rugle & Melamed, 1993). Adolescents without conduct problems showed a significant task condition effect on P300 event-related potentials and left prefrontal activation, suggesting greater brain activity with the harder task. This task effect was reduced or absent in subjects with conduct problems, suggesting difficulty mobilizing the frontal resources in the performance of executive functions (Bauer, Hesselbrock, 2001). In another study, (Barratt et al 1997) assessed executive function in a group of impulsive-aggressive felons compared to those who exhibited non-impulsive aggression. All subjects met DSM-III-R criteria for anti-social personality disorder. Impulsive-aggressive felons showed lower verbal symbol decoding and peak P300 amplitudes relative to non-impulsive aggressive felons. Moreover, impulsiveness and verbal skills were inversely correlated. This study highlights how impulsivity and antisociality, although frequently comorbid, are nonetheless dissociable.

The findings are somewhat less consistent regarding executive dysfunction in explicitly antisocial groups. The lack of consistency in this area may be due to the heterogeneity in antisocial samples, such that executive dysfunction relates most to impulsivity but not antisociality per se (i.e., antisocial attitudes vs. behavior) (Morgan, Lillienfeld, 2000). Nonetheless, in a meta-analytic study of 39 reports of executive dysfunction in psychopaths, psychopaths demonstrated a difference of .62 standard deviations below controls (Morgan, Lillienfeld, 2000) but the authors note that inconsistent definitions of antisociality, e.g., confounding antisociality with criminality, complicates interpretation of the finding. Likewise, a study of violent offenders compared with normal and marginally mentally retarded controls, showed deficits in attentional set-shifting but not spatial or figurative working memory or planning (Bergvall et al, 2001). However, in another study, centro-frontal event-related potentials (N350) were stronger in psychopaths vs. nonpsychopaths during three verbal tasks, suggesting abnormal frontal processing of verbal tasks. Moreover, psychopaths showed more difficulty identifying abstract words (Kiehl, Hare et al, 1999).

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