Impulse control problems of differing types, including child and adult antisocial behavior and abuse of alcohol and other drugs, exhibit high rates of comorbidity in the population, leading to suggestions that these disorders may be etiologically related (for early proposals of this sort, see: Achenbach & Edelbrock, 1978; Jessor & Jessor, 1977). Recently, researchers have documented an underlying dimension of proneness toward disorders of this type, labeled “externalizing,” that is associated also with personality traits of impulsivity, aggression, and sensation seeking (Krueger, 1999; Krueger, McGue, & Iacono, 2001; Krueger et al., 2002). Variation in general proneness to externalizing problems and traits has been shown to be highly heritable (>80%; Krueger et al., 2002). From this standpoint, the dimension of externalizing proneness represents an important target for neurobiological research on psychopathology, and studies have begun to examine brain-processing deviations associated with variations in externalizing proneness. These studies have demonstrated inverse relationships between levels of externalizing tendencies and amplitude of two brain event-related potential (ERP) components: the error-related negativity, or ERN (a negative polarity response that occurs following performance errors on speeded
