Gender constitutes another unresolved issue related to P3AR as a developmental endophenotype. The most robust evidence supporting P3AR as an endophenotype is from findings involving male subjects. Although P3AR has been observed in high risk girls (Hill, Muka, Steinhauer, & Locke, 1995), P3AR in females is less well studied and the evidence is not as strong. Because the P300 response is not a unitary phenomenon, and reflects instead multiple electrophysiological processes overlapping in potentially complicated (and perhaps sex-specific) ways, studies using techniques that permit more precise characterization of the ERP, such as time-frequency methods (cf. Gilmore, Malone, Bernat, & Iacono, 2009; Makeig, et al., 2004), may prove fruitful in helping to bridge the gender gap in our understanding of endophenotypes involving brain activity. In addition, considering the role of gender might lead researchers to modify their conceptualizations of externalizing. For instance, self-harm behavior, which is more common among female adolescents than males, clearly represents a form of disinhibited behavior. Borderline personality disorder also shares key features with externalizing. Indeed, P3AR has been observed among adolescents with borderline personality (Houston, Bauer,
