The present results demonstrated that activity indexed by the P3 can be more optimally represented by multiple overlapping TF components. Further, these components accounted for externalizing-related variance including and beyond what is indexed by P3. These findings suggest that these TF measures may be more sensitive to variance related to these disorders, and contributes to the growing suggestion that TF representations of EEG/ERP may produce more optimal indices of underlying neurophysiological processes. Specifically, the measured delta activity during the early stages and peak of P3 (i.e. PC3) was the most sensitive index. Given findings of links between delta (and theta) and genes related to alcoholism and externalizing spectrum disorders (Dick et al., 2008; Porjesz et al., 2005), this delta activity may serve as a more parsimonious endophenotype for externalizing psychopathology than P3-AR itself.
