While the present study’s focus was on the relationship between P3-related activity and externalizing disorders, an important next step in the characterization of these components as endophenotypes is to investigate their heritability and association with familial risk for externalizing disorders. P3 amplitude has been shown to be strongly heritable (van Beijsterveldt & van Baal, 2002; Yoon, Iacono, Malone, & McGue, 2006), and the relationship between P3 and externalizing can be accounted for by shared genetic effects (Hicks et al., 2007). Future studies will utilize our large twin sample to extend these findings to the TF-PCA derived components associated with the P3 ERP. Given that topographic differences may also play a role in the relationship between P3, TF components, and externalizing (e.g. theta contributions to P3 tend to be frontally maximal, while delta contributions tend to be parietally maximal; (e.g. Basar-Eroglu et al., 1992; Jones et al., 2006)), future work will assess a broader range of electrode sites to capture any topographically-mediated variance.
