As this was an initial attempt to understand the association between the EXT PGS, P3, and externalizing behaviors, we took a cross-sectional approach to maximize the sample size. In the future, longitudinal data will be used to determine the developmental trajectories of both P3 and externalizing behaviors and the impact of genetic liability on both these trajectories. These results suggest that P3 and the EXT PGS each index different facets of externalizing liability. The EXT PGS is formed from GWAS of substance use and risk-taking behaviors but did not include GWAS for antisocial or aggressive behavior as there were not samples available with sufficient power (all N < 50 000). Similarly, P3 amplitude is just one index of neurophysiological functioning that is relevant to externalizing psychopathology. Therefore additional, relevant electrophysiological phenotypes (e.g. Error Related Negativity, event-related oscillations) should be evaluated as potential brain-based responses that may partially account for the association between the EXT PGS and externalizing outcomes.
