The present study examined how inter-trial phase-locking on target trials relates to externalizing disorders and tested the hypothesis that reduced inter-trial phase-locking contributes to the association between reduced P3-related evoked energy and externalizing psychopathology. Energy and phase-locking scores in delta and theta frequencies corresponding to P3 peak-latency were smaller for externalizing-diagnosed individuals in comparison to controls. To the best of our knowledge, this is the first report demonstrating that reduced phase-locking was a significant predictor of antisocial behavior, CDDs, and SUDs. Additionally, by using both evoked energy and inter-trial phase-locking in the same model to predict externalizing diagnoses (rather than evoked energy by itself), we accounted for more variance in externalizing diagnoses. In some cases (e.g., frontal delta) this improvement in fit was small whereas in others (e.g., theta), it was larger (see Table 2). Moreover, theta-band associations between evoked energy and externalizing composites (Any-SUD and Any-EXT) were significantly mediated by theta phase-locking. This was not the case for delta-band evoked energy and phase-locking.
