Researchers have used event-related potentials and electroencephalography (EEG) to investigate biomarkers for psychiatric disorders for decades (Iacono, 2018). The P3 (also termed the P300) is a positivity in the scalp electrical potential that occurs between 300–700 ms following a ‘significant’ rare stimulus or ‘target’. The P3 is typically measured at central parietal electrodes where it is maximum and in this context is thought to reflect an estimate of effortful, ‘top down’ attentional shift. Twin studies indicate that the P3 is highly heritable (estimates ranging from 0.49–0.78; Katsanis, Iacono, McGue, & Carlson, 1997; O’Connor, Morzorati, Christian, & Li, 1994; Van Beijsterveldt, Molenaar, De Geus, & Boomsma, 1996). Low P3 amplitude derived from a visual oddball task is a well-documented neurophysiological index associated with a broad liability for externalizing psychopathology in adults and late adolescence, including substance and alcohol use disorders, ADHD, and antisocial behavior (Euser et al., 2012; Porjesz et al., 2005). Twin studies of primarily White samples have shown that the association between P3 amplitude and externalizing behaviors are due, in part, to genetic correlation (i.e. shared genetic influences; 4.8%
