P300 amplitude, externalizing psychopathology, and earlier- versus later-onset substance-use disorder

P300 amplitude predicts substance use or disorder by age 21. Earlier- versus later-onset substance disorders may reflect different levels of an externalizing psychopathology dimension. P300 in adolescence may not be as strongly related to later-onset substance problems as it is to earlier-onset ones. In the present study, visual P300 amplitude was measured at age 17 in a community-representative sample of young men. Substance and externalizing disorders were assessed at approximately ages 17, 20, and 24. Earlier-onset (by age 20) substance disorder was associated with higher rates of externalizing disorders than were later-onset problems. P300 amplitude was reduced in subjects with earlier-onset substance disorders, relative to later-onset and disorder-free subjects. Amplitude was also reduced in subjects with an externalizing disorder but no substance disorder. Earlier-onset subjects had reduced P300, even in the absence of an externalizing disorder. The results could not be attributed to a concurrent disorder or to recent substance use at the time of the P300 recording. The findings are consistent with P300 indexing an externalizing spectrum. Earlier-onset substance disorders are more strongly related to P300 and externalizing than are later-onset problems.