In short, we anticipate that the internalizing pathway is not necessarily orthogonal to processes underlying the development of externalizing symptoms as related to SUDs. Rather, we expect that (a) independent contributions of internalizing and externalizing symptoms may only be evident outside of those developmental periods of high symptom co-occurrence (adolescence), (b) that the internalizing pathway may contribute to the ubiquity of externalizing symptoms during adolescence, with externalizing symptoms serving to mediate the relation between early emerging internalizing symptoms and subsequent SUDs, and (c) that the presence of externalizing symptoms may alter or moderate risk for progression along the internalizing pathway toward eventual Negative Affect SUDs. What distinguishes the internalizing pathway from the externalizing pathway is an emphasis on emotional dysregulation and the emergence of self-medication as the core features of the underlying disorder (i.e., Negative Affect SUDs). Thus, in the internalizing pathway, externalizing symptoms serve to propel or slow progression toward eventual Negative Affect SUDs, a specific form of SUDs with a unique psychological motivational structure and perhaps genetic liability.
