Obviously, not all behaviorally inhibited infants will progress toward substance use and eventual disorder. Rather, we expect that progression involves the emergence of internalizing symptoms in the pre-school and early childhood years. Stable behavioral inhibition over time, particularly when paired with physiological indices of fear responses to novel stimuli, increases subsequent risk for internalizing symptoms (particularly anxiety, but also depression) in childhood (Gladstone & Parker, 2006; Hirshfeld, Rosenbaum, Biederman, & Bolduc, 1992; Kagan, Snidman, Zentner, & Peterson, 1999). Moreover, children of depressed parents show greater risk for early behavioral inhibition and internalizing symptoms (Rosenbaum et al., 2000). This same risk for greater internalizing symptoms is also seen in children of depressed (or Negative Affect) alcoholic parents versus children of alcoholic parents without depression and children of non-alcoholic parents (Hussong et al., 2008). Thus, we posit that the early stages of the internalizing pathway to SUDs are marked by behavioral inhibition and emerging internalizing symptoms from infancy into early childhood and we expect that children of parents with Negative Affect SUDs may be particularly vulnerable to this pathway.
