externalizing, understanding the role environmental factors play in the etiology of externalizing disorders is equally important. There is extensive evidence to suggest that environmental influences exert both direct and interactive effects on externalizing outcomes. For example, a large literature points to exposure to risky contexts (e.g., deviant peers) and stressful events (e.g., trauma) as powerful environments that interact with genes to confer risk for externalizing outcomes (e.g., Enoch, 2012; Hicks et al., 2004), including in studies of polygenic risk for externalizing (Sadeh et al., 2016; Salvatore et al., 2015). Based on these findings, incorporating the environment as a level of analysis in future polygenic-neuroimaging studies will be important for developing comprehensive etiological models of externalizing disorders.
