Affiliating with delinquent peers may stimulate the development of antisocial behavior, especially for adolescents who are sensitive to social rewards. The current study examines whether the association between delinquent peer affiliation (DPA) and disruptive behavior interacts with functional brain correlates of reward sensitivity in early onset male adolescents delinquents.

Childhood arrestees (n = 126, mean age = 17.7 [s.d. 1.6]) completed a DPA questionnaire, and participated in an fMRI study in which reward sensitivity was operationalized through responsiveness of the ventral striatum (VS), amygdala, and medial prefrontal cortex (mPFC) during the monetary incentive delay paradigm (reward anticipation and outcome). Symptoms of disruptive behavior disorders (DBD) were assessed through structured psychiatric interviews (Diagnostic Interview Schedule for Children) with adolescents.

DPA had a main effect on DBD symptoms. Adolescents with high VS reward responses showed a stronger significant positive association between DPA and DBD symptoms compared to low VS responders. No evidence for an interaction effect was found for the amygdala and mPFC. Post-hoc analyses revealed the positive association between DPA and DBD was only present in males, with a diminishing effect as age increased.

We found evidence for a biosocial interaction between DPA and reward sensitivity of the VS in relation to DBD symptom severity. This study provides the first evidence of an interaction effect between a brain mechanism and an environmental factor in relation to DBD symptoms, implying that susceptibility to influences of delinquent peers may intertwine with individual biological differences.

Prior research has indicated that affiliation with delinquent peers activates genetic influences on delinquency during adolescence. However, because other studies have indicated that the socializing effects of delinquent peers vary dramatically across childhood and adolescence, it is unclear whether delinquent peer affiliation (DPA) also moderates genetic influences on delinquency during childhood.

The current study sought to evaluate whether and how DPA moderated the etiology of delinquency in a sample of 726 child twins from the Michigan State University Twin Registry (MSUTR).

The results robustly supported etiological moderation of childhood delinquency by DPA. However, this effect was observed for shared environmental, rather than genetic, influences. Shared environmental influences on delinquency were found to be several-fold larger in those with higher levels of DPA as compared to those with lower levels. This pattern of results persisted even when controlling for the overlap between delinquency and DPA.

Our findings bolster prior work in suggesting that, during childhood, the association between DPA and delinquency is largely (although not solely) attributable to the effects of socialization as compared to selection. They also suggest that the process of etiological moderation is not specific to genetic influences. Latent environmental influences are also amenable to moderation by measured environmental factors.