Reward responsivity and habit formation in the co-occurrence of restrictive eating and nonsuicidal self-injury.

Dysfunctions in reward and/or habit formation have been proposed as factors contributing individually to the maintenance of restrictive eating and nonsuicidal self-injury (NSSI). However, despite the high comorbidity between these behaviors, the associations between reward and habit formation in their co-occurrence remains unclear. This study examined self-reported reward responsivity and habit strength among individuals with co-occurring restrictive eating and NSSI (Comorbid group; n = 108) and those with one behavior only (One-behavior group; n = 113). Hierarchical logistic regression analyses assessed the association between reward and habit features and the co-occurrence of restrictive eating and NSSI, accounting for the effects of impulsivity (a characteristic commonly considered to underlie co-occurring disordered eating and NSSI). Partial correlations examined the relationships between these features and the severity of eating disorder and NSSI symptoms, also controlling for impulsivity. Lower reward responsivity was associated with the co-occurrence of restrictive eating and NSSI, even after accounting for impulsivity (p = 0.017). In exploratory analyses, this relationship was no longer significant after accounting for self-reported depression. No significant associations were found regarding habit formation and restrictive eating and NSSI co-occurrence. Lower reward responsivity was linked to increased NSSI frequency and versatility in both groups and associated with severity of eating pathology in the Comorbid group (ps < 0.05). Our findings suggest that blunted reward responsivity may relate to the co-occurrence of restrictive eating, NSSI, and depressive symptoms, as well as the severity of restrictive eating and NSSI. Reward disturbances may serve as a crucial target in the treatment of multiple self-destructive behaviors.