Insomnia longitudinally predicts reduced reward motivation in adults with elevated depressive symptoms

Sleep disturbance and reward dysfunction are both strongly associated with the onset and persistence of depressive disorders. Given this, examining their longitudinal associations within depression may provide important clinical insights. Existing research has not examined the relationship between sleep disturbance and reward dysfunction in depression over time, nor has it clarified the directionality of this relationship or the potential mediating or moderating role of sleep disturbance between depression and reward motivation. This study addresses these gaps by investigating these relationships among reward motivation, insomnia, and depressive symptoms in an adult population. The study included 101 community dwelling adults (M_age = 22.71, 69.31 % women, 54.46 % White) with varying levels of depression who completed six consecutive weekly assessments. During each assessment, participants completed the Effort Expenditure for Rewards Task, the Insomnia Severity Index, and the Quick Inventory of Depressive Symptomatology. Our results indicated that insomnia was significantly associated with reward motivation, and this association was moderated by expected value (the quantified outcome of a choice calculated by multiplying probability of reward and reward amount). Among those with higher prior-week depressive symptoms, prior-week insomnia predicted lower reward motivation the following week. Insomnia did not mediate or moderate the relationship between depression and reward motivation. Taken together, our findings suggest a unidirectional relationship between insomnia and reward motivation and underscore the importance of targeting sleep disturbances and mood symptoms in clinical interventions to improve reward functioning.