Motivation to expend physical and cognitive effort as predictors of functioning in major depression
Background: Major Depressive Disorder (MDD) is associated with severe functional disability; however, the mechanisms of impaired functioning are understudied. Cognitive deficits is one known mechanism of functional impairment in MDD. However, treatments that remediate cognitive functioning do not seem to produce commensurate gains in day-to-day functioning. Current models of functioning in MDD do not take into account motivation deficits that characterize the mood disorder. MDD individuals have demonstrated avoidance behavior and impaired performance in physically- and cognitively- effortful tasks, despite the promise of large rewards. Motivation to expend effort has yet to be evaluated as a predictor of functioning in depression. Objectives: This study aimed to compare physical and cognitive effort expenditure for rewards and the factors that influence motivation to expend high levels of these types of effort in MDD relative to healthy comparison individuals. Secondary objectives were to examine whether motivation to expend physical and cognitive effort predicted functioning, after controlling for symptoms and cognition. Finally, the study aimed to examine whether cognitive functioning was associated with functional impairment through its relationship with motivation to expend physical and cognitive effort. Method: Two cost-benefit decision-making tasks were developed to assess motivation to expend physical and cognitive effort in 44 MDD and 36 healthy comparison participants. Participants were assessed on a brief cognitive battery, anhedonia, depression severity, and functional impairment. Results: MDD participants made marginally fewer choices to expend high effort for large relative to small incentives than healthy comparison participants across both effort tasks. Lower motivation to expend physical effort in the MDD sample was moderated by increases in anhedonia severity, whereas lower cognitive effort motivation was associated with greater functional impairment, even after accounting for symptoms and cognitive ability. Cognitive effort motivation mediated the relationship between cognition and functioning in MDD. Conclusion: Motivation deficits to expend physical effort may reveal proximal mechanisms of anhedonia, while motivation for cognitive effort may explain distal functional outcomes. Findings offer novel evidence for attenuated motivation to expend physical and cognitive effort as a contributor to diagnostic clarity of anhedonia and a treatment target for functional recovery, respectively.