Examining Effects of Effort and Reward Magnitude on Effort-Cost Decision-Making in People with Major Depressive Disorder

Background: Motivational impairment is a primary feature of major depressive disorder (MDD), yet the cognitive mechanisms underlying this deficit remain unclear. Effort-cost decision making (decisions regarding whether outcomes are worth the effort required to obtain them) is a popular framework for understanding motivation in MDD. This study examined whether ECDM deficits in MDD are driven by 1) reduced reward sensitivity, 2) increased effort sensitivity, or 3) both. Method: Individuals with MDD (N=32) and healthy controls (HC, N=30) completed the Apple Gathering Task. Participants decided whether an amount of effort (handgrip squeeze) was worth a reward (points). Reward and effort were parametrically manipulated to independently estimate effects of effort and reward. Results: Compared to HC, individuals with MDD were less willing to accept offers with low reward and low expected value (high effort requirements and low reward). Computational analyses using a Hierarchical drift diffusion modeling (DDM) mirrored these findings, suggesting that evidence accumulation in MDD compared to HC was 1) faster when rejecting high effort options, 2) slower when accepting high reward options. Additionally, higher fatigue was associated with reduced ECDM in those with MDD, particularly for offers with high effort and low expected value.Conclusion: Our results provide support that reduced ECDM in MDD reflects both diminished reward valuation and heightened effort valuation. Further, we found that fatigue severity was associated with reduced ECDM. These results contribute to a growing body of evidence showing reduced ECDM in MDD and identifies the role that fatigue has in shaping these impairments.