Fatigue Symptoms Influence Effort-Based Decision-Making in Major Depressive Disorder

Fatigue is a central symptom of major depressive disorder (MDD). Studies in healthy individuals suggest that fatigue reduces willingness to exert effort, but its role in effort-based decision making in MDD remains unclear. Here, we examined how fatigue and depressed mood influence cognitive effort-based choices in individuals with MDD.

Healthy participants (n = 26) and individuals with MDD (n = 18) completed a forced-choice paradigm in which they chose between a low-effort cognitive task for a small reward and a more demanding task for a larger reward. Participants also completed the Beck Depression Inventory (BDI) and Modified Fatigue Impact Scale (MFIS) to assess depressive symptoms and fatigue severity.

Individuals with MDD reported significantly greater fatigue severity compared with healthy control participants. Across participants, higher MFIS scores were associated with a reduced willingness to select cognitively effortful options, particularly at higher effort levels. Fatigue severity explained choice behavior better than diagnostic group or depressive symptom severity measured by the BDI. These findings suggest that fatigue, rather than depressed mood alone, is a key factor shaping cognitive effort-based decision making in MDD.

Our findings demonstrate that fatigue substantially influences willingness to exert cognitive effort. These results provide insight into mechanisms underlying reduced goal-directed behavior in depression and may help guide interventions targeting fatigue-related motivational impairments.