Neural mechanisms underlying the effects of cognitive fatigue on physical effort-based choice

Fatigue is a state of exhaustion that influences our willingness to engage in effortful tasks. While both physical and cognitive exertion can cause fatigue, there is a limited understanding of how fatigue in one exertion domain (e.g., cognitive) affects decisions to exert in another (e.g., physical). We use functional magnetic resonance imaging (fMRI) to measure brain activity while human participants make decisions to exert prospective physical effort before and after engaging in a cognitively fatiguing working memory task. Using computational modeling of choice behavior, we show that fatiguing cognitive exertion increases participants' subjective costs of physical effort compared to a baseline rested state. We describe how signals related to fatiguing cognitive exertion in the dorsolateral prefrontal cortex influence physical effort value computations instantiated by the insula, thereby increasing an individual's subjective valuation of prospective physical effort while cognitively fatigued. Our results support the idea of a general fatigue signal that integrates exertion-specific information to guide effort-based choice.