The Neurobiology of Cognitive Fatigue and Its Influence on Effort-Based Choice.

Feelings of cognitive fatigue emerge through repeated mental exertion and are ubiquitous in our daily lives. However, there is a limited understanding of the neurobiological mechanisms underlying the influence of cognitive fatigue on decisions to exert. We use functional magnetic resonance imaging while participants (18 female, 10 male) choose to exert effort for reward, before and after bouts of fatiguing cognitive exertion. We found that when participants became cognitively fatigued, they were more likely to choose to forgo higher levels of reward for more effort. We describe a mechanism by which signals related to cognitive exertion in dlPFC influence effort value computations, instantiated by the insula, thereby influencing an individual's decisions to exert while fatigued. Our results suggest that cognitive fatigue plays a critical role in decisions to exert effort and provides a mechanistic link through which information about cognitive state shapes effort-based choice.Significance statement Cognitive fatigue influences decisions to exert effort throughout our daily lives. However, it is unclear how the brain integrates information about cognitive fatigue to influence effort-based decision-making. We found that when individuals engage in repeated cognitive exertion, exertion-related signals in dlPFC influence effort value computations in insular cortex, thereby influencing an individual's decisions to exert while fatigued. These results provide a mechanistic account of how information about cognitive state impacts choice.