Expected Costs of Mental Efforts are Updated When People Exert Effort, not by Prospective Information

To understand human behaviour, it is crucial to reveal the mechanisms by which we learn and decide about effort costs and benefits in an uncertain world. Whereas the mechanisms for reward learning are well-understood, the mechanisms for effort cost learning, and especially mental effort, remain elusive. Initially, we hypothesized that cost learning follows temporal-difference learning such that brains update expected costs when informed about upcoming effort levels. However, fMRI data revealed neural correlates of a cost-prediction error of mental effort during task execution and not in response to an effort cue about upcoming effort demands. These results imply that expected costs are updated during actual effort exertion, implying that the adaptive learning of mental effort cost does not follow traditional temporal-difference learning. This study contributes to the understanding of the neural mechanism underlying unwillingness to work, suggesting that humans learn mental effort costs only when they experience effort exertion. ### Competing Interest Statement The authors have declared no competing interest.