Physical effort paradox during reward evaluation and links to perceived control

Effort expenditure not only prospectively discounts the reward associated with it but also retrospectively adds the subjective value of reward, which is known as the effort paradox. This study aimed to resolve the effort paradox during reward evaluation through the critical lens of neural dynamics and its potential moderators. In total, 40 participants completed an effort-reward task wherein they exerted varying physical efforts to obtain an opportunity to win monetary rewards by active or passive decision-making. We found that after-effects of physical effort expenditure during reward evaluation unfolded as an effort paradox over time, manifesting itself as an effort discounting effect during the reward positivity (RewP) period but as an effort enhancement effect during the late positive potential (LPP) interval. Then, we found a dynamic balance between the discounting effect and the enhancement effect such that the more effort discounted the RewP at the early stage, the more effort increased the LPP at the late stage. Moreover, we observed that the effort-reward relationship was modulated by perceived control such that it increased the reward sensitivity effect and decreased the effort discounting effect. Together, our findings provide new insights into the neural mechanisms underlying the after-effects of physical effort exertion during reward evaluation.