Stress and Motivation: An fMRI Study on the Effects of Stress on Effort-Based Decision- Making

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Reaching desired goals requires effort. In daily life, we often face important decisions on whether to engage in effortful yet rewarding actions (e.g., studying hard to obtain a university degree or accepting a demanding job with a great salary). These decisions are often made under considerable stress, such as when having financial uncertainty. Previous studies have shown that effort-based decision-making implicates a cortico-subcortical network involving the prefrontal cortex and midbrain catecholamine (noradrenaline and dopamine). Stress is known to affect both prefrontal activity and catecholamine levels. Despite these commonalities, the effect of stress on effort-based decision-making and its neural correlates are surprisingly understudied. In this study, the effects of stress on effort-based decision-making were investigated, focusing on behaviour, neural activity, and noradrenergic release measured by pupil dilation. Using a within-subjects design with acute stress induction, we hypothesized that stress would decrease the willingness to engage in mental effort, and that this would be linked with alterations in prefrontal activity and pupil dilation. Participants performed an effort-based decision-making task in the functional magnetic resonance imaging (fMRI) scanner during a control condition or an experimentally induced acute stress condition. The results showed that stress reduced the willingness to engage in effort. Pupil dilation increased with task difficulty during calculations, but did not change under stress. Unexpectedly, no difference was observed between stress and control at the whole-brain level. An a-priori region-ofinterest analysis revealed no significant effect of stress on effort or reward coding in the anterior cingulate cortex (ACC). A significant decrease in effort coding under stress in the dorsolateral prefrontal cortex (DLPFC) was observed. However, this was specific to the high reward condition and for participants who experienced the control session first. Overall, these results suggest that acute stress reduces the willingness to engage in mental effort, with preliminary evidence of alterations in DLPFC. KEYWORDS stress, effort-based decision-making, DLPFC, MPFC, ACC, motivation, effort, reward
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