Neural mechanisms underlying the impact of daylong cognitive work on economic decisions

Blain, Bastien; Hollard, Guillaume; Pessiglione, Mathias · 2016 · OpenAlex-citations

DOI: 10.1073/pnas.1520527113

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Summary

This study investigates the neural mechanisms underlying how prolonged cognitive work affects economic decision-making, specifically addressing the controversial theory of "ego depletion." The authors sought to determine if self-control relies on a limited resource that depletes over time, thereby increasing impulsivity in subsequent tasks. Previous research often failed to replicate these effects, potentially due to insufficient duration of cognitive load. To address this, the researchers extended the time scale of fatigue induction to approximate a full workday (over 6 hours), targeting the lateral prefrontal cortex (LPFC), a region known to support both executive control and self-regulation. The experimental design involved 58 healthy adults divided into three groups: a "hard" group performing difficult executive tasks (3-back working memory and 12-switch tasks), an "easy" group performing simpler versions (1-back and 1-switch), and a "leisure" group engaging in non-cognitive activities. Participants performed these tasks in 30-minute sessions interspersed with intertemporal choice trials, where they chose between immediate and delayed monetary rewards. Functional MRI (fMRI) was conducted at the beginning, middle, and end of the day for a subset of participants to monitor neural activity. The study aimed to isolate whether the difficulty of executive tasks, rather than mere boredom or time passage, caused changes in LPFC activity and choice impulsivity. Behavioral results demonstrated that choice impulsivity significantly increased over the day only in the hard condition, where participants increasingly favored immediate rewards. This increase was not observed in the control groups (easy and leisure conditions), nor was it correlated with baseline impulsivity or changes in response time. Executive task performance remained relatively stable across sessions, indicating that the fatigue effect was specific to decision-making rather than general cognitive decline. fMRI data revealed that the increase in impulsivity was associated with a specific decrease in activity within the left middle frontal gyrus, a region of the LPFC recruited by both the executive tasks and the intertemporal choices. This neural reduction was absent in the control groups, confirming that the fatigue effect was driven by the intensive utilization of LPFC resources. The findings provide evidence for a concept of "focused neural fatigue," demonstrating that daylong engagement in demanding executive control tasks can biologically alter self-control capacity. The study links behavioral impulsivity directly to reduced excitability in the LPFC following prolonged use, offering a neural explanation for ego depletion that previous short-duration studies may have missed. These results have significant implications for understanding how real-world cognitive demands, such as those encountered in professional settings, can bias economic decisions toward short-term gratification. The authors suggest that management strategies should account for this neural fatigue to prevent impaired decision-making during periods of sustained cognitive work.

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• executive function