Bastien Blain, Guillaume Hollard, and Mathias Pessiglione
PNAS 2016 113 (25) 6967-6972
The ability to exert self-control is key to social insertion and professional success. An influential literature in psychology has developed the theory that self-control relies on a limited common resource, so that fatigue effects might carry over from one task to the next. However, the biological nature of the putative limited resource and the existence of carry-over effects have been matters of considerable controversy. Here, we targeted the activity of the lateral prefrontal cortex (LPFC) as a common substrate for cognitive control, and we prolonged the time scale of fatigue induction by an order of magnitude. Participants performed executive control tasks known to recruit the LPFC (working memory and task-switching) over more than 6 h (an approximate workday). Fatigue effects were probed regularly by measuring impulsivity in intertemporal choices, i.e., the propensity to favor immediate rewards, which has been found to increase under LPFC inhibition. Behavioral data showed that choice impulsivity increased in a group of participants who performed hard versions of executive tasks but not in control groups who performed easy versions or enjoyed some leisure time. Functional MRI data acquired at the start, middle, and end of the day confirmed that enhancement of choice impulsivity was related to a specific decrease in the activity of an LPFC region (in the left middle frontal gyrus) that was recruited by both executive and choice tasks. Our findings demonstrate a concept of focused neural fatigue that might be naturally induced in real-life situations and have important repercussions on economic decisions.
In evolved species, resisting the temptation of immediate rewards is a critical ability for the achievement of long-term goals. This self-control ability was found to rely on the lateral prefrontal cortex (LPFC), which also is involved in executive control processes such as working memory or task switching. Here we show that self-control capacity can be altered in healthy humans at the time scale of a workday, by performing difficult executive control tasks. This fatigue effect manifested in choice impulsivity was linked to reduced excitability of the LPFC following its intensive utilization over the day. Our findings might have implications for designing management strategies that would prevent daylong cognitive work from biasing economic decisions.
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