Abstract
From a gym workout, to deciding whether to persevere at work, many activities require us to persist in deciding that rewards are ‘worth the effort’ even as we become fatigued. However, studies examining effort-based decisions typically assume that the willingness to work is static. Here, we use computational modelling on two effort-based tasks, one behavioural and one during fMRI. We show that two hidden states of fatigue fluctuate on a moment-to-moment basis on different timescales but both reduce the willingness to exert effort for reward. The value of one state increases after effort but is ‘recoverable’ by rests, whereas a second ‘unrecoverable’ state gradually increases with work. The BOLD response in separate medial and lateral frontal sub-regions covaried with these states when making effort-based decisions, while a distinct fronto-striatal system integrated fatigue with value. These results provide a computational framework for understanding the brain mechanisms of persistence and momentary fatigue.
Highlights
From a gym workout, to deciding whether to persevere at work, many activities require us to persist in deciding that rewards are ‘worth the effort’ even as we become fatigued
Participants could freely choose to rest, and prevent a significant build-up of fatigue, a repeated measures t-test revealed that ratings of fatigue were higher at the end of the experiment than at the beginning (t(34) = 4.27, two-tailed p < 0.001, Cohen’s d = 0.72, 95% Confidence intervals (CIs) = [0.54, 1.52]; Supplementary Fig. 2)
We show that two hidden states, one longer-term unrecoverable and one short-term recoverable, impact on people’s decisions to work and exert effort for reward on a trial-by-trial basis
Summary
To deciding whether to persevere at work, many activities require us to persist in deciding that rewards are ‘worth the effort’ even as we become fatigued. The BOLD response in separate medial and lateral frontal sub-regions covaried with these states when making effort-based decisions, while a distinct fronto-striatal system integrated fatigue with value These results provide a computational framework for understanding the brain mechanisms of persistence and momentary fatigue. Activity in sub-regions of the supplementary motor area (SMA)/anterior cingulate cortex (ACC), the middle frontal gyri (MFG), frontal pole (FP), and ventral striatum (VS) have been implicated in computing value and motivating the exertion of effort[4,5,7,26,27,28,29,30,31,32] Evidence suggests that these regions change their response with time on task[13,15,17]. Do separate sub-regions within this network signal fatigue on different timescales and integrate this into computations of value?
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