Temporal Dynamics of Neural Computations for Stimulus Value and Effort Cost

Abstract

We often make decisions not only based on an item's value, but also the effort required to obtain it: e.g., using a vending machine versus walking to a café. Whereas good-based value is represented in ventromedial prefrontal cortex (vmPFC), recent data has implicated dorsomedial frontal cortex (dmFC) in integrating stimulus value with effort cost to derive net (combined) value. However, the temporal dynamics of net value computation remain unclear. Here we examined this question using event-related potentials (ERP) while hungry subjects decided whether to work at different levels of physical effort cost (low, medium, or high grip strength) for the opportunity to obtain food. Subjects' decisions generally incorporated both stimulus value and effort cost, as indicated by significant logistic fits to their choice curves. Parametric ERP responses associated with net value were visible from 100-300 ms after stimulus onset, negatively correlated with effort cost, and from ~450-650 ms, positively correlated with stimulus value. Distributed reconstruction of stimulus-locked responses revealed significant sources in the vmPFC, but not dmFC. In contrast, response-locked signals were chiefly localized to dmFC and superior parietal sources rather than vmPFC, and largely reflected effort cost computations preceding response. Together, these data suggest that localization of net value integration to vmPFC and dmFC sources depends on whether the data is time-locked to the onset of stimulus or response. In line with a transition from good-based to action-based valuation, computations of effort cost may play an increasing role in dmFC activity in the time directly leading up to choice.

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