The ventral striatum is believed to encode the subjective value of cost/benefit options; however, this effect has strikingly been absent during choices that involve physical effort. Prior work in freely-moving animals has revealed opposing striatal signals, with greater response to increasing effort demands and reduced responses to rewards requiring effort. Yet, the relationship between these conflicting signals remains unknown. Using fMRI with a naturalistic, effort-based navigation paradigm, we identified functionally-segregated regions within ventral striatum that separately encoded action, effort, and discounting of rewards by effort. Strikingly, these sub-regions mirrored results from a large-sample connectivity-based parcellation of the striatum. Moreover, individual differences in striatal effort activation and effort discounting signals predicted striatal responses to effort-related choices during an independent fMRI task. Taken together, our results suggest that a dorsomedial region primarily associated with action may instead represent the effort cost of actions, and raises fundamental questions regarding the interpretation of striatal "reward" signals in the context of effort demands.
