Roles of Ventromedial Prefrontal Cortex and Anterior Cingulate in Subjective Valuation of Prospective Effort

Abstract

The perceived effort level of an action shapes everyday decisions. Despite the importance of these perceptions for decision-making, the behavioral and neural representations of the subjective cost of effort are not well understood. While a number of studies have implicated anterior cingulate cortex (ACC) in decisions about effort/reward trade-offs, none have experimentally isolated effort valuation from reward and choice difficulty, a function that is commonly ascribed to this region. We used functional magnetic resonance imaging to monitor brain activity while human participants engaged in uncertain choices for prospective physical effort. Our task was designed to examine effort-based decision-making in the absence of reward and separated from choice difficulty—allowing us to investigate the brain’s role in effort valuation, independent of these other factors. Participants exhibited subjectivity in their decision-making, displaying increased sensitivity to changes in subjective effort as objective effort levels increased. Analysis of blood-oxygenation-level dependent activity revealed that the ventromedial prefrontal cortex (vmPFC) encoded the subjective valuation of prospective effort, and ACC activity was best described by choice difficulty. These results provide insight into the processes responsible for decision-making regarding effort, partly dissociating the roles of vmPFC and ACC in prospective valuation of effort and choice difficulty.

The Subjective Value of Cognitive Effort is Encoded by a Domain-General Valuation Network

“…Our conclusions align closely with a recent physical effort study, which found that the vmPFC encoded SV while the ACC tracked decision difficulty (Hogan et al, 2018). Interestingly, despite coming to the same conclusions as our own study, this study used methods more like those used in the prior cognitive effort studies.…”

“…Numerous studies have implicated a core valuation network that encodes SV across multiple domains (e.g., risk and delay), with primary foci in the ventromedial prefrontal cortex (vmPFC) and ventral striatum (VS; Levy and Glimcher, 2012; Bartra et al, 2013). Although this network was recently implicated in physical effort-based SV encoding (Hogan et al, 2018;Aridan et al, 2019), it has not been demonstrated to encode SV for choices about cognitive effort.…”

Neural mechanisms underlying the effects of physical fatigue on effort-based choice

“…Moreover, choice prospects only involved varying amounts of physical effort (i.e., no prospective rewards were involved), which allowed us to examine how fundamental processes related to effort valuation were influenced by fatigue-induced changes in bodily state, separate from effects associated with reward valuation or effort/reward trade-offs. We have previously used this choice set to extract computational parameters that capture an individual's subjective valuation of physical effort in a state of rest 9 .…”

“…Essentially, when individuals are faced with the option of exerting a certain amount of effort, versus a risky option involving either a greater amount of effort or no effort at all, they are less willing to choose the risky option while in a fatigued state. This hypothesis has its basis in previous studies of effort-based decision-making that found individuals exhibit increased sensitivity to changes in subjective effort as objective effort levels increase (i.e., risk aversion for effort) 6,7,9 . Neurally we hypothesize that decisions about prospective effort exertion have their basis in a value signal encoded in the ACC and insula.…”

“…Physical fatigue can result in a diminished willingness to exert effort that might be performed in a more rested state. Previous work has established a network of brain regions, including the anterior cingulate cortex (ACC), bilateral anterior insula, and ventromedial prefrontal cortex (vmPFC) in computing the value of effortful options and making effort-based decisions [1][2][3][4][5][6][7][8][9][10] . However this work has primarily focused on valuation and decision-making while in a rested state, and did not consider how physical fatigue might influence decisions to exert effort.…”