Effort and valuation in the brain: the effects of anticipation and execution

Abstract

Neural representations of the effort deployed in performing actions, and the valence of the outcomes they yield, form the foundation of action choice. To discover whether brain areas represent effort and outcome valence together or if they represent one but not the other, we examined these variables in an explicitly orthogonal way. We did this by asking human subjects to exert one of two levels of effort to improve their chances of either winning or avoiding the loss of money. Subjects responded faster both when exerting greater effort and when exerting effort in anticipation of winning money. Using fMRI, we inspected BOLD responses during anticipation (before any action was executed) and when the outcome was delivered. In this way, we indexed BOLD signals associated with an anticipated need to exert effort and its affective consequences, as well as the effect of executed effort on the representation of outcomes. Anterior cingulate cortex and dorsal striatum (dorsal putamen) signaled the anticipation of effort independently of the prospect of winning or losing. Activity in ventral striatum (ventral putamen) was greater for better-than-expected outcomes compared with worse-than-expected outcomes, an effect attenuated in the context of having exerted greater effort. Our findings provide evidence that neural representations of anticipated actions are sensitive to the expected demands, but not to the expected value of their consequence, whereas representations of outcome value are discounted by exertion, commensurate with an integration of cost and benefit so as to approximate net value.

Figure 1.

Cue predictive task dissociates anticipation and outcome processing from motor execution. In each trial, one of four possible images that predicts effort-valence combination appeared on the screen and, after a jittered delay, participants executed the squeeze, followed by a fixed delay and a probabilistic outcome (20/0 pence for win, 0/−20 pence for avoid loss condition). After a randomized intertrial interval of 0.75–1.5 s length, the next trial commenced. At grip onset, participants saw a “YOU” message giving them 1.5 s to respond by squeezing either to the low or high effort level (indicated by a white tick mark). The purple dotted line in the schema indicates that half of the trials did not include actual squeezing, but instead participants saw a green bar moving upward, indicating that these were computer-executed trials. Participants knew that whether they had to squeeze was probabilistic and that this fact was only indicated when they saw the “YOU” or “COMPUTER” text at the end of the fixation period. Participants fully learned the contingencies between the different fractal images and task requirements before scanning.

Figure 2.

A,. Force data from one trial from one subject with its sigmoid fit line and first derivative to smooth the data. From this function, we use a threshold to find the asymptote speed (force at asymptote/time to asymptote) and RT (in milliseconds). B, C, Group-averaged asymptote speed in force/second (B) and RT in milliseconds (C) showing significant main effects of effort and valence. Interactions were nonsignificant. D, Speeded RT based on outcome of previous trial. Participants speeded their response after a loss, speeding after loss was significantly higher than speeding after both zero and win. Error bars indicate SEM.

Figure 3.

SPM of brain activity for cue presentation. Fractal images indicating high effort elicited greater activity in supplementary motor area (SMA), anterior cingulate cortex (ACC), and dorsal striatum (dorsal putamen) than fractal images indicating low effort did (p < 0.05 FWE; whole brain, SVC within bilateral ACC ROI, SVC within bilateral striatum ROI, respectively). Coordinates are given in MNI space. L indicates left; R, right. For illustrative purposes, voxels displayed in gray on glass brain and in yellow on slices survived a threshold of p < 0.001, uncorrected.

Figure 4.

SPM of brain activity at the time of outcome presentation. A, B, Glass brain and coronal slice show that activity in bilateral vSTR was stronger for better outcomes than worse outcomes, regardless of valence, corrected for FWE (p < 0.05), peak voxels; Left: −21, 5, −8, Right: 21, 8, −8. For illustrative purposes, voxels displayed in gray on glass brain and in yellow on coronal slice survived a threshold of p 0.001, uncorrected. B, Inset, Functional ROI's at left and right vSTR (putamen) from FWE-corrected voxels (p < 0.05) from whole-brain analysis centered at the peak of activity. Left, 13 voxels. Right, Three voxels. C, Axial slice of the same functional ROIs shown in B, inset. Coordinates are given in MNI space. L indicates left; R, right. D, Extracted activity within functional ROIs shown in B, inset, and in C, revealing an effort-by-outcome interaction. Regardless of valence, the difference between better > worse outcomes after expending low effort is significantly greater than after expending high effort. Error bars indicate SEM.

Figure 5.

SPM of brain activity at the time of outcome presentation showing greater signal in bilateral insula when receiving worse outcomes than better outcomes, regardless of effort (p < 0.05 FWE). For illustrative purposes, voxels displayed in gray on glass brain and in yellow on coronal slice survived a threshold of p < 0.001, uncorrected. Coordinates are given in MNI space. L indicates left; R, right. The bar graph on the right depicts a valence-by-outcome interaction of extracted activity within insula ROIs. Regardless of effort, the difference between worse > better outcomes is greater in avoid losing conditions compared with in winning conditions. Error bars indicate SEM.