Modulation of ventral striatal activity by cognitive effort

Abstract

Effort discounting theory suggests that the value of a reward should be lower if it was effortful to obtain, whereas contrast theory suggests that the contrast between the costly effort and the reward makes the reward seem more valuable. To test these alternative hypotheses, we used functional magnetic resonance imaging (fMRI) as participants engaged in feedback-based learning that required low or high cognitive effort to obtain positive feedback, while the objective amount of information provided by feedback remained constant. In the low effort condition, a single image was presented with four response options. In the high effort condition, two images were presented, each with two response options, and correct feedback was presented only when participants responded correctly to both of the images. Accuracy was significantly lower for the high effort condition, and all participants reported that the high effort condition was more difficult. A region of the ventral striatum selected for sensitivity to feedback value also showed increased activation to feedback presentation associated with the high effort condition relative to the low effort condition, when controlling for activation from corresponding control conditions where feedback was random. These results suggest that increased cognitive effort produces corresponding increases in positive feedback-related ventral striatum activity, in line with the predictions made by contrast theory. The accomplishment of obtaining a hard-earned intrinsic reward, such as positive feedback, may be particularly likely to promote reward-related brain activity.

Keywords: Contrast theory; Effort; Effort discounting; Striatum; Trial-and-error learning; VMPFC.

Figure 1

Depiction of trials for 1-step (low effort) and 2-step (high effort) conditions. 1-step random and 2-step random conditions resembled the above set-up; however, random feedback did not reflect performance accuracy.

Figure 2

A. Accuracy for the two learning conditions. There is a significant difference in performance between the 1-step (low effort) and 2-step (high effort) conditions. B. Learning accuracy by block for the two learning conditions. Chance performance is at 25%.

Figure 3

A. Brain activity showing sensitivity to positive vs. negative feedback presentation (difficulty and contingency collapsed) (p < 0.05, corrected for multiple comparisons). B. For illustrative purposes, beta weights from the voxels of the left VS showing sensitivity to positive vs. negative feedback

Figure 4

Beta weights from the voxels of the left VS showing an effect of high > low effort. Random conditions are included in the contrast as a control.