Figure 1.
Task structure and behavioral performance.
a. Block types. In every block only one trial type is presented, where only one feature is manipulated. In a trial in the reward block, the cue informs about the final reward being small or big. In a trial in the effort block, the cue informs about the difficulty level (low or high). In the delay block, the cue informs about the length of the delay between response and reward delivery (short or long). b. Task structure and timing. The cue presentation is followed by a fixation symbol. The task follows, consisting of an addition followed by a subtraction. Two possible results are presented and the subject has to choose the correct one. After the response, a delay can occur. If the response was accurate, the reward is shown. c. Average rating of pleasantness for every cue-type (small reward cue, big reward cue, low effort cue, high effort cue, short delay cue, long delay cue). e. Average reaction times (RTs) in every condition (small reward, big reward, low effort, high effort, short delay, long delay). RT in the high effort condition is significantly higher than in the low effort condition (p<0.001).
Figure 2.
a. Reward contrast (big reward>small reward). Activation clusters are located in the posterior cingulate cortex (PCC), anterior cingulate cortex (ACC), striatum and superior frontal gyrus (SFG). b. Effort contrast (high effort>low effort). Activation clusters are located in the posterior cingulate cortex (PCC), brainstem, anterior cingulate cortex (ACC), insula, striatum and middle frontal gyrus (MFG). c. Conjunction of high effort>low effort & big reward>small reward. Overlapping activation clusters are located in the striatum, anterior cingulate cortex (ACC) and precuneus. d. Short delay>long delay contrast. The activation cluster is located in the left orbitofrontal cortex (OFC). e. Effort-selective activation ((high effort>low effort)>(high reward> low reward)), SVC for the region of the brainstem, p value 0.05 FWE correction for multiple comparisons, plotted on Proton Density Weighted MRI Template (left image). f. Parameter estimates plot at voxel −4, −32, −10 (MNI coordinates), local maximum in the activation cluster located in the Brainstem in the effort-selective contrast.
Table 1.
Summary of the activation clusters in the whole-brain contrasts.
Table 2.
List of regions resulting from the overlap of the Reward and Effort contrast, thus responding to both anticipation of high effort and big reward.