Figure 5.

a, Overlap between anatomical ROIs depicted on the average anatomical image of the subjects. Darker red (right NAC) and blue (left NAC) denote a higher degree of overlap between the ROIs of different subjects. b, The raw BOLD signal (in arbitrary units) as extracted from the ROIs in a, aligned on trial onset, averaged over all subjects and all trials, and separated according to chosen stimulus and payoff. Shading corresponds to the SEM for each trace. Compare with e. c, Illustration of the theoretical asymptotic prediction errors for each stimulus. Stimuli (presented at time t = 0) appear unpredictably and so induce prediction errors approximately equal to their mean values (40 and 20 for the sure stimuli and 20 for risky stimulus, ignoring subject-specific risk-related perturbations for purposes of illustration only). For the sure stimuli, the outcomes (at t = 5) are fully predicted, and thus induce no further prediction errors. For the 0/40¢ stimulus, the 40¢ outcome induces a positive prediction error (red solid line) of ∼20; the 0¢ outcome induces a negative prediction error of approximately (−20) (red dashed line). The 0¢ stimulus (data not shown) is not expected to generate a prediction error at time of stimulus onset or payoff. d, The canonical hemodynamic response function. e, Model prediction errors at the time of the stimulus and outcome for every subject for each condition (using individual best-fit parameters for the RSTD model) were convolved with the hemodynamic response function (d) and averaged to predict the grand average BOLD signal. The hemodynamic lag adds 5 s to the times to peak (dashed black lines). The yellow trace corresponds to the 0¢ stimuli and is below baseline due to the residual dip from the hemodynamic response in the previous trial.