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. 2016 Apr;37:36–43. doi: 10.1016/j.conb.2015.12.007

Figure 4.

Figure 4

ACC is active when internal models are updated not just when task difficulty increases because surprising events occur. On each trial of a saccade planning task, participants began by fixating a central cross. A target (coloured dot) appeared on a circular perimeter. Its location was predictable because target locations were similar over runs. However, two types of unexpected targets occurred. (a) On model update trials the new dot location was indicative of future dot locations. To signal those trials, the dot had a different colour. In the example, before the update, trials had red dots in the upper right and the model update trial had a blue dot in the lower right. (b) This was not the case on surprise only trials. There the dot colour was grey and future targets reverted to the original distribution (in the example to the upper right) (c) Plot of target locations (angle α from vertical) over 150 trials. Different coloured targets are from different runs. One-off targets are shown in grey. (d) Distribution of target locations within a run is a combination of a circular Gaussian, shown in red, and a uniform distribution, shown in black, from which one-off trials were drawn. (e) Whole-brain cluster-corrected fMRI analysis indicated a region spanning ACC and adjacent pre-supplementary motor area was the only area in which there was a significant effect of model updating (contrast shows all voxels with a parametric effect of DKL). The ROI denoted by the yellow line is the ACC region of interest analysed in panels E and F. (f) Mean effect size for surprise (IS) and updating (DKL) in the ACC ROI (error bars are SEM). (g) Raw activity in the ACC ROI plotted as a function of trial-in-run (0 on abscissa indicates model update or surprise trial, while trials 1, 2, 3, etc., are the trials following the model update or surprise trial. (e) At last, there are regions other than the dACC that are more active as a simple function of the reaction time, which is mostly a function of the difficulty of responding, similarly in one off and update trials (left and right panel).). Adapted from [26].