ROI definition.

We identified regions in which the BOLD response was parametrically modulated by the magnitude of the unsigned state prediction error (|δ|), using a threshold of p < 0.001 uncorrected, with cluster size > 10 voxels. Clusters identified were saved as binary ROIs (in SPM) and then combined into a single ROI using the MarsBaR toolbox (http://marsbar.sourceforge.net/). This functional ROI was then used for a subsequent RSA (see below). We divided the number of voxels that fell within both our functional ROI and each anatomical mask by the total number of voxels in our functional ROI. This gave us the percentage with which our functional ROI was a conjunction of each anatomical region.