The image parameters used were as follows: matrix size, 64 × 64; voxel size, 3 × 3 mm; echo time, 40 ms; repetition time, 2000 ms. A functional image volume comprised 32 contiguous slices of 3 mm thickness (with a 1 mm interslice gap), which ensured that the whole brain was within the field of view. Data were
preprocessed using SPM2 (Wellcome Department of Cognitive Neurology, London). Following correction for head motion and slice acquisition timing, functional data were spatially normalized to a standard template brain. Selleckchem GSK1210151A Images were resampled to 5 mm cubic voxels and spatially smoothed with a 10 mm full width at half-maximum isotropic Gaussian kernel. A 256 s temporal high-pass filter was applied in order to exclude low-frequency artifacts. Temporal correlations were estimated using restricted maximum likelihood estimates of variance components
using a first-order autoregressive model. The resulting nonsphericity was used to form maximum likelihood estimates of the activations. Data were analyzed in a modified version of SPM2. By default, SPM2 orthogonalizes each parametric regressor in turn with respect to those already entered; we ensured that no orthogonalization was used in any analysis. We analyzed our fMRI data via two design matrices. In the first, we entered: (1) the main Autophagy inhibition effect of stimulus presentation; (2–4) parametric regressors for choice value predicted by the Bayesian, QL, and WM models; (5) the main effect of volatility; (6–8) the interaction between volatility and choice value for the three models; (9) the main effect of feedback; (10) a parametric regressor encoding the valence of the feedback; (11–13) parametric regressors encoding prediction error signals predicted by the Bayesian, QL, and WM models; (14) a nuisance below regressor
encoding the mean fMRI signal from 1000 randomly selected voxels from outside the brain; and (15–20) nuisance regressors encoding realignment parameters (see Figure S2 for an example design matrix). Analyses described in Figure 3 (expected value/decision entropy) pertain to regressors 2–4 (note that decision entropy = 1-choice value); analyses described in Figure 4 (interaction with volatility) pertain to regressors 5–8. Note that main effects of decision- and feedback-related activity for each model, and their interaction with volatility, are all entered simultaneously into this design matrix, and so the results described reflect unique variance associated with each of these predictors. Results for the common variance can be seen in Figures S1A and S1B.