Left and right NAcc regions of interest (ROIs) were obtained using FMRIB's Integrated Registration and Segmentation Tool (FIRST), distributed with FMRIB Software Library (FSL). FIRST is a method to do automatic segmentation of subcortical structures, including NAcc, in human brain MRI (Patenaude et al., 2011). Left and right NAcc were combined in one ROI, which was used for our analyses. The ROIs were created in MNI atlas space and then converted to Talairach atlas space. All subsequent operations were performed on the Talairach atlas-transformed NAcc ROI.
