rostro-caudal extents spanning +56 mm to +36 mm in MNI space. mPFC has a superior extent of +14 mm and an inferior extent of −6 mm, while vmPFC spans −6 mm to −22 mm. Lateral extents were defined by conjoining the ROI boxes with the gray matter voxels in a smoothed (6 mm FWHM) gray matter mask (Figure 2). The VTA was approximated with an 8 mm diameter sphere centered on [0, −18, −12] (also see Kareken et al., 2004). The ventral striatum (Figure 2, right) was defined using rules developed by Malawi et al. (2001). As the caudate head also projects to the medial frontal area (Chiba, Kayahara, & Nakano, 2001; Haber et al., 2006), we also defined caudate head ROIs spanning from +26 mm rostrally to 0 mm (the anterior commissure) caudally, approximating areas mapped by Haber et al. (2006). The MarsBar utility (Brett, et al, 2002; http://marsbar.sourceforge.net/) was used to extract the mean AO and ApCO contrast value (i.e., the output of the subject-specific fixed effect model) from each ROI, within each of the subjects.
