fMRI Statistical Analysis: The imaging experiments and analysis of subject-specific data will lead to maps corresponding to separate measures: resting state functional connectivity maps, and measures of cerebral blood flow (CBF). Final inferences will be made at the voxel level and for anatomically specific regions-of-interest (ROIs). The voxel-based analysis will be performed through the generation of summary images referred to as statistical parametric maps (SPMs) representing before-infusion vs. after-infusion, and, as data in the two patient groups become available, two-way ANOVA results of ketamine infusion state and patient diagnosis (chronic pain or refractory depression). The ROI-based analysis will be driven by the a priori selected fronto-limbic regions of interest generated in the self-reflection task, and by the anatomical nodes in the default mode network given in the literature.