Imaging results for the main effect of intensity and for the interaction of treatment by intensity.

Main effect of intensity across treatment thresholded at p<0.001 uncorrected and small volume corrected (at p<0.001) using the AAL-template [24] for the region listed, except for the PAG(†), for which the seed voxel [3 −21 −3] from [9] was used. Treatment (naloxone vs saline session) by intensity (painful vs non-painful rating) interaction. Small volume corrected using the AAL-template of the left anterior cingulate cortex. AAL = automated anatomical labeling, SVC = small volume corrected, PAG = peri-aqueductal gray, ACC = anterior cingulate cortex *All p-values listed are family-wise-error corrected.