Figure 1.
Effects of pain and placebo on the activation of μ-opioid receptor-mediated neurotransmission. After correction for multiple comparisons, significant μ-opioid system activations during the sustained pain challenge (n = 14) were obtained in the dorsal anterior cingulate [DACing; x,y,z coordinates (in millimeters), 17, 10, 40; cluster size, 715 mm3; z score = 5.54; p < 0.005 after correction for multiple comparisons], medial prefrontal cortex (MPFC; x,y,z, 8, 45, -5; cluster size, 1064 mm3; z score = 3.90;p < 0.001), right (contralateral to pain) insular cortex (Ins; x,y,z, 49, 16, 6; cluster size, 257 mm3; zscore = 4.32; p < 0.005), ventral basal ganglia, bilaterally [nucleus accumbens (NAcc) extending to the ventral pallidum; right, x,y,z, 12, 4, -2, cluster size, 1700 mm3, z score = 9.26, p < 0.0001; left, x,y,z, -19, 9, 4, cluster size, 2177 mm3, z score = 4.32, p < 0.005], medial thalamus (Tha; x,y,z, -3, -15, 7; cluster size, 2283 mm3; z score = 6.49; p < 0.0001), right amygdala (Amy; x,y,z, 25, -2, -21; cluster size, 464 mm3; z score = 6.34; p < 0.0001), left subamygdalar temporal cortex (x,y,z, -28, 10, -38; cluster size, 560 mm3; zscore = 5.36; p < 0.005), and periaqueductal gray (x,y,z, -5, -28, -3; cluster size, 122 mm3; zscore = 3.56; p < 0.05). Significant effects of placebo on the activation of the μ-opioid system (n = 14) were detected in the left dorsolateral prefrontal cortex (DLPFC; x,y,z peak coordinates, -36, 13, 39; cluster size, 1403 mm3; z score = 4.27; p < 0.0001), rostral anterior cingulate (RACing; x,y,z, 14, 49, 13; cluster size, 3193 mm3; z score = 4.18; p < 0.0001), left NAcc (x,y,z, -7, 11, -11; cluster size, 1332 mm3; z score = 4.83; p < 0.0001), and right anterior insula (Ins; x,y,z, 41, 10, -17; cluster size, 844 mm3; z score = 4.15; p < 0.05). The posterior right insula achieved subthreshold levels of significance (x,y,z, 44, -15, 4; cluster size, 732 mm3; z score = 3.81; p < 0.0001 uncorrected for multiple comparisons). z scores of statistical significance are represented by the pseudocolor scale on the right side of the image and are superimposed over an anatomically standardized MRI image in coronal views. The left side of the axial and coronal images corresponds to the right side of the body (contralateral to pain; radiological convention). A map of μ-opioid receptor distribution is shown in the top right corner of the figure in a sagittal view, with binding potential (BP) values (receptor availability in vivo; Bmax/Kd) depicted by the same pseudocolor scale.