Table 2

Significant reductions in regional μ-opioid receptor availability in healthy human volunteers during sustained masseter muscle pain. Statistical parametric mapping analysis. Data represent the means ± SD of binding potential values in regions identified as showing significant reductions in μ-opioid receptor availability from placebo to sustained pain conditions in statistical parametric maps. Cluster size is expressed in 13-mm voxels. Zvalues refer to the comparison between placebo and painB max/K d values, within subjects. Percent change refers to the percent average change (± SD) between B max/K d values obtained in the placebo and pain scans, within subjects. No significant increases in μ-opioid receptor availability were observed in the pain condition with respect to the placebo condition. C, contralateral to the side of pain; I, ipsilateral to the side of pain; (8/9), Brodmann areas 8/9 of the prefrontal cortex.

RegionsPlacebo (Bmax/Kd)Pain (Bmax/Kd)Coordinates (x,y,z) (mm)Cluster size (voxels)ZPercent change
Anterior thalamus (C)1.81 ± 0.391.66 ± 0.366, –4, 4604 5.06–7.2 ± 12.0
Lateral thalamus (C)1.11 ± 0.310.97 ± 0.2515, –9, 153064.83–11.3 ± 13.9
Amygdala (I)1.83 ± 0.441.70 ± 0.35–24, 1, 194684.55–6.0 ± 11.1
Hypothalamus (C)1.15 ± 0.491.02 ± 0.3310, –2, –111134.61–3.9 ± 33.1
Significant after correction for cluster size
Cingulate cortex0.87 ± 0.140.77 ± 0.1510, –24, 4213353.49–10.7 ± 12.7
Anterior insula (C)1.09 ± 0.170.97 ± 0.1939, 23, –216053.97–10.5 ± 7.5
Prefrontal cortex (8/9) (I)0.85 ± 0.150.75 ± 0.16–20, –1, –5913703.30–11.0 ± 13.8
Prefrontal cortex (8/9) (C)0.84 ± 0.150.73 ± 0.15 32, 9, 5218764.17–12.3 ± 13.0