Effect of expectation classification (Low vs High) on µ-opioid system activation. Left: expectation group effects (High > Low) on Δ in µ-opioid BPND after placebo administration (P < 0.001, k > 10 voxels) were found in the DLPFC. Upper Right: regions effect of expectation group on Δ in µ-opioid BPND after placebo administration in the DLPFC; lower right: no significant effect of expectations group on Δ VAS ratings after placebo administration was found.