Behavioral studies have suggested that placebo analgesia is partly mediated by the
endogenous opioid system. Expanding on these results we have shown that the opioid-
receptor-rich rostral anterior cingulate cortex (rACC) is activated in both placebo and opioid
analgesia. However, there are also differences between the two treatments. While opioids
have direct pharmacological effects, acting on the descending pain inhibitory system,
placebo analgesia depends on neocortical top-down mechanisms. An important difference …