Figure 1.

Psychological mechanisms such as verbally-induced expectations, cued and contextual conditioning and social learning trigger the cascade of endogenous opioids and non-opioids. The result is an alteration of the pain experience that at least in part, induces an active inhibition of nociceptive activity and modulation of brain areas predicting placebo analgesic responses.

PFC, prefrontal cortex; ACC, anterior cingulate cortex; SI, primary somatosensory cortex; SII secondary somatosensory cortex; PAG, periacqueductal gray.