Abstract:

Expectation can bidirectionally regulate diseases or sensory experiences. In terms of pain field, positive expectation alleviates pain (i.e., placebo effect); while negative expectation makes it worse (i.e., nocebo effect). So far, most of researches on placebo and nocebo effect mainly come from the field of pain. Interestingly, although placebo and nocebo share similar psychological processes in modulating pain, the neurophysiological mechanisms underlying the placebo and nocebo are different. Placebo analgesia might be involved with endogenous opioids system. On the contrary, the nocebo effect is considered to be mediated by cholecystokinin (CCK). In addition, brain imaging researches suggested that placebo and nocebo could lead to contrary activation patterns in pain-related networks. Some areas such as the hippocampus were specifically activated in nocebo condition.

Key words: expectation, placebo, nocebo, pain