Neural mechanisms of antinociceptive effects of hypnosis

Background The neural mechanisms underlying the modulation of pain percepti on by hypnosis remain obscure. In this study, we used positron emission tom ography in 11 healthy volunteers to identify the brain areas in which hypno sis modulates cerebral responses to a noxious stimulus. Methods: The protocol used a factorial design with two factors: state (hypn otic state, resting state, mental imagery) and stimulation (warm non-noxiou s vs. hot noxious stimuli applied to right thenar eminence). Two cerebral b lood flow scans were obtained with the O-15-water technique during each con dition. After each scan, the subject was asked to rate pain sensation and u npleasantness, Statistical parametric mapping was used to determine the mai n effects of noxious stimulation and hypnotic state as well as state-by-sti mulation interactions (i.e., brain areas that would be more or less activat ed in hypnosis than in control conditions, under noxious stimulation). Results: Hypnosis decreased both pain sensation and the unpleasantness of n oxious stimuli. Noxious stimulation caused an increase in regional cerebral blood flow in the thalamic nuclei and anterior cingulate and insular corti ces. The hypnotic state induced a significant activation of a right-sided e xtrastriate area and the anterior cingulate cortex. The interaction analysi s showed that the activity in the anterior (mid-)cingulate cortex was relat ed to pain perception and unpleasantness differently in the hypnotic state than in control situations. Conclusions: Both intensity and unpleasantness of the noxious stimuli are r educed during the hypnotic state. in addition, hypnotic modulation of pain is mediated by the anterior cingulate cortex.