Faymonville et al.  selected 11 healthy volunteers (4 women, 7 men) who scored high on the Stanford Hypnotic Susceptibility Scale to participate in a study exploring the mechanisms of pain perception during the hypnotic state. Semi-structured interviews conducted during the selection process yielded information about the subjects’“pleasant life experiences” that were later used for the mental imagery portion of experimental sessions. For purposes of the study, hypnosis was defined by the presence of slow ocular movements in isolation or interspersed with rapid eye movement shifts; relaxed body posture; and response by a prearranged foot movement to verbal cue.

The volunteers were subjected to stimulation, both non-noxious (with warm water) and noxious (hot water, at about 47°C), during three different states: at rest (immobile, and told to “empty their mind”); while imagining a pleasurable memory; and during a hypnotic state. Two PET scans were performed during each of the six conditions, for a total of 12 scans per volunteer. Immediately after each scan, subjects were asked to rate the intensity and unpleasantness of the stimulus on a scale from 0 to 10. The order of the resting and mental imagery states was varied, but to avoid multiple hypnotic inductions, the fifth to eighth scans were performed in all subjects while they were under hypnosis.

Both pain sensation and unpleasantness of the noxious stimuli were reduced by hypnosis. The PET scans revealed an increase in regional cerebral blood flow in the thalamic nuclei, anterior cingulate, and insular cortices after noxious stimulation. An interaction analysis of the scans showed that the activity in the mid cingulate cortex related differently to pain perception and unpleasantness during the hypnotic state.