Effects of hypnosis on diffuse noxious inhibitory controls

The neurophysiological mechanisms of hypnotic analgesia are still under deb ate. It is known that pain occurring in one part of the body (counterstimul ation) decreases pain in the rest of the body by activating the diffuse nox ious inhibitory controls (DNICs). The aim of this study was to explore the effects of hypnosis on both pain perception and heterotopic nociceptive sti mulation. The A forms of both the Harward Group Scale of Hypnotic Susceptib ility and the Stanford Hypnotic Susceptibility Scale were administered to 5 0 healthy students. Twenty subjects were selected and assigned to two group s: group A, consisting of 10 subjects with high hypnotic susceptibility; an d group B, consisting of 10 subjects with low hypnotic susceptibility. The subjects were then randomly assigned first to either a control session or a session of hypnotic analgesia. The nociceptive flexion reflex (RIII) was r ecorded from the biceps femoris muscle in response to stimulation of the su ral nerve. The subjective pain threshold, the RIII reflex threshold, and th e mean area with suprathreshold stimulation were determined. Heterotopic no ciceptive stimulation was investigated by the cold-presser test (CPT). Duri ng and immediately after the CPT, the subjective pain threshold, pain toler ance, and mean RIII area were determined again. The same examinations were repeated during hypnosis. Hypnosis significantly reduced the subjective pai n perception and the nociceptive flexion reflex. It also increased pain tol erance and reduced pain perception and the nociceptive reflex during the CP T. These effects were found only in highly susceptible subjects. However, t he DNIC's activity was less evident during hypnosis than during the CPT eff ects without hypnosis. Both hypnosis and DNICs were able to modify the perc eption of pain. It seems likely that DNICs and hypnosis use the same descen ding inhibitory pathways for the control of pain. The susceptibility of the subject is a critical factor in hypnotically induced analgesia. (C) 2000 E lsevier Science Inc. All rights reserved.