HYPNOTIC HYPOALGESIA AND HYPERALGESIA - DIVERGENT EFFECTS ON PAIN RATINGS AND PAIN-RELATED CEREBRAL POTENTIALS

Pain ratings and pain-related cerebral potentials in response to noxio us stimuli were investigated under hypnotic hypo- or hyperalgesia. Out of a sample of 50 subjects the 10 most highly hypnotizable were selec ted using the Stanford Hypnotic Susceptibility Scale. Phasic pain was induced by brief electrical stimuli intracutaneously applied to the su bject's left middle finger. The subjects took part in three experiment al sessions. The first session was without hypnosis for familiarizatio n with the experimental surroundings. In the two other sessions, the s ubjects were hypnotized and given a suggestion of analgesia or hyperal gesia with respect to pain sensation in the left hand. The sequence of hypnosis was matched within and between sessions. Pain ratings and la te cerebral somatosensory evoked potentials (SEP) were used to quantif y pain reactions. In addition, auditory evoked potentials (AEP) and sp ontaneous EEG were evaluated to differentiate between pain-specific an d unspecific effects of hypnosis. Only the subjects' verbal reports of pain were drastically influenced by hypnosis: suggestion of analgesia diminished the mean pain ratings, suggestion of hyperalgesia enhanced them (P < 0.001). In contrast, the amplitudes of the late somatosenso ry potentials evoked by the pain-inducing stimuli were not modified in either of the suggestive states. Furthermore, no effects of hypnosis were found on AEPs and on the power spectra of the spontaneous EEG. Th e results are discussed on the basis of a dissociation of sensory and affective components of pain under hypnosis.