The Efficacy of Hypnosis- and Relaxation-induced Analgesia on Two Dimensions of Pain for Cold Pressor and Electrical Tooth Pulp Stimulation
This study evaluated the efficacy of hypnosis- and relaxation-induced suggestions for analgesia for reducing the strength and unpleasantness dimensions of pain evoked by noxious tooth pulp stimulation and by cold pressor stimulation. The Tellegen Absorption Questionnaire was used to assess hypnotic susceptibility for 28 subjects in order to match treatment groups according to sex and susceptibility scores. Tooth pulp stimulation consisted of a 1 sec train of 1 msec pulses at a frequency of 100 Hz, applied at 20 sec intervals to the central incisor. Six stimuli, selected between subject's pain and tolerance thresholds, were presented 3 times each in random order. Cold pressor stimulation consisted of forearm immersion in a circulating water bath maintained at 0–1°C. Subjects made threshold determinations of pain and tolerance and used Visual Analogue Scales to rate the strength and the unpleasantness of both noxious stimuli before and after receiving either hypnosis- or relaxation-induced analgesia.
There were no significant differences in pain reductions between hypnosis- and relaxation-induced interventions. However, the percent reduction in both strength and unpleasantness varied significantly as a function of the type of pain. Both hypnosis and relaxation significantly reduced the strength and the unpleasantness of tooth pulp stimulation, but only the unpleasantness dimension of cold pressor pain. The pain reductions were not correlated with subjects' hypnotic susceptibility levels.
The results indicate that the extent and the quality of the analgesia produced by these cognitive-based therapies vary not only according to subjects' characteristics and the efficacy of the intervention, but also according to the nature of the noxious stimuli. Tooth pulp and cold pressor stimulation represent qualitatively different stimuli with respect to both the type of nerves activated and the mode of stimulus application. Discrete, randomly presented levels of noxious electrical stimulation to the teeth activate predominantly small fibers and produce brief pain sensations that vary unpredictably in intensity. In contrast, continuous cold stimulation to the forearm activates a variety of nociceptive and non-nociceptive fibers and produces progressive cold and pain sensations with a predictable increase in intensity from cold sensations to paresthesia and severe pain.