Effect of hypnosis on masseter EMG recorded during the ‘resting’ and a slightly open jaw posture

Abstract

The aim of this experimental study was to determine whether minimal levels of electromyographic activity in the masseter muscle are altered when individuals are in a verified hypnotic state. Experiments were performed on 17 volunteer subjects (8 male, 9 female) all of whom gave informed consent. The subjects were dentate and had no symptoms of pain or masticatory dysfunction. Surface electromyograms (EMGs) were made from the masseter muscles and quantified by integration following full-wave rectification and averaging. The EMGs were obtained (i) with the mandible in 'resting' posture; (ii) with the mandible voluntarily lowered (but with the lips closed); (iii) during maximum voluntary clenching (MVC). The first two recordings were made before, during and after the subjects were in a hypnotic state. Susceptibility to hypnosis was assessed with Spiegel's eye-roll test, and the existence of the hypnotic state was verified by changes in ventilatory pattern. On average, EMG levels expressed as percentages of MVC were less: (i) when the jaw was deliberately lowered as opposed to being in the postural position: (ii) during hypnosis compared with during the pre- and post-hypnotic periods. However, analysis of variance followed by post hoc tests with multiple comparison corrections (Bonferroni) revealed that only the differences between the level during hypnosis and those before and after hypnosis were statistically significant (P < 0·05). As the level of masseter EMG when the mandible was in 'resting' posture was reduced by hypnosis, it appears that part of that EMG is of biological origin.

Bispectral Index Alterations and Associations With Autonomic Changes During Hypnosis in Trauma Center Researchers: Formative Evaluation Study

“…Although 1 study was performed in France and the other in the United States, the authors reported identical decreases in respiratory rates from 18 to 14 breaths per minute [31,32]. Other hypnosis investigations demonstrated significant reductions in facial EMG measurements in healthy volunteers during hypnosis, as we did in this assessment [33][34][35]. The increases in expired carbon dioxide values and decreases in the respiratory rate and EMG values are consistent with the onset of relaxation during hypnosis.…”

“…Significant reductions in the respiratory rate have been shown to occur with hypnosis [31,32]. Hypnosis has been demonstrated to reduce EMG tension in the masseter, temporalis, and frontalis muscles [33][34][35]. Virtually all studies in the literature that assessed the effects of hypnosis on skin temperature involved volitional efforts to alter the temperature or to mitigate temperature responses to heat or cold stressors.…”