Electrodermal Correlates of Hypnosis: Current Developments

Abstract

Hypnosis has proven to be an effective treatment in disorders that affect the autonomic nervous system (ANS). However, the studies investigating the nature of its effect on the ANS have reported contradictory results. Measurement of electrodermal activity (EDA) is an objective way to assess the activity of the sympathetic branch of the ANS. We aim to elucidate the effects of hypnosis on EDA. Here, we report the results of two studies, both investigating the psychophysiological effects of hypnosis.In the first experiment, subjects engaged in an HGSHS:A group hypnosis session to measure their hypnotizability. EDA was measured bilaterally from their wrists. We found a significant reduction in EDA levels and the number of nonspecific responses during the hypnotic induction phase. This effect was observed in all three hypnotizability groups—high, medium, and low hypnotizables. A three-way interaction confirmed that EDA patterns on the left and right sides were characteristically different in these three groups. Left-side dominance was typical in high hypnotizables, whereas low hypnotizables were characteristically right-sided. EDA levels of the two sides remained synchronous in medium hypnotizables. During the suggestion phase, we found significant differences in EDA levels depending on the test suggestions, modulated by hypnotizability. A suggestion, harder to respond to, elicited higher arousal in high hypnotizables as compared to low hypnotizables. In the second experiment, we performed five consecutive hypnosis sessions to confirm the reproducibility of the most prominent effect found in Study 1—a gradual decrease in the level of skin conductance during hypnotic induction. We also confirmed that this effect is independent of the hypnotizability level. We conclude that arousal is bilaterally reduced during hypnosis induction, which is persistent across different levels of hypnotizability. At the same time, lateral differences define unique EDA patterns in the induction phase, characterizing high, medium, and low hypnotizables.