Differentiation of hypnosis and relaxation by analysis of narrow band theta and alpha frequencies.

Narrow band theta and alpha activity were recorded over anterior and posterior sites before, during, and after hypnosis in high and low hypnotically susceptible subjects (N = 16). In theta, high susceptibles had greater activity posthypnosis, otherwise there were no group differences. These findings common to low and high susceptibles suggest that theta is an index of relaxation that continues after hypnosis in highs. In alpha in high susceptibles, posterior power increased from the prehypnosis to hypnosis conditions and decreased posthypnosis. Exactly the converse effects were seen in lows. Furthermore, highs had greater alpha power than lows during both prehypnosis and hypnosis conditions, demonstrating an association of alpha with hypnotic susceptibility. The results indicate that, whereas theta indexes relaxation, alpha indexes the hypnotic experience and susceptibility.