EEG correlates of hypnotic susceptibility and hypnotic trance: spectral analysis and coherence.

EEG was recorded monopolarly at frontal (F3, F4), central (C3, C4) and occipital (O1, O2) derivations during A-B-A conditions of waking rest, hypnosis (rest, arm immobilization, mosquito hallucination, hypnotic dream), and waking rest. Stringently screened on several measures of hypnotic susceptibility, 12 very low hypnotizable and 12 very highly hypnotizable, right-handed undergraduate, subjects participated in one session. Evaluations were Fast-Fourier spectral analysis, EEG coherence between selected derivations and maximum spectral power within EEG bands. In eyes open and closed conditions in waking and hypnosis, highly hypnotizable subjects generated substantially more mean theta power than did low hypnotizable subjects at all occipital, central and frontal locations in almost all conditions of waking and hypnosis, with a larger difference in frontal locations. Both low and high hypnotizables showed increased mean theta power in hypnosis, suggesting an intensification of attentional processes and imagery enhancement. Mean alpha power was never a predictor of hypnotic susceptibility. Interactions with hypnotic susceptibility showed that highly susceptible subjects had more beta activity in the left than right hemispheres, while low susceptible subjects showed only weak asymmetry. No main effects for or interactions between waking/hypnosis and hypnotic level were found for coherence between derivations or maximum spectral power within theta, alpha and beta EEG bands.