Cerebral mechanisms of hypnotic induction and suggestion

The neural mechanisms underlying hypnotic states and responses to hypnotic suggestions remain largely unknown and, to date, have been studied only wit h indirect methods. Here, the effects of hypnosis and suggestions to alter pain perception were investigated in hypnotizable subjects by using positro n emission tomography (PET) measures of regional cerebral blood flow (rCBF) and electroencephalographic (EEG) measures of brain electrical activity. T he experimental conditions included a restful state (Baseline) followed by hypnotic relaxation alone (Hypnosis) and by hypnotic relaxation with sugges tions for altered pain unpleasantness (Hypnosis-with-Suggestion). During ea ch scan, the left hand was immersed in neutral (35 degrees C) or painfully hot (47 degrees C) water in the first two conditions and in painfully hot w ater in the last condition. Hypnosis was accompanied by significant increas es in both occipital rCBF and delta EEG activity, which were highly correla ted with each other (r = 0.70, p < 0.0001). Peak increases in rCBF were als o observed in the caudal part of the right anterior cingulate sulcus and bi laterally in the inferior frontal gyri. Hypnosis-related decreases in rCBF were found in the right inferior parietal lobule, the left precuneus, and t he posterior cingulate gyrus. Hypnosis-with-suggestions produced additional widespread increases in rCBF in the frontal cortices predominantly on the left side. Moreover, the medial and lateral posterior parietal cortices sho wed suggestion-related increases overlapping partly with regions of hypnosi s-related decreases. Results support a state theory of hypnosis in which oc cipital increases in rCBF and delta activity reflect the alteration of cons ciousness associated with decreased arousal and possible facilitation of vi sual imagery. Frontal increases in rCBF associated with suggestions for alt ered perception might reflect the verbal mediation of the suggestions, work ing memory, and top-down processes involved in the reinterpretation of the perceptual experience. These results provide a new description of the neuro biological basis of hypnosis, demonstrating specific patterns of cerebral a ctivation associated with the hypnotic state and with the processing of hyp notic suggestions.