Electrophysiological Effects of Hypnosis: Topographical and Source Analysis of Hypnotic Paralysis

Archimi, Aurélie

This study focuses on brain mechanisms underlying hypnosis. More precisely, we tested the electrophysiological effects of a specific hypnotic suggestion on brain activity. Theoretical models suggested that hypnosis induces inhibition of frontal executive functions but this hypothesis has never been tested with a task requiring inhibition. To assess modulations of inhibitory process, we used an inhibitory Go/Nogo task involving a motor preparation phase, execution and inhibition phase during EEG recordings in two different contexts, normal context and left-hand paralysis context. The paralysis was either suggested by hypnosis for a group of subjects (N=12) or feigned for another group of subjects (N=12). We first performed topographical analyses on the three different phases to assess the modulations of the electric field in relation to hypnotic suggestion. Our results showed that preparatory activity remained similar in terms of topographies, irrespective of the conditions, which suggests that motor intention was preserved during hypnosis. On the contrary, our results revealed a selective topographical modulation in the time-range of the inhibitory P3 component during the hypnotic suggestion of paralysis. As changes in topographies are linked with changes in the configuration of the generators of activity in the brain, we applied in a second time a source analysis on hypnotic conditions, which showed a significant activity in the right middle frontal gyrus in the time-range of P3 component. These results suggest that frontal executive functions are active during hypnosis, which infirm the inhibition hypothesis and shows on the contrary that subjects under hypnosis are not inhibited but that high-level functions are involved in the hypnotic phenomena. Before to present the theoretical background about hypnosis, we briefly defined what is inhibition and how this latter is traditionally measured with cerebral investigation techniques. We present then how hypnosis has been linked with inhibitory process and finally present the purpose of our study. The results are divided into three parts, representing the different analyses: the behavioral results, the topographical results and the source localization results.

Electrophysiological Effects of Hypnosis: Topographical and Source Analysis of Hypnotic Paralysis

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