Magnetoencephalography monitoring of hypnosis-induced modulation of event-related brain responses by hypnosis.

Hypnosis is increasingly used in a medical context. However, the hypnotic process is dynamic, and we currently lack specific and reliable biomarkers to diagnose and rigorously monitor the patient's response to hypnotic suggestions. Here, we aimed to identify physiological biomarkers by investigating cerebral event-related responses in an oddball paradigm using a magnetoencephalography-based method. Twenty volunteers with different suggestibility levels were exposed to standard and deviant sounds as part of an oddball paradigm. Subjects were monitored in three distinct conditions: critical consciousness, while distracted by listening to a story, and during hypnotic trance. In each condition, event-related responses were analyzed in both a source space (auditory cortex and dorsal anterior cingulate cortex) and a sensor space in a minimalistic scenario (two sensors). The statistical analysis revealed significant reductions in amplitudes in the auditory cortex and in sensor measurements during hypnotic trance and distraction relative to critical consciousness. These reductions in amplitudes were observed for both standard and deviant stimuli, regardless of the level of hypnotic suggestibility. In particular, this study aimed to determine whether auditory responses are reduced even without explicit suggestions of induced deafness. A more subtle, but nevertheless statistically significant, difference was also found between the distraction and the hypnotic conditions in the source space. The modulation of the cortical response to auditory stimuli during hypnosis could be used as a physiological marker of the hypnotic process. Hypnotic trance and distraction do not appear to differ significantly, as both seem to induce a similar alteration of critical consciousness.