Cerebral mechanisms of hypnotic hypoesthesia. An ERP investigation on the expectancy stage of perception

The present study aims at identifying reliable markers of neural preparatory processes during hypnosis. To this goal, we recorded the electroencephalographic activity of 23 volunteers regardless of their hypnotizability score. Somatosensory evoked potentials (SEPs) were elicited while participants received non-painful electrical stimuli on the left median nerve in the conditions of relaxation and hypnosis with suggestions of reduced sensation. SEPs analysis was focused on the pre-stimulus activity and revealed two main components: the prefrontal negativity (pN) and the somatosensory negativity (sN) over the frontal and parietal areas of the scalp, respectively. Results showed reduced amplitudes for both components under hypnosis, mostly for the pN, suggesting a change of top-down control of parietal and prefrontal areas. Furthermore, the sLORETA source imaging showed a deactivation of the lateral and anterior portions of the prefrontal cortex (PFC) during the hypnotic state. The present study highlights the downregulation of the PFC as a core aspect of the adopted hypnotic task and confirms the ability of hypnosis to modulate the activity of frontal executive functions. Further, since the majority of participants fell into the medium range of hypnotizability, the present findings could reflect the hypnosis effects in most of the population.