**3. Neurophysiology and hypnosis**

Hypnotic modulation of suffering provokes changes in the anterior cingulate cortex, leaving primary sensory cortex unaffected. Hypnotic modulation of color perception draining or adding color to a stimulus, real or hallucinated, activates the fusiform color area and the inferior temporal region of cerebral cortex with clearer effects in the left cerebral hemisphere than the right. The activation in the left fusiform area is only affected during hypnosis while the right fusiform activation is affected in both hypnotic and control condition. fMRI (functional magnetic resonance imaging) shows heightened activity in the prefrontal cortex. The hypnotized people produce activity in the visual cortex to hallucinate an image. Hypnotic alteration of perception, involves top-down resetting of the intensity of perceptual response, rather than post perception processing changes. There is a decrease in the activity of the dorsal anterior cingulate (dACC) and an increase in connections between the dorsolateral prefrontal cortex and the insula connections between the dorsolateral prefrontal cortex and the default mode network including medial prefrontal and posterior cingulate cortex also weaken) [9, 10].

Hypnotizability is a stable trait and assessed using scales based on the behavioral response of the person in a social context which is correlated with objective physiological responses. Brain activity and plasticity changes in hypnosis measured by functional magnetic resonance imaging (fMRI), positron-emission-tomography (PET) and electroencephalography (EEG) showed that hypnosis inhibits the reaction of the fear circuitry structures. Frontal and cingulate cortices are most linked to hypnotic responding [11].

Frontal functions have a central role in hypnotic responding. In the first phase of hypnosis, during the induction, the subject's attention on an object stimulates fronto-limbic structures, which are inhibited and/or dissociated in the second phase. In the third phase, right-sided temporo-posterior regions are stimulated. In response to hypnosis, the fronto-cortical activity is reduced and the dorsolateral prefrontal cortex structures are dissociated and the cingulate activity increases or decreases depending on the suggestions. Hypnotic responding demonstrates greater dominance in the right hemisphere than left hemisphere processing, associated with cognitive activities while no difference is found in hypnotizability between left and right hemisphere lesions. *Highs have significantly larger rostrum than lows.* H*ypnosis influences the connectivity between brain regions.* T*he connectivity is decreased between frontal midline areas and left lateral scalp sites in highs while increased between left temporal and right occipital areas in lows.* Areas and type of activity changes in the brain depend on the suggestions, rather than hypnosis per se. Highs are more prone to hypnotic suggestions by higher levels of theta activity and structural connectivity between left and right hemisphere frontal areas. Reducing frontal activity increases the response to hypnotic suggestions and not a general hypnotic responsivity [12–27].
