Evaluation of the Interest of Hypno-relaxation During Somatosensory Evoked Potentials

Somatosensory evoked potentials corresponds to a neurophysiological exam that studies the functioning of the sensitivity pathways. It is often complementary to the imaging examination (MRI or scanner) and the electroneuromyogram which studies only the peripheral part of the sensory and motor pathways while the somatosensory evoked potentials are interested in their central and peripheral component.

The studied information are the potentials generated in the nervous system by the presentation of sensory stimulation. The examination makes it possible to study conduction times which will be defined as normal or pathological according to standards established on control subjects. Their indication is multiple: study of the repercussions of cervical osteoarthritis, specify the diagnosis of certain neuropathies, study of the conduction pathways at the medullary level in the event of trauma or inflammatory or other lesion.

In our study, the investigators will only be interested in the somatosensory evoked Potentials.

A study has shown that hypnotic suggestions to reduce the unpleasantness of pain triggered by thermal stimulation lead to a selective reduction of activity in the anterior cingulate cortex without modifying the activation of the somesthetic cortex.

Pain is, like all sensory stimulation, subject to the influences of attention, anticipation, mental imagery, previous conditioning. The fronto-cingular areas, activated by analgesics such as morphine, or by cortical stimulation are the same as those used by non-drug techniques such as hypnosis.

Therapeutic hypnosis is "a relational experience bringing into play physiological and psychological mechanisms allowing the individual to live better, reduce or eliminate an acute or chronic painful pathology" (Definition of Doctor Jean Marc Benhaiem).

The study of somatosensory evoked Potentials is a long examination (90 to 120 minutes), which can be uncomfortable for the patient (patient lying down, immobile and relaxed), not having to contract his muscles, especially if he is already painful due to his pathology or if it is difficult for him to remain motionless in the supine position. It is indeed necessary to average around 600 to 1000 responses (number of averages) to a small electrical simulation on each member studied.

The muscular contractions of an anxious and/or painful patient prolong the duration of the examination or even disturb the results, to the point of making it impossible to interpret the examination.

To our knowledge, hypnosis has already been used to improve muscle relaxation and reduce anxiety and pain during electromyograms, but hypnosis has never been used to improve the outcome of somatosensory evoked Potentials. Furthermore, if hypnosis modifies certain late cortical waves, it does not cause modification of the early waves and therefore does not disturb the results expected in our clinical practice.