The aim of my research project is to study the mechanisms by which psychological factors can modify spinal activity induced by nociceptive stimuli. It is indeed acknowledged that dysregulation of the pain descending modulatory system as well as sensitization of spinal excitability could be involved in the development of chronic pain. More particularly the objective of my project is to study the impact of hypnotic analgesia on somatosensory-induced spinal activity. Two hypnotic suggestion techniques will be used, a first one aiming to suggest a global analgesia of the body, a second one having the capacity to focus analgesia on a restricted part of the body. Neurophysiological makers of the spinal activity will be the N13 component of the somatosensory evoked potentials, indexing ascending transmission of somatosensory inputs, and the RIII component of the nociceptive withdrawal reflexes, indexing local circuitry and motor response of the spinal activity.