Cerebral and Autonomic Responses to Pain in Healthy Humans

Evaluating the intraoperative pain is a major challenge for the anesthesia team. During anesthesia, changes in heart rate and blood pressure are interpreted qualitatively to evaluate the sympathetic response to nociceptive stimulation or the adaptation of analgesia during surgery. The new nociception monitors under development quantitatively explore other variables dependent on sympathetic activity or sympathetic / parasympathetic balance, such as the pulse wave amplitude measurement (Surgical Pleth Index (SPI index)), the pupil dilation reflex, respiratory sinus arrhythmia (ANI, Analgesia Nociception Index), or skin conductance index. Taken independently, these tools provide an assessment of nociception based on variations in the autonomic system, more robust than simply observing heart rate or blood pressure raw values. However, the relationship between variations in the neurovegetative system and pain can be compromised by various factors or intraoperative events such as hypovolemia, bleeding, certain sympathomimetic or sympatholytic treatments, the hypnosis depth, ventilation variation, fast filling, or body temperature. Moreover, investigators do not know the delay between the application of the painful stimulus and the observation of the variation of the different neurovegetative variables. This constitutes a limit of the practitioners' confidence in these monitoring tools. The nociception transmission pathways of to the vegetative centers and cortical areas are complex. Investigators hypothesis is that neurovegetative variations in response to nociceptive stimulation are not always associated with a cortical somatosensory response. In this project investigators investigate the relation between cortical (EEG) and vegetative reactions to acute and tonic nociceptive stimuli, as a preliminary step to apply these procedures to assess intraoperative reactions to nociceptive procedures in anesthetized patients.