Neurophysiologie clinique = Clinical neurophysiology
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In the first part of this report a methodology is described which allows an objective and specific exploration of experimental pain in man by using some electrophysiological features of cutaneous reflexes. This method can be summarized as follows: in normal and trained volunteers, we studied simultaneously the recruitment curves of the nociceptive flexion reflex of a knee-flexor muscle (biceps femoris muscle) and that of pain sensation elicited by electrical stimulation of the ipsilateral sural nerve at the ankle. In this procedure, we found that the reflex threshold (Tr) was closely related to that of pain threshold (Tp) around a similar value (10 mA). ⋯ On the other hand, data also show that the spinal level is one of the main important sites of the mechanisms of morphine-induced analgesia since this drug is found to strongly depress selectively the nociceptive transmission directly at the spinal level. Finally, this method is applied for investigating the nociceptive reactions in patients affected either with a pathological lack of pain sensation or, by contrast, in patients complaining of acute or chronic pain from various origins. Since the nociceptive flexion reflex can be considered as a specific and objective physiological correlate of a pain sensation, it can be successfully employed as a useful tool for investigating some aspects of the human nociceptive reactions in both experimental and pathological situations.