Neurophysiology of nociception and pain in the spinal cord.

Our experiments on the primate spinothalamic tract cells are consistent with the traditional view that the spinothalamic tract in primates is the main pathway responsible for pain sensation. However, we have no evidence concerning the possible role of other pathways, either in pain sensation or in the motivational-affective or reflex responses to painful stimuli. At least two different classes of spinothalamic tract cells, the high-threshold and the wide-dynamic-range neurons, appear to be involved in nociception, although they may well play different roles. High-threshold spinothalamic cells seem well suited to signal stimulus location, as well as intensity. Wide-dynamic-range cells can signal intensity, but they are not likely to provide good spatial resolution of stimuli. On the contrary, they are well suited to explain such phenomena as referred pain and pain radiation.