Neurons that subserve the sensory-discriminative aspects of pain

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Abstract
Evidence is reviewed that various types of peripheral and central neurons participate in sensory-discriminative aspects of pain. Some types of neurons receive support from 3 or more lines of evidence and hence there is sufficient or nearly sufficient evidence that they are part of a pain sensory system. These include A.delta. heat nociceptive afferents, C polymodal nociceptive afferents, spinal cord wide dynamic range neurons and spinal cord nociceptive-specific neurons. Several other types of peripheral and central neurons are also implicated in pain but with less support, especially those at brain stem, thalamus and cortical levels. Future experiments utilizing these lines of evidence should be important in deciding whether given types of brain stem reticular formation, thalamic and cortical neurons participate in pain discrimination. This analysis points out that classification of neurons based on the stimulus energy which produces threshold activation or on that which produces maximum excitation can be misleading. The present analysis also indicates that one cannot easily label central neurons or pathways in terms of presumed sensations they elicit. The lines of evidence proposed here to implicate neurons in the sensory-discriminative aspects of pain clearly need to be applied to brain stem reticular formation, thalamic and cortical neurons. Pain may be controlled in part by manipulation of the motivational-affective component of pain. These pain control methods, whether psychological, pharmacological, or surgical, which modify pain affect, also are likely to alter other aspects of human behavior and experience.