A decade ago I had occasion to review the problem of pain in an article’ that was not noticed by many neurophysiologists. In looking over more recent literature I was pleased to find that the kind of approach and picture that I then suggested remains essentially valid, despite considerable additions to our knowledge of the pain pathways, chiefly within the central nervous system. The material presented here is based on my earlier review,’ supplemented by a later, more general one,2 and by Sweet’s chapter on pain in the Handbook of Physiology? Other recent reviews are the Ciba Foundation monograph* and Barber’s article in the Psychological Bulletin.6 The lack of real advance in new understanding, including learning how pain emerges into consciousness, is not due to any lack of importance of the subject or of interest in it. I remember well my experiences as an intern at Los Angeles General Hospital, Los Angeles, Calif., over one third of a century ago. We had many Mexican patients, and the only words of Spanish that I learned, I regret to say, were “Donde dueleP,”* which sufficed. The essential point that I shall emphasize, one already alluded to by other contributors to this monograph, is the very real difference between awareness of pain and suffering from it. This distinction is of major importance clinically and pharmacologically, and we are now fairly close to understanding it neurophysiologically. It is possible, on stimulating pain afferents by applying painful stimuli, to produce reflex responses such as changes in skin resistance a t intensities below those required to produce any conscious awareness of them. Conversely, with stronger stimuli or other conditions, one can obtain a perfectly clear awareness of pain and yet not be particularly distressed by it. This condition can be achieved, for example, even with very severe pains, by procedures such as frontal leukotomies or topectomies. The sufferer with causalgic pain and allied ills may remain perfectly aware of feeling severe pain, but may no longer be really distressed by it; probably morphine acts in this manner. Although somewhat debatable, the best evidence I know of indicates that morphine does not raise the threshold of pain receptors to peripheral stimulation. The messages come into the nervous system as before, but they no longer seem as important as formerly. There is, of course, a tremendous variability in the reaction of a given individual to a given painful stimulus, depending upon what can be called, loosely, the internal emotional state and the total external input (aside from the pain stimulus). I suspect that the reader has had the experience of a toothache that seemed insufferable in the forlornness of late night, but became relatively minor the next morning, especially when facing the dentist’s chair. Conversely, in the intense emotion of battle, only about one third of the soldiers who are severely wounded require analgesic medication whereas, in the same age group of males in civilian This variation involves some of the mechanisms that I shall discuss.
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Feb 1, 1971
John P.J Pinel + 2
Open Access