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“No pain sensation”at the left, lower end, and by“Most intense pain sensation


imaginable”at the right end for the pain intensity rating. The left end is anchored by
“Not at all unpleasant,”and the right end is anchored by“Most unpleasant imagin-


able”for the pain unpleasantness rating. Subjects and patients rate their pain intensity


and unpleasantness independently by placing a mark on the line to rate the pain


intensity (unpleasantness) of their clinical pain and each experimental pain stimulus


presentation. Each rating is scored by measuring the distance in mm from the lower


endpoint to the point at which the mark intersects the line. As before, the VAS ratings


for the experimental pain levels are highly correlated with the stimulus magnitudes,


indicating that the subjects can reliably rate graded levels of experimental pain using


the pain intensity-anchored and unpleasantness-anchored VAS. Figure6.3 provides a


composite representation of results from studies where subjects rated experimental


pain intensity magnitudes with VAS. Furthermore, the clinical pain match points


determined by VAS pain intensity and unpleasantness ratings and the perceptual


match between clinical pain and experimental pain stimuli lie close to the stimulus–


response lines for both pain intensity and unpleasantness ratings, once again indicating


that patients rate the experimental and clinical pains similarly using VAS and


experimental pain ratings predict clinical pain assessment.


How Can Experimental Pain Stimulation be Used to Help


Us Understand Persistent (Chronic) Pain Syndromes?


When we inadvertently touch a hot stove or teakettle (noxious heat≥45 °C), the
resultant sensations give insights into how pain is encoded. Initially, we quickly


withdraw our hand coincident with our perception of a sharp, pricking pain


Fig. 6.3 Visual analogue scale ratings of experimental pain. The group-mean pain intensity visual
analogue scale ratings for each of the seven experimental pain stimuli plotted as functions of the
stimulus magnitudes (representation from multiple studies employing multiple stimulus types).
Each pointrepresents the mean from multiple trials


6 The Challenge of Measuring Pain in Humans 109

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