A Psychophysical Comparison of Sensory and Affective Responses to Four Modalities of Experimental Pain

Abstract

It is generally accepted that the sensory and affective components of pain may be differentially associated with various acute and chronic diseases, and that some treatment regimens are best directed toward certain aspects of the pain experience. In addition, experimental animal models have been described that presume to assess either the sensory-discriminative aspects of phasic pain or the affective responses associated with tonic pain. The present psychophysical experiment directly compares the perceived intensity and unpleasantness of sensations evoked by four types of experimental noxious stimuli: contact heat, electric shock, ischemic exercise, and cold-pressor pain. A novel pain measurement technique is described that incorporates unbounded magnitude-estimation/category scales; this technique allows precise ratio responses, while minimizing within- and between-subject variability. We observe that, relative to the perceived intensity of the individual stimuli, subjects consistently differentiate among the degrees of unpleasantness evoked by the four stimulus modalities. Ischemic exercise and cold-pressor pain evoke higher estimates of unpleasantness, and thus may better mimic the pain of chronic disease. The relative unpleasantness produced by contact heat is significantly less than that of the other modalities tested, and therefore contact heat stimuli may be ideally suited for assessing sensory-discriminative aspects of pain perception. Possible neurophysiological mechanisms underlying the observed differences in perceived unpleasantness are discussed in relation to the growing body of literature concerning tonic and phasic pain stimuli.

Stability of Pain Measures in a Different Stimuli Context

“…These erance and pain unpleasantness/intensity -even within the same-day measurement were virtually non-existent, which suggests that pain threshold and tolerance measure one aspect of pain (sensory-discriminative), while pain unpleasantness and intensity measure the other (affective-motivational). This is not in accordance with previous findings [25][26] suggesting high correlations between sensory and affective components of pain, especially in experimental settings.…”

Brainstem involvement in the initial response to pain

“…This in line with a relatively constant pain rating during prolonged cold pressor test (Rainville et al, 1992). Similarly, Bromm and Scharein (1982) showed that while pain ratings and evoked potentials did not show any change over time during several sessions of painful electrical stimulation, the GSR showed decreasing responses.…”

“…Since the stimulation period continued for 2 min in both the conditions that were scanned during the first as well as the second minute, it was not possible to assess the pain ratings for the first and second minute of scanning respectively without undue interference with the repeatability. However, the behavioural aspects including pain rating for the different time periods during prolonged cold pressor test stimulation has previously been thoroughly studied (Rainville et al, 1992;Tassorelli et al, 1995).…”

“…The behavioural stimulus duration effects for the cold pressor test, including pain ratings, have thoroughly been studied previously (e.g., Rainville et al, 1992;Tassorelli et al, 1995). These studies show that the pain intensity rating increases from the onset of the stimulation and levels off after approximately 2 min.…”

“…The idea that the brainstem is more involved in the initial pain response may explain habituation of the autonomic responses during tonic pain (Lovallo, 1975) although the subjective pain ratings increase or remain equal (Rainville et al, 1992;Tassorelli et al, 1995). Brain systems involved in the autonomic response during pain should therefore attenuate their activity during prolonged painful stimulation, while other regions participating in the processing of pain intensity and unpleasantness should increase in activity or at least remain equally activated during the prolonged pain.…”