A psychophysical analysis of experiential factors that selectively influence the affective dimension of pain

Abstract

A psychophysical analysis was made of experiential factors that influence the affective but not the sensory-discriminative dimension of pain. Seven subjects made cross-modality matching responses to several dimensions of their experience. Before each stimulus, they matched line lengths to their experienced desire to avoid pain (significance) and to their perceived likelihood of avoiding it (expectation). After each stimulus, they matched line lengths to perceived sensation intensity (in some sessions) or to felt magnitudes of positive or negative feeling (in other sessions). Non-noxious (35, 42 degrees C) and noxious (45--51 degrees C) skin temperature stimuli were randomly interspersed during each experimental session. Changes in expectation were induced by preceding one-half of the noxious stimuli with a warning signal. The average responses of these subjects indicated that 45--51 degrees C noxious temperatures were felt as less unpleasant when preceded by a warning signal. In contrast, sensation magnitudes evoked by these same skin temperatures were unaffected by the warning signal. Thus, only the magnitudes of unpleasant responses are lowered by decreasing ones' expectation of avoiding pain. Analysis of individual responses revealed two distinct patterns of response changes following presentation of the warning signal. Four subjects retained the same general goal of avoiding pain and reduced their expectation of avoiding it. Their affective responses were less unpleasant during the warning signal. The remaining three subjects primarily altered their goals and not their expectations on signaled trials. Their affective responses were not modified by the signal. Subjects were instructed to arrive at their affective responses in two ways. In one session, they compared the outcome of each stmulation with what they wanted to happen (affect-result responses). In the other session, they simply focused on the pleasantness or unpleasantness of each sensation as it was experienced (affect-process responses). All subjects' affect-result responses were more positive (or less unpleasant) than affect-process responses. All of these results underscore the critical influence of expectations and the manner in which one evaluates sensations on affective responses to noxious stimulation.

Psychophysical features of the transition from pure heat perception to heat pain perception

“…An inspection of the data presented graphically in several studies on the stimulus/sensation relationship with heat stimuli ranging from nonpainful to painful corroborates this view (Duncan, Bushnell, & Lavigne, 1989;Duncan, Bushnell, Lavigne, Lavoie, & Rivest, 1986 [data presented graphically in Price, 1988J;LaMotte & Campbell, 1978;Price et al, 1980). Straight lines can be fitted to the data quite well until about 45°C-46°C, and also from these temperatures on, but there is a rather abrupt change to a greater slope in this region.…”

“…This suggests that the "pain" exponents reported by Price and coworkers (Price, 1988;Price et al, 1980;Price & Harkins, 1987;Price et al, 1983) were also strongly affected by the slope of the psychophysical function in the heat range. Therefore we think that if true pain parameters are to be derived, the pain threshold must be used as the lower limit of the stimulus range.…”

“…Whereas the significant positive correlations between the slope of OLR and the slopes of TLR above and below the pain threshold are not surprising, the correlations Price et al, 1980;Price & Harkins, 1987;Price et al, 1983), which were around 2.1 and which these authors interpreted as "pain parameters." The fact that the psychophysical functions used by these authors included both the heat range and the heat pain range, as in our study, allows the interpretation that the exponents are not compelling evidence for an expansive stimulus/sensation relationship in the heat pain range.…”

“…They have seemed to yield different results, depending on whether radiation or contact heating techniques have been used (Price, 1988). In a series of studies with radiation heating, Adair and coworkers (Adair, Stevens, & Marks, 1968) found an exponent near unity, whereas in several experiments with contact heating, Price and coworkers (Price, 1988;Price, Barrell, & Gracely, 1980;Price & Harkins, 1987;Price, McGrath, Rafii, & Buckingham, 1983) observed a much more expansive power function with exponents of about 2.1.…”

FMRI Measurement of CNS Responses to Naloxone Infusion and Subsequent Mild Noxious Thermal Stimuli in Healthy Volunteers

“…For unpleasantness, the left end was labeled "not unpleasant" and the right end as "maximum unpleasantness." The difference between pain unpleasantness and pain intensity was explained to subjects prior to experiments using the approach reported previously (Price et al 1980). …”