Thermal sensory decision theory indices and pain threshold in chronic pain patients and healthy volunteers.

Fifty-five low back pain patients and 47 healthy volunteers judged the intensity of calibrated thermal stimuli. The method of constant stimuli yielded a pain threshold, and sensory decision theory (SDT) methods provided two independent indices of perceptual performance: discriminability, P(A), the ability to differentiate among various stimulus intensities; and report criterion, B, the tendency to use a particular response. Compared to healthy volunteers, chronic pain patients were far poorer discriminators [lower P(A)]. In addition, the chronic pain patients were more stoical (higher B) and had higher thresholds for reporting both very faint pain and pain. The poor discriminability in patients could be due to attenuation of afferent neural input. The higher criterion suggests that the thermal stimuli were perceived as being innocuous relative to their clinical pain. Comparison of SDT indices with the threshold measures revealed that the pain threshold was highly correlated to the subject's criterion for reporting pain, B, and unrelated to discriminability, P(A).