Effects of age on temporal summation and habituation of thermal pain: clinical relevance in healthy older and younger adults.

Although the effects of aging on the experience of clinical pain seem relatively clear, investigations of age-related changes in pain perception using laboratory-based pain assessment procedures have yielded contradictory findings. One potential source of variability in this literature is the type of experimental noxious stimulus that is used. Although thermal pain thresholds are the most commonly reported measure of pain sensitivity, use of suprathreshold stimuli in pain assessment procedures may yield additional, more clinically relevant information concerning the effects of aging on the experience of pain. The present study examined the effects of age on temporal summation of both the intensity and unpleasantness of thermal pain at multiple stimulus temperatures. Specifically, responses to repetitive thermal stimuli delivered to the volar forearm at 47 degrees C, 50 degrees C, and 53 degrees C were assessed in 34 younger (mean age, 22.4 years) and 34 older (mean age, 62.2 years) healthy volunteers. Results suggested that for the 47 degrees C and 50 degrees C stimulus trains, older adults exhibited higher ratings of the intensity and unpleasantness of thermal pain and enhanced temporal summation of thermal pain relative to younger adults. Moreover, thermal pain sensitivity was inversely related to perceptions of general health and to reports of recent clinical pain among younger, but not older, subjects. Collectively these findings may indicate small, although potentially significant, age-related alterations in the plasticity of the central nervous system or endogenous pain-modulatory capacities.