The psychophysical attributes of heat-induced pain and their relationships to neural mechanisms.

During the last two decades there has been a proliferation of studies evaluating the psychophysical and neural attributes of heat-induced pain. Experiments using radiant and contact heat-induced pain have produced different observations thereby broadening our appreciation of the importance of acknowledging how a noxious heat stimulus is delivered; moreover manipulations of stimulus parameters have now provided a foundation for understanding the underlying neural mechanisms of heat-induced pain and their biological significance. The psychophysical attributes of heat-induced pain include highly reliable thresholds for most body regions, minimal adaptation to maintained noxious stimuli, an exquisite sensitivity to small changes in stimulus intensity, slow temporal summation for some types of heat-induced pain (i.e., second pain) but not for others (i.e., first pain), spatial summation---especially for suprathreshold noxious temperatures---and the perceived spread of pain well beyond the actual body area stimulated (i.e., radiation). The present body of information indicates that the pain system is optimally adapted for conveying precise information about intensity, and is less concerned with other stimulus features, such as spatial patterns or boundaries.