A technique for rapid, reliable assessment of thermal-pain threshold in humans

A simple and reliable method of assessing pain threshold in humans may be useful in a number of research areas, such as in examining acute antinociceptive effects of drugs. We have developed a low-cost, computer-controlled method to reliably assess thermal-pain threshold using radiant heat focused from a slide projector and applied to a small area of skin. An electronic shutter is attached to the projector opening to provide precise onset and offset of heat. A computer keypad allows for subject response at the point of pain onset (i.e., threshold), with latency to threshold determined by computer timer. The details of the apparatus setup, subject preparation, and instructions to subjects are presented. The development of the method is described, and sources of unreliability are identified. Coefficients of variation (CVs) are calculated to provide a measure of variability within subjects across trial exposures and across sessions. Results indicate that the method is reliable for determining pain threshold, especially within sessions, and can be employed with relatively minimal expense and subject preparation.