Skin Resistance Changes and Measurements of Pain Threshold.

When the end-point is reached in the HardyWolff method of measuring pain threshold, there is a sharp change in the subjective experience resulting from the stimulus. When the radiation intensity is below the level of the pain threshold, the sensation is one of heat alone. If the pain threshold is exceeded, there is a sensation of heat with an added factor which has been variously described as "a tweak," "a stab of pain," "a pin prick," or "a threat of tissue damage." The usefulness of this technique lies in the fact that however this endpoint is described, it can be duplicated on subsequent trials and after the administration of drugs. The appreciation and description of this endpoint must involve a complex series of neural pathways, including the cerebral cortex. Skin resistance, on the other hand, is primarily under autonomic control, and is only secondarily affected by the cerebrum. Since the stimulus intensity can be adjusted to obtain equal subjective experiences, simultaneous measurements of pain threshold and skin resistance should furnish a means for differentiating between autonomic effects and those involving higher centers. These measurements might be expected to furnish an objective check on the accuracy of the subjective reports, for when the stimulus exceeds the pain threshold, there is a sharp increase in the emotional content of the stimulation and a sudden increase in the magnitude of the skin resistance change would be anticipated. The results obtained from such simultaneous measurements are described in the present report.