The Experimental Approach to Pain

¹ From the Laboratoire de Biophysique, Université de Louvain, Louvair, Belgium

A modification of the Hardy-Wolff-Goodell method of stimulation by thermal radiation was used. Thresholds of pain sensation were obtained in the usual manner but response was measured, not only by the judgment of subjects, but by the reactions in a group of physiological variables as well; these included EEG, EKG, PGR and change in respiration. The threshold values obtained in terms of skin temperatures at stimulus site after irradiation were considerably higher (47.3–48.6°C) than those reported in previous investigations. Differences in threshold skin temperatures at different exposure times imply that the determinant for the sensation is not a critical temperature at skin surface, but is either a critical temperature at receptor level or a temperature difference between receptor level and deeper fibers. Questioning of the subjects reveals that the particular sensation experienced at the ‘pain threshold’ is not painful for the large majority. Consequently, results obtained in threshold investigation can have no applicability to the human pain problem in real life.