[Lateral asymmetry of the human pain sensitivity.]

In repeated clinical studies a preponderance of pain syndromes on the left side of the body has frequently been observed. Experimental studies in humans revealed a lower pain threshold on the left, nondominant side. On the other hand, some studies do not confirm this lateralization. Since pain threshold is not a very valid measure of pain sensitivity in the range beyond threshold, and since clinical studies are limited by simply counting the incidence of the pain syndromes, we investigated whether a significant lateralization of pain sensitivity exists in the entire range beyond pain threshold. Handedness and gender were included as factors. For experimental pain stimulation in 24 subjects three different methods were used: local pressure on the middle phalanxes, a modified submaximal effort tourniquet test, and submerging the hands into cold water. For pain measurement beyond threshold we used the category splitting procedure (Heller).All three methods of stimulation produced corresponding results. Lefthanded subjects showed decreased pain sensitivity on the left side, right-handed subjects on the right side. This was true for the total range of pain sensitivity. For pain induced by pressure, lateral asymmetry increased with pain intensity, for the other two methods it was constant. Lateral asymmetry was found in all subjects, but significant differences could only be demonstrated in female Ss. It is concluded that both gender and handedness contribute to lateral asymmetry of pain sensitivity in man.