Spatial summation of heat pain in males and females

Sex differences in pain sensitivity have been found to vary between conside rable and negligible. It has appeared that the pain stimulation method is c ritical in this context. It was assumed this might be due to the different degrees of spatial summation associated with the different pain stimulus mo dalities. Hence, sex differences were investigated in spatial summation of heat pain in 20 healthy women and 20 healthy men of similar age. Pain thres holds were assessed by a tracking procedure and responses to supra-threshol d pain stimulation by numerical ratings. Heat stimuli were administered by a thermode with contact areas of 1, 3, 6 and 10cm(2). Pain thresholds were significantly higher with smaller areas stimulated than with larger ones. N o significant effect of area was found for the ratings of the supra-thresho ld stimuli, the intensities of which were tailored to the individual pain t hreshold. Consequently, spatial summation of heat pain appeared to result m ainly in a shift of the pain threshold on the ordinate and not a change of slope of the stimulus-response function in the pain range. In neither of th e two pain parameters were there any sex differences. Therefore, the presen t study demonstrated that sex differences in spatial summation of heat pain are unlikely.