Spatial Summation of Pain

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Abstract
Spatial summation for pain was investigated using three different approaches. A total of 162 thermal radiation experiments were conducted, using both male and female subjects. Cutaneous pain thresholds were determined on the forehead over areas from 2.5 cm2 to 16 cm2 by recording skin temperatures during exposure to thermal radiation. The spatial summation phenomenon for pain, using a cold stimulus, was studied in 68 experiments by comparing the time and temperature at which pain occurred for the immersion of one hand as compared with immersion of both hands. From oscillographic recordings, determinations were made of the time to pain threshold and the skin temperature at pain threshold, as measured by 40-gauge copper-constantan thermocouples attached to the base of the index finger. A cutaneous needle scratch method was employed in a series of 18 experiments on three subjects. The movements of the stimulator arm as it progressed over the skin were recorded on a kymograph. The results indicate that there is a limited, but significant amount of spatial summation for pain with the thermal radiation technique. No statistically significant spatial summation for aching pain could be demonstrated upon stimulation of both hands by the cold immersion technique. The needle scratch method produced inconclusive results as to the presence of spatial summation of pain due to overlap of separate spatial and temporal effects. Submitted on May 1, 1958