Multiple temperature-sensitive spots innervated by single nerve fibers.

Electrophysiological recordings were made from single nerve fibers which were specifically responsive to temperature changes of the skin of monkeys. Previous reports indicated that the receptive area on the skin of such preparations was a single small spot less than 1 millimeter in diameter. However, we found that the activity in a single thermally sensitive fiber increased when any one of eight individual spots on the skin was cooled. In other preparations two to six spots, each less than 1 millimeter in diameter, appeared to be innervated by a single fiber. The neural activity resulting from the cooling of one or several of these spots summed, and we suggest that this summation may be the neural analog of areal summation of thermal stimuli reported in psychophysical measurements.