Response of thalamic neurons to thermal stimulation of the tongue.

Abstract

Extracellular discharges were recorded from single neurons in the ventrobasal complex of squirrel monkeys (Salmiri sciureus). T+M [thermal and mechanical] units responded to both thermal and mechanical stimulation and T [thermal] units, only to thermal stimuli of the tongue. All T and a small percentage of T+M units displayed sustained discharge rates which were a function of temperatures held constant over a range of 45 =15[degree] C. For both unit types rapid tongue cooling from a 35[degree] standard produced an increased rate of firing. The frequency of the initial discharge of T+M units was proportional to the magnitude of the stimulus change down to 17[degree] C, whereas T units had non-monotonic functions characterized by a "best temperature" within a range of 31-21[degree] C. Temperature changes in the warm direction depressed the ongoing activity. No increase in rate of discharge was ever observed in warming the tongue. T units were higher sensitive to rapid cooling (less than 2[degree] C) from various pre-adapting temperatures (45, 39, 35, 29 and 25[degree] C). T+M units were least sensitive at warm adapting temperatures (12[degree] at 45[degree] C) and not as sensitive as T units at cooler preadapting temperatures (4[degree] at 25[degree] C).