Behavioral measurement of electrical stimulation thresholds for medial geniculate nucleus

Abstract

Detection thresholds for electrical stimulation applied to medial geniculate nucleus (MG) were measured using operant behavioral procedures. Three experimetns were performed to determine the manner in which detection thresholds were influenced by pulse-train stimulation, by pulse-pair stimulation, and by the presence of concurrent acoustic stimulation. Six cats with electrodes permanently implanted in MG were used in these experiments. Detection thresholds for electrical stimulation decreased in the initial sessions of testing but then stabilized, typically showing a slight increase in sensitivity with prolonged testing. The data indicate that threshold values for caudal MG are approximately twice the threshold values for anterior MG. In the first experiment, electrical detection thresholds were determined as a function of the interpulse interval in 10-pulse trains of stimulation. In the second experiment, detection thresholds were determined as a function of the interpulse interval for stimulation presented in pulse-pairs. In both experiments, threshold was lowered by reduction of interpulse interval. The results are discussed in terms of the efficiency of the electrical stimulation, and in terms of the summation of neural excitation. In the third experiment, the effects of concurrent acoustic stimulation on MG detection thresholds were found to be complex. Sometimes effects resembling facilitation or masking were obtained. The results suggest a means of evaluating in the behaving animal the central effects of peripheral stimulation.