Cortically induced rhythmic activities in the thalamic ventrolateral nucleus of the cat

Abstract

The effect of stimulation of the anterior sigmoid gyrus on the thalamic ventrolateral nucleus (VL) was studied by recording both focal VL potentials and by intracellular activity from VL relay neurons in locally anesthetized immobilized cats, with spinal cord transection at C2 level. Single stimuli applied to the cortex evoked a sequence of negative and positive waves in VL. When double shocks were applied the short-latency negative potential evoked by the second shock was successively potentiated and depressed coincidently with the negative and positive waves induced by the first shock. The response of VL relay neurons consisted of a short-latency spike evoked antidromically or orthodromically, followed by a prolonged IPSP undergoing rhythmic changes similar to those seen in the cortically induced VL focal potential. When double shocks were applied to the cortex, the IPSP evoked by the second shock did not exceed the peak of the IPSP evoked by the first shock. At certain intervals, the second shock evoked a short-latency depolarizing wave, the nature of which was inferred to be an EPSP.