Rebound excitation and the rhythmic activity of the ventrobasal complex of the thalamus.

(1) Membrane potential changes of 18 thalamocortical relay (TCR) cells of the ventrobasal complex of the cat thalamus were recorded intracellularly during rhythmic thalamic activities under moderate barbiturate anesthesia. (2) A single cutaneous stimulus evoked an initial EPSP followed by a longlasting IPSP. On the late declining phase of the IPSP, clustered rapidly rising depolarizations (RDs) were seen to generate a burst of spike potentials. The cluster of depolarizations was often followed by an IPSP, and another cycle of IPSPs and RDs with bursts of spikes was repeated. Similar rhythmic activities of TCR cells and clusters of RDs were also evoked by a single cortical stimulus, Spontaneous occurence of RDs was observed. (3) The temporal correlation between the occurrence of RDs and that of the spike potentials was noted. (4) Chloride ions were injected into the TCR cell through the recording microelectrode to eliminate the membrane hyperpolarization which would initiate the postanodal exaltation. After inversion of the IPSPs, RDs remained in the similar phase of rebound excitation to that before the reversal of the IPSPs. (5) it is concluded that excitatory inputs to TCR cells play an important role for the generation of the rhythmic discharges of TCR cells.