Recovery cycle of the evoked potential in the thalamic nuclei was investigated in 18 adult cats under moderate chloralose-urethane anesthesia. Both concentric bipolar electrode and glass-insulated tungsten microelectrode were used to record the amplitude of mass response or the number of the unit discharge respectively. Stimuli were applied to the peripheral (radial, tibial, peroneal and sural) nerves in the following three different ways : 1) double shocks to a nerve in a extremity, 2) two shocks separately to two different nerve trunks in the same extremity, 3) two shocks separately to two different nerve trunks in the different extremities. It was observed that the time course of the recovery cycle became shorter in the following order : 1) recovery tested by the routine double shock method in the same nerve trunk, 2) recovery tested by the stimuli separately applied to the different nerve trunks in the same extremity, 3) recovery tested by stimuli separately applied to the different nerve trunks in the different extremities. Such an order was also found to exist in the absolute refractoriness. This conclusion is schematically illustrated in Fig. 10 of the text. Different degrees of interference between two responses were discussed from the point of view that they might be attributed to the different overlapping density in the termination of sensory neurons at the thalamus where sensory afferents have some aspect of somatotopic alignment. The relatively long absolute refractoriness was also discussed in the text and might be explained by the thalamic recurrent inhibitory neurons which were proposed by Andersen and others (1962), to which the present observation also gave further confirmation (Fig. 9)
