TONIC AND KINETIC RESPONSES OF CAT'S VESTIBULAR NEURONS TO HORIZONTAL ANGULAR ACCELERATION

Abstract

Single neuronal discharges in the vestibular nuclei were recorded in decerebrate and unanesthetized cats with glass or tungsten microelectrodes. Constant angular accelerations were applied in a horizontal plane for a protracted period of time as an adequate labyrinthine stimulus. The discharge frequency of so-called type-I vestibular neurons showed exponential increase in response to ipsilateral angular acceleration and maintained the increased frequency at a constant level without any sign of adaptation during acceleration. This constant level of maximum frequency was proportional to the logarithm of the acceleration applied. The constants of the equations for these frequency responses of single vestibular neurons were determined. These values were found to be significantly divided into 2 groups, suggesting the existence of 2 kinds of neuron in the vestibular nuclei. The kinetic neurons were characterized by lack of spontaneous discharges, high thresholds for frequency increase, rapid time-course of frequency changes and steep gradient of acceleration-frequency relations. These characteristics were completely inverted in the tonic neurons.