INHIBITION OF BETZ CELL ACTIVITY BY THALAMIC AND CORTICAL STIMULATION

Abstract

Effects were studied of stimulation of the thalamic nucleus ventralis lateralis (VL) on the activity of single cells in the motor cortex of cats with mid-brain lesions. The investigation was limited to those cells which responded antidromically to stimulation of the pyramidal tract. Repetitive stimulation of VL at frequencies up to 30/second resulted in the arrest of the spontaneous activity of these cells for periods as long as 20 seconds following stimulation. The cells remained excitable both orthodromically and antidromically during this silent period and intra-cellular recording revealed no inhibitory effect on the Betz cells themselves. It is concluded that the suppression of spontaneous activity is due to inhibition of other cells in the spontaneously active system. Stimulation of the motor cortex at frequencies up to 15/second resulted in an arrest of spontaneous activity indistinguishable from that produced by stimulation of VL. Cortical stimulation at higher frequencies usually produced after-discharge in the cells,.