SEQUENCE OF EVENTS FOLLOWING SYNAPTIC AND ELECTRICAL EXCITATION OF PYRAMIDAL NEURONS OF THE MOTOR CORTEX

Abstract

In cats under local or chloralose anesthesia, responses to thalamic stimulation were recorded from the ipsilateral bulbar pyramidal tract. Four kinds of responses: short-latency, augmenting, recruiting and late, were distinguished according to their temporal characteristics and the sites of stimulation from which they could be elicited. Changes in amplitude and shifts in latency of these potentials were analyzed, while applying conditioning and testing stimuli at different locations and at various stimulus intervals. It is postulated that each synaptic or direct excitation of pyramidal neurons triggered discharges which were followed by a phase of depression (due to inhibition or release of facilitation). Augmenting and recruiting pyramidal responses may be interpreted as the result of direct or indirect disinhibition, and late responses as a spontaneous post-inhibitory rebound.