Effect of direct and transcallosal stimulation on inhibition of unit activity in the cat association cortex

Abstract

Inhibition of association cortical neurons (in the form of inhibition of spontaneous activity or of IPSPs) during direct and transcallosal stimulation was studied in cats immobilized with muscle relaxants. The duration of inhibition of stimulation and the number of stimuli. With an increase in the strength of stimulation inhibition deepened to a certain level for a particular neuron, after which it could be further lengthened with an increase in the number of stimuli. In the case of repeated stimulation by volleys of stimuli, very prolonged inhibition developed gradually in the neurons, during which spontaneous activity was inhibited for 2–5 sec. The duration of the IPSP depended on the intensity of stimulation and number of stimuli and its amplitude depended on the intensity and frequency of stimulation and on the number of stimuli. In some cases the amplitude of the IPSP continued to rise after a short volley of stimuli, even after the end of stimulation. An increase in the number of stimuli in the volley lengthened the IPSPs, but their amplitude remained constant throughout the period of stimulation. Prolonged inhibition (up to a few seconds) was connected with the development of a hyperpolarization postsynaptic potential in the neurons. It is suggested that neurons exerting a monosynaptic inhibitory influence on cells of the association cortex may be located in the opposite hemisphere.