DIRECT RESPONSE OF ISOLATED CEREBRAL CORTEX OF CAT

Abstract

The question was: could all DCR (direct cortical response) components seen in intact cortex also be observed in the isolated preparation? Furthermore, the effects of Nembutal (pentabarbital Na), procaine and gamma amino butyric acid (GABA) were investigated since these agents produce striking changes in the DCR of intact cortex. The DCR of acute and chronic isolations did not differ materially, but both had a lower stimulus threshold and higher amplitude as compared with the response from intact cortex. All DCR components of intact cortex (primary negative potential), second negative wave, after-positivity and slow negativity) could be identified in the records from the isolated preparation. However, after-positivity is a much more prominent component in the response of isolated cortex than in the one from intact cortex. In isolated cortex intracortical recording of responses to surface stimuli, as well as surface recording of responses to stimuli applied at varying cortical depths, proved a superficial as well as a deep origin for after-positivity. The effect of I. V. Nembutal on the DCR of isolated cortex differed from that of I.V. Procaine just as in intact cortex. Nembutal depressed the primary potential and second negative wave but augmented slow negativity. Procaine, by contrast, depressed slow negativity, leaving primary potential and second negative wave unchanged. In isolated cortex the effects of surface application of Nembutal (0. 5%) and Procaine (0. 5%) also differed. The action of 05% GABA was found to be similar to that of 0. 5% Nembutal.