Abstract

EEG and oscillographic tracings of evoked electrical activity were recorded from the surface of the isolated and surrounding intact cerebral cortex in unanesthetized dogs. Activity was evoked by the topical application of stimulant drugs or by single electrical shocks applied directly to the isolated cortex. Electrical field potentials also were recorded from various depths of the isolated cortical region with a fine wire electrode. The patterns of evoked potentials in the isolated cortex were less complex than those which occurred in intact regions.

Topical application of GABA or its beta-hydroxy analogue to cortical regions "reversed" surface negative spikes due to strychnine, d-tubocurarine, pentylenetetrazol, or picrotoxin. "Reversal" by GABA of surface and deep electrical activity compared with that by local anesthetics and techniques of injury indicated that additional factors besides volume conduction may be involved in the alteration of these spikes. The "dendritic" response, evoked by single electrical shocks to the isolated gyrus, was reversed only in the superficial layers by the application of 0.1% GABA. A concentration of 0.5% GABA, however, reversed the negative wave recorded from deeper layers as well.