Surface-evoked cerebral and cerebellar responses were compared in 35 cats. Single stimuli and 1-second trains (6 and 20/sec.) were used. Effects of gamma aminobutyric acid (GAB) applied to the cortical surface and of Nembutal and procaine injected intravenously were studied. Response of cerebral cortex to a single shock shows at least four components: initial negative spike, second negative wave, after-positivity, and slow negativity. Cerebellum shows only the initial negative spike and the slow negativity, second negative and after-positivity components being absent. In both cerebrum and cerebellum slow negativity shows summation with serial stimulation. Application of GAB to the cerebellar surface causes replacement of the negative spike by a positive one and a concurrent reduction in amplitude of slow negativity. In cerebral cortex Nembutal produces a striking augmentation of singly or serially evoked slow negativity, but marked amplitude reduction or reversal to positive polarity of the serially evoked primary spikes. By contrast procaine abolishes summed slow negativity of cerebral cortex leaving serial spikes unaffected. In the cerebellum Nembutal and procaine have no effect upon the direct cortical response at dosage sufficient to produce cerebral alterations. Thus synaptic activity signaled by the responses studied appears to be more susceptible to Nembutal and procaine in cerebrum than in cerebellum.
SLOW AND SPIKE COMPONENTS OF THE DIRECT CORTICAL RESPONSE IN THE CEREBRAL CORTEX
