EFFECTS OF INTRAVENOUS INFUSION OF CENTRAL DEPRESSANTS ON THE EVOKED POTENTIALS OF THE AUDITORY CORTEX IN THE CATS

Abstract

Effort toward finding some integrative functions in the cortical projection areas of the auditory systems has been made by several investigators. Raab and Ades (1) have reported that temporary amnesia for the learned habit is founded after bilateral ablation of the auditory cortex, but the habit is readily relearned. On the other hand, Neff et al. (2) have demonstrated that bilateral ablation of auditory cortex in the cat does lead to a lasting deficit in ability to localize sound in space. They have suggested following hypotheses: 1) an intact auditory cortex is necessary in order that the relationship between auditory signal and food reward may be learned, 2) an intact auditory cortex is essentially for maintenance to attention to an auditory signal, and 3) an intact auditory cortex is necessary for accurate localization of sound in space. However, the results have failed clearly to single out any of these. Lilly (3) and Lilly and Cherry (4) have shown the patterns of spontaneous electrical activity and those evoked by acoustic stimulation in the auditory cortex of the cat by means of a recording technique which gives simultaneous samples of the electrical activity from 25 electrodes on the cerebral cortex. From the observations under light and deep anesthesia, they have demonstrated that there is a certain validity to the accepted subdivision of auditory cortex, although this may have been overplayed in the past because most workers have used deeply anesthetized animals as the standard preparation. Effects of anesthetics on the spontaneous activity and the evoked responses in the auditory cortex have also been shown by Reinberger and jasper (5), Brazier (6), Kiang et al. (7) and Pradhan and Galambos (8). It is generally known that most of anesthetics or hypnotics produce behavioral excitement in the induction phase. However, there is scarcely any systematic study for the relationship between the cerebral acoustic activity and infused doses of the anesthetics. The present experiments were designed to observe the effects of the central depressants continuously and intravenously infused on the spontaneous electrical activity and the response of the auditory cortex to acoustic stimuli in order to analyze the cortical or subcortical mechanism of hearing.