Average spectrum of spontaneous activity at the round window modified by sedation, anesthesia and salicylate

Abstract

The electrophysiological signal recorded at the round window of the cochlea reflects sensory and neural activity of the inner ear. Besides acoustically evoked responses, sometimes temporally averaged, which are usual means of functional assessement; recordings obtained in silent conditions and spectrally averaged reflect spontaneous auditory nerve activy as recently demonstrated. In this paper it is shown that averaged spectrum of spontaneous activitty (ASSA) at the round window of guinea pigs, with permanently implanted electrodes, differs in awake versussedated or anesthetized conditions. This casts some doubt upon the hysiological significance of single-unit analyses of spontaneous auditory nerve activity. It is also shown in this paper thatASSA is modified by administration of salicylate even at a dose which does not induce threshold elevation. These observations set ASSA at the round window as a convenient and very sensitive hysiological measure of spontaneous sensory-neural activity and provide much more convincing foundations for phvsiological exploration of tinnitus in animal models