Eighth nerve auditory evoked responses recorded at the base of the vestibular nucleus in the guinea pig

Anatomical and physiological studies of brainstem acoustic nuclei involving the classical ascending auditory pathway or the cerebellar and reticular pathways imply that all afferents from the cochlea terminate in the cochlear nucleus. In the experimental pathology of complete and selective destruction of the cochlea in the guinea pig acoustic responses still evoked at mid and high intensities, demonstrated to come from the saccule, show a pattern of far field evoked brainstem potentials quite different from that of normal animals. Intracranial electrophysiological investigations of the brainstem were undertaken in such pathological animals and in normal guinea pigs for comparison. In both cases acoustic responses were recorded at the base of the vestibular nucleus, showing a first peak corresponding to an eighth nerve projection and after a synaptic delay a second peak of local activation. In normal animals acoustic responses from the vestibular nucleus showing normal threshold and tuning curves may represent a direct projection from the cochlea.