Brainstem Responses to Electrical Stimulation of the Cochlea

We performed a brainstem evoked response (BSER) study to evaluate the extent to which electrical stimulation of the cochlea was conducted centrally by facial, vestibular, and cochlear nerves. Short-term experiments were performed in three monkeys: via a postauricular approach to the round window, a molded Silastic multielectrode prosthesis was placed in the scala tympani. The BSER was recorded to threshold and suprathreshold biphasic electrical pulses delivered to the implant electrodes. A middle cranial fossa dissection was then carried out, exposing the nerves of the internal auditory canal from above. Facial and vestibular neurotomy had no significant effect on BSER, while cochlear nerve section abolished the response. In one animal, blunt pressure on the cochlear nerve caused a reversible loss of electrically evoked BSER. Electrically evoked BSER probably depends on propagated impulses in the cochlear nerve.