Electrophysiology of the electrically and mechanically damaged cochlea

Electrical and mechanical stimuli were used in an attempt to cause cochlear deafness in a preparation with a rich supply of afferent cochlear neurons. Hearing sensitivity was assessed by electrocochleography and neuron survival was estimated by evaluating electrically induced auditory brainstem responses (EABR). Charge balanced sinusoidal alternating currents between 1 and 30 kHz for up to 15 hours produced a limited high frequency hearing loss when applied through the intact round window. A similar permanent threshold shift (PTS) could be induced by mechanical irritation with a scala tympani electrode through a round window fenestration. There is a summation of electrical and mechanical damage; however, complete deafness never occurred and the EABR provided no evidence for a major retrocochlear damage. These results suggest that deafness associated with perilymph leakage or induced during certain types of ear surgery should not be accepted as inevitable.