Electrocochleography in Auditory Neuropathy Related to Mutations in the OTOF or OPA1 Gene

Auditory Neuropathy (AN) is a hearing disorder characterized by disruption of temporal coding of acoustic signals in auditory nerve fibers resulting in the impairment of auditory perceptions that rely on temporal cues. Mutations in several nuclear and mitochondrial genes have been associated to the most well-known forms of AN. Underlying mechanisms include both pre-synaptic and post-synaptic disorders affecting inner hair cell (IHC) depolarization, neurotransmitter release from ribbon synapses, spike initiation in auditory nerve terminals, loss of nerve fibers and impaired conduction, all occurring in the presence of normal physiological measures of outer hair cell (OHC) activities (otoacoustic emissions [OAEs] and cochlear microphonic [CM]). Disordered synchrony of auditory nerve activity has been suggested as the basis of both the profound alterations of auditory brainstem responses (ABRs) and impairment of speech perception. We will review how electrocochleography (ECochG) recordings provide detailed information to help objectively define the sites of auditory neural dysfunction and their effect on inner hair cell receptor summating potential (SP) and compound action potential (CAP), the latter reflecting disorders of ribbon synapses and auditory nerve fibers.