Electrocochleography Measures from the Ear Canal of Awake Chinchillas

Disabling hearing loss is a problem around the world, with the World Health Organization estimating that 466 million people worldwide have disabling loss, and that this number is expected to increase to over 900 million people by 2050. There are different types of hearing loss, but sensorineural hearing loss (SNHL) is the most common and results from damage to the inner ear. The audiogram is the most common test used to diagnose hearing loss, but it is limited in that it can only identify a shift in hearing sensitivity (thresholds), i.e., it cannot identify the cochlear location causing SNHL. The electrocochleogram (ECochG) is an evoked response consisting of several summed responses of electrical potentials from within the inner ear. Several components represent activity from different places in the inner ear: the compound action potential (CAP) is the summed onset response of auditory nerve fibers, the cochlear microphonic (CM) is the AC response of the hair cells (primarily outer hair cells), and the summating potential (SP) is the DC hair cell response (primarily inner hair cells). Most ECochG responses in humans are collected non-invasively (e.g., from the ear canal or ear drum), whereas most ECochG responses in animal models are collected invasively (e.g., from the cochlear round window). In this project, we aimed to bridge this gap by recording non-invasive ECochG responses from awake chinchillas. We first started by calculating standard ECochG metrics from existing data across different forms of SNHL. Next, we tested the feasibility of recording non-invasive ECochG responses from the ear canals of awake chinchillas. Finally, we defined and calculated additional metrics from ECochG responses to further help in identifying location(s) of SNHL. The ability demonstrated here to record non-invasive ECochG responses from awake animals increases the translational applicability of pre-clinical SNHL animal models by permitting detailed cochlear assessments at multiple time points post exposure. Detailed ECochG measures can advance hearing science and audiology by helping to identify the location of damage causing the hearing loss, which can ultimately allow for more individualized treatment