Mapping Auditory Nerve Firing Density Using the Compound Action Potential and High-pass Noise Masking By

A critical barrier to future implementation of regenerative treatments for sensorineural hearing loss is the lack of diagnostic tools that can specify the target(s) within the cochlea and auditory nerve for delivery of therapeutic agents. This study used a gerbil model to test the idea of mapping auditory nerve firing density by tracking the amplitude of high-level compound action potentials (CAPs) while varying the bandwidth of simultaneous masking noise. The distributions of neural firing, obtained by calculating the derivative of the equation describing CAP amplitude growth as a function of distance along the cochlea, indicated that high-level chirp stimuli trigger widespread neural firing in the cochlea that is unaltered by sensory outer hair cell pathology. These results suggest that CAP-derived neural density functions for high-level chirp stimuli may provide reliable maps of auditory nerve density in impaired ears.