Mapping auditory nerve firing density using high-level compound action potentials and high-pass noise masking

Abstract

Future implementation of regenerative treatments for sensorineural hearing loss may be hindered by the lack of diagnostic tools that specify the target(s) within the cochlea and auditory nerve for delivery of therapeutic agents. Recent research has indicated that the amplitude of high-level compound action potentials (CAPs) is a good predictor of overall auditory nerve survival, but does not pinpoint the location of neural damage. A location-specific estimate of nerve pathology may be possible by using a masking paradigm and high-level CAPs to map auditory nerve firing density throughout the cochlea. This initial study in gerbil utilized a high-pass masking paradigm to determine normative ranges for CAP-derived neural firing density functions using broadband chirp stimuli and low-frequency tonebursts, and to determine if cochlear outer hair cell (OHC) pathology alters the distribution of neural firing in the cochlea. Neural firing distributions for moderateintensity (60 dB pSPL) chirps were affected by OHC pathology whereas those derived with high-level (90 dB pSPL) chirps were not. These results suggest that CAP-derived neural firing distributions for high-level chirps may provide an estimate of auditory nerve survival that is independent of OHC pathology.

Constructing a three‐dimensional electrical model of a living cochlear implant user's cochlea

“…In reality, it is known that neural survival comprises both total neural loss in some areas and loss of dendrites in areas where the neurons are still alive . Neural survival in terms of regions where limited or no neurons occur may be estimated from masking experiments , but the present study did not take this into account. Finally, conductivity values of intra‐cochlear and extra‐cochlear structures are currently based mostly on non‐human data, that is, conductivity values for human tissues may differ from these values, which may also affect the predicted potential spread and neural excitation spread.…”

The potential use of low-frequency tones to locate regions of outer hair cell loss

“…Once the animals were sedated and the bulla opened, DPOAEs were collected for baseline and also to determine whether the animals had existing hearing loss. If DPOAE amplitudes were two standard deviations below normative data collected by Earl and Chertoff (2012), the animal was considered hearing impaired and was not used in the study. Healthy animals then received either the control or experimental treatment.…”

Analysis of the cochlear microphonic to a low-frequency tone embedded in filtered noise

“…The use of masking to limit electrophysiologic responses to specific cochlear regions is not unique. Many researchers have used masking and derived band techniques to estimate the cochlear locations contributing to the compound action potential (Teas et al, 1962;Elberling, 1974;Eggermont, 1976;Spoor et al, 1976;Zerlin and Naunton, 1976;Evans and Elberling, 1982;Shore and Nuttall, 1985;Earl and Chertoff, 2012), auditory brain stem response (Klein, 1986;Conijn et al, 1992;Boettcher et al, 1995;Oates and Stapells, 1997a,b), and CM (Ponton et al, 1992).…”