The Auditory Nerve Overlapped Waveform (ANOW) Detects Small Endolymphatic Manipulations That May Go Undetected by Conventional Measurements.

Jeffery T Lichtenhan,Kaitlyn A Wenrich,Uzma S Wilson,Farah Dubaybo,Choongheon Lee

doi:10.3389/fnins.2017.00405

Jeffery T Lichtenhan, Kaitlyn A Wenrich + Show 3 more

Open Access

https://doi.org/10.3389/fnins.2017.00405

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Abstract

Electrocochleography (ECochG) has been used to assess Ménière's disease, a pathology associated with endolymphatic hydrops and low-frequency sensorineural hearing loss. However, the current ECochG techniques are limited for use at high-frequencies only (≥1 kHz) and cannot be used to assess and understand the low-frequency sensorineural hearing loss in ears with Ménière's disease. In the current study, we use a relatively new ECochG technique to make measurements that originate from afferent auditory nerve fibers in the apical half of the cochlear spiral to assess effects of endolymphatic hydrops in guinea pig ears. These measurements are made from the Auditory Nerve Overlapped Waveform (ANOW). Hydrops was induced with artificial endolymph injections, iontophoretically applied Ca2+ to endolymph, and exposure to 200 Hz tones. The manipulations used in this study were far smaller than those used in previous investigations on hydrops. In response to all hydropic manipulations, ANOW amplitude to moderate level stimuli was markedly reduced but conventional ECochG measurements of compound action potential thresholds were unaffected (i.e., a less than 2 dB threshold shift). Given the origin of the ANOW, changes in ANOW amplitude likely reflect acute volume disturbances accumulate in the distensible cochlear apex. These results suggest that the ANOW could be used to advance our ability to identify initial stages of dysfunction in ears with Ménière's disease before the pathology progresses to an extent that can be detected with conventional measures.

Highlights

The Auditory Nerve Overlapped Waveform (ANOW) originates in the apical half of the cochlear spiral from afferent neural fibers tuned to low-frequencies (Lichtenhan et al, 2013, 2014, 2016)
We found that the ANOW is considerably more sensitive to all of these manipulations than traditional objective measures of compound action potential (CAP) thresholds and the endocochlear potential (EP): the amplitude of the ANOW was altered by each manipulation, while there were minimal changes to CAP thresholds or the EP
The volume of artificial endolymph injected in our experiments were up to 16 times smaller than those used in previous contemporary experiments to create endolymphatic hydrops that was detectable by conventional CAP threshold measures (e.g., Sirjani et al, 2004)

Summary

Introduction

The Auditory Nerve Overlapped Waveform (ANOW) originates in the apical half of the cochlear spiral from afferent neural fibers tuned to low-frequencies (Lichtenhan et al, 2013, 2014, 2016). The ANOW technique advanced the work done with the auditory nerve neurophonic, which is a cochlear response evoked from low-frequency tones (Henry, 1995; Choudhury et al, 2012; Verschooten et al, 2012; Forgues et al, 2014; Verschooten and Joris, 2014; Koka et al, 2017). Lichtenhan et al (2014) identified when the origin of the cochlear responses to low-frequency tones is, and is not, neural excitation from the apical cochlear half when stimulus level and recording location are varied

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