Use of an Extra-Tympanic Membrane Electrode to Record Cochlear Microphonics with Click, Tone Burst and Chirp Stimuli

Laura M Coraci,Andy J Beynon

doi:10.3390/audiolres11010010

Laura M Coraci, Andy J Beynon

Open Access

https://doi.org/10.3390/audiolres11010010

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Abstract

This study determined electrocochleography (ECochG) parameter settings to obtain cochlear microphonics (CM) with less invasive flexible extra-tympanic membrane electrodes. In 24 adult normal-hearing subjects, CMs were elicited by presenting click stimuli at 100 dBnHL, tone bursts (2 kHz) and broadband (BB) CE-chirps® LS (Interacoustics, Middelfart, Denmark), both at 80 dBnHL. Different high-pass filters (HPFs) (3.3 Hz and 100 Hz, respectively) were used to investigate response quality of the CM. CMs were successfully obtained in 92–100% with click-, 75–83% with 2 kHz tone burst- and 58–63% with CE-chirp®-LS stimuli. Click stimuli elicited significantly larger CM amplitudes compared to 2 kHz tone bursts and BB CE-chirp® LS (Interacoustics, Middelfart, Denmark). No significant differences were found between the two different high-pass filter (HPF) settings. The present study shows that it is possible to obtain clear CMs with the flexible extra-tympanic membrane electrodes using click stimuli. In contrast to 2 kHz tone bursts and CE-chirp® (Interacoustics, Middelfart, Denmark) LS, clicks show a significantly higher success rate and are the preferred stimuli to confirm the presence or absence of CMs.

Highlights

The purpose of this study was to investigate the feasibility of using flexible silicon ET membrane electrodes instead of relatively invasive TT needle electrodes to obtain cochlear microphonic (CM)
This is the first study that explicitly describes the recording of CMs obtained with a flexible silicon tympanic membrane (TM) electrode comparing clicks, 2 kHz tone bursts and CE-chirp® LS stimuli
In addition to analyzing and proposing the most optimal stimulus parameter settings with respect to the different stimulus types, the high-pass filters (HPFs) recording parameter was analyzed for two different HPF settings during CM acquisition

Summary

Introduction

Auditory evoked potentials (AEPs) from the cochlea and the auditory nerve can be assessed objectively by electrocochleography (ECochG), revealing four basic components within the first 5 ms after stimulus onset: (1) the compound action potential (AP), which can be described as a reflection of the combined firing of thousands of cochlear nerve fibers and can be clinically interpreted as a measure of the actual auditory response or “hearing potential”; (2) the summating potential (SP), which reflects the nonlinear distortion from the outer hair cells (OHCs) [1]; (3) the auditory nerve neurophonic (ANN), reflecting the auditory nerve firing most likely to occur as a response to low frequency tones [2]; and (4) the cochlear microphonic (CM), which is a preneural reproduction of the acoustic signal that “mirrors” the movement of the basilar membrane, reflecting the spatial summation of transducer currents produced by a large number of OHCs [3]. The development of computer averaging algorithms enabled the first nonsurgical ECochG recordings under local anesthesia [5]. This transtympanic (TT) ECochG is a rather invasive procedure, requiring an insertion and middle-ear placement of a needle recording electrode through the tympanic membrane, usually carried out by a surgeon. For the diagnosis, evaluation or prognosis of hearing losses in specific patient groups, such as Meniere’s Disease (calculating the ratio between the SP and compound AP as an indicator for endolymphatic hydrops), ECochG was still applied [6]

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