Exploring electrode montasges to optimize the non-invasive clinical recording of auditory evoked AP/wave I

In clinical routine, the use of electrocochleography (Ecog) has sparked renewed interest with new less invasive electrodes (gold eartip electrode) to document complex pathological entities such as endocochlear hydrops, auditory neuropathies, cochlear synaptopathy but also monitoring intracranial pressure changes. To minimize variability due to methodological factors, this study aims to compare, in normal-hearing adults (both gender), the compound action potential (AP)/wave I amplitude recorded with earlobe and ear canal electrodes as well as the effect of click polarity (rarefaction vs. condensation).

All electrophysiological tests were collected using a conventional clinical evoked potential measuring system. The results for AP/wave I latency remained relatively stable between the Auditory Brainstem Response (ABR) and Ecog recording protocols, with a trend toward shorter latencies with rarefaction polarity in women. Our findings support the use of the ear canal electrode with both ABR and Ecog protocols; a vertical electrode montage and rarefaction click polarity consistently provide significantly higher amplitudes for AP/wave I in both genders.

While Ecog has long been used for the objective diagnosis and monitoring of endolymphatic hydrops, Ecog can be also used in the diagnosis of auditory neuropathy. Recent findings from animal studies suggest that the emergence of AP/wave I is a sensitive indicator of age-related or noise-induced cochlear synaptic loss (cochlear synaptopathy). It therefore seems essential to have an optimized Ecog protocol for a more sensitive evaluation of the morphology of AP/wave I as indispensable tool to improve understanding of different pathological entities.