Electrocochleography (ECochG) with a non-invasive tympanic membrane (TM) electrode in normally - hearing subjects

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Background: Cochlear microphonics (CMs) may play an important role in the diagnosis of auditory neuropathy/dyssynchrony spectrum disorder (ANSD), in the prognosis of cochlear implant (CI) outcome and in the preservation of residual hearing in cochlear implantation. Due to a wide variety of parameter settings, there is a lack of data for non-invasive tympanic membrane (TM) electrocochleography (ECochG) with the current setup and hardware. Purpose: The aim of the study was to determine the optimal parameter settings for the recordings of CMs and to obtain reference data for the summating potentials (SPs), action potentials (APs) and CMs recorded by non-invasive ECochG with TM electrodes in normal-hearing adult subjects. Methods: A total of 24 normal-hearing subjects (right ear pure tone thresholds ≤ 20 dBnHL) aged between 20 and 32 years (10 males and 14 females) were tested. SPs and APs were elicited by a click at 90 dBnHL. CMs were elicited by a click at 100 dBnHL or by a tone burst (2,000 Hz) or broadband (BB) chirp, both at 80 dBnHL. Results: CMs occurred for 100% of clicks, for 79% of tone bursts and for 63% of BB chirps. The click stimulus elicited significantly larger CM amplitudes than the tone burst and BB chirp did. CM amplitudes evoked by tone bursts and BB chirps did not differ from each other. High-pass filter (HPF) settings did not significantly change the CM recordings. There was no relationship between the parameter settings and both, CM latency and duration. Conclusions: The present study provides reference SP, AP and CM values for TM ECochG. It is recommended to use a click for elicitation of CMs with an HPF setting of 100 Hz.
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