Cochlear microphonics: a comparison between scalp recording vs. intracanalicular recording procedure using tone-burst and click stimuli

Abstract

Abstract Background This study aims to evaluate the effectiveness of recording cochlear microphonics (CM) using auditory brainstem response (ABR) protocols by comparing them with those obtained using electrocochleography (ECochG) protocols. To achieve this objective, 30 healthy participants aged 15–25 years were recruited. CM recordings were recorded using both ABR and ECochG protocols, utilizing three different stimuli (500-Hz tone burst (10 ms & 18 ms) and a 0.1-ms click), each presented at 100-dB SPL through insert earphones. In the ABR protocol, the non-inverting electrode was placed on the mastoid of the test ear, while in the ECochG protocol, a TipTrode was inserted inside the ear canal. The inverting electrode was placed on the mastoid of the non-test ear, and the ground electrode was positioned on the upper forehead for both protocols. The amplitude and onset latency of the recorded CM were then analyzed. Results The study found that CM was detectable in 100% of subjects in both ABR and ECochG protocols when 500-Hz tone bursts were utilized. However, CM was recorded in 86.7% of ears using click stimuli in the ECochG protocol and in 80% of ears using the ABR protocol. The CM amplitude recorded with the ECochG protocol was significantly higher than that recorded with the ABR protocol. Additionally, CM amplitude elicited by tone bursts was significantly higher than that evoked by click stimuli in both protocols. The onset latency of CM evoked by click stimuli showed no significant differences between both protocols. However, the onset latency of CM evoked by 500-Hz tone bursts recorded via the ECochG protocol was significantly earlier compared to that recorded via the ABR protocol. Conclusion The findings of the study suggest that the CM could be recorded using the scalp electrode with ABR protocol also, and this could lead to a cost- and time-effective procedure where audiologists can simultaneously record both cochlear potentials and neural responses. Findings also demonstrate that these recordings could be optimized and more reliably detected across subjects using 500-Hz tone bursts. These insights can guide clinical and research applications in auditory diagnostics and assessments.