(1) Objectives: This study reviews the use of electrocochleography (ECoG) as a tool for assessing the response of the peripheral auditory system and monitoring hearing preservation in the growing population of cochlear implant (CI) users with preserved hearing in the implanted ear. (2) Methods: A search was conducted in PubMed and CINAHL databases up to August 2020 to locate articles related to the ECoG measured during or after the cochlear implant (CI) surgery for monitoring purposes. Non-English articles, animal studies, literature reviews and editorials, case reports, and conference papers were excluded. The quality of studies was evaluated using the National Institute of Health (NIH) “Study Quality Assessment Tool for Case Series Studies”. (3) Results: A total 30 articles were included for the systematic review. A total of 21 articles were intraoperative ECoG studies, while seven articles were postoperative studies. Two studies were conducted ECoG both during and after the surgery. Intraoperative ECoG studies focused on monitoring changes in ECoG response amplitudes during and/or after electrode insertion and predicting the scalar location of the electrode array. Postoperative ECoG studies focused on using the ECoG measurements to estimate behavioral audiometric thresholds and monitor pathophysiological changes related to delayed onset hearing loss postimplant. (4) Conclusions: ECoG is feasible to provide real-time feedback intraoperatively and has a potential clinical value to monitor the status of hearing preservation postoperatively in this CI population with residual acoustic hearing.

Purpose: The middle ear muscle (MEM) reflex is the contraction of the stapedius and tensor tympani muscles in the middle ear cavity in response to loud sound, and relies on a healthy population of auditory nerve fibers. Thus, the MEM reflex can be used as a diagnostic test to quantify auditory nerve survival. This study aims to develop a device to measure the MEM reflex in an animal model, with a long-term goal to develop a biomarker for auditory nerve degeneration. Methods: A source device was constructed using a hearing aid speaker attached to a long and thin tube to create high impedance. A probe consists of a microphone placed near the tip of the tube and the sound source. Sound pressure that reflects the MEM reflex was measured in the probe ear of anesthetized rats while an elicitor stimulus was presented in an opposite ear. Results: The probe to measure the MEM reflex was verified having a constant volume velocity sensitive to changes in sound pressure. Increases in amplitude of sound pressure were apparent when the stimulation signal was presented in the stimulating ear and the amplitude was decreased to baseline when the signal was turned off. After sacrifice of the animal, the reflex was absent. Conclusions: Results showed the feasibility of the probe with high source impedance to measure the MEM reflex in animal ears. Absent reflex after animal sacrifice indicates that the MEM reflex measured using this probe was not an artifact or biological noise.