Can auditory brain stem response accurately reflect the cochlear function?

Auditory brain stem response (ABR) and compound action potential (CAP) recordings have been used in animal research to determine hearing sensitivity. Because of the relative ease of testing, the ABR test has been more commonly used in assessing cochlear lesions than the CAP test. The purpose of this experiment is to examine the difference between these two methods in monitoring the dynamic changes in auditory function after cochlear damage and in detecting asymmetric hearing loss due to unilateral cochlear damage. ABR and CAP were measured in two models of cochlear damage: acoustic trauma induced by exposure to a narrowband noise centered at 4 kHz (2,800-5,600 Hz) at 105 dB sound pressure level for 5 h in chinchillas and unilateral cochlear damage induced by surgical destruction of one cochlea in guinea pigs. Cochlear hair cells were quantified after completing the evoked potential testing. In the noise-damaged model, we found different recovery patterns between ABR and CAP. At 1 day after noise exposure, the ABR and CAP assessment revealed a similar level of threshold shifts. However, at 30 days after noise exposure, ABR thresholds displayed an average of 20-dB recovery, whereas CAP thresholds showed no recovery. Notably, the CAP threshold signifies the actual condition of sensory cell pathogenesis in the cochlea because sensory cell death is known to be irreversible in mammals. After unilateral cochlear damage, we found that both CAP and ABR were affected by cross-hearing when testing the damaged ear with the testing stimuli delivered directly into the canal of the damaged ear. When cross-hearing occurred, ABR testing was not able to reveal the presence of cross-hearing because the ABR waveform generated by cross-stimulation was indistinguishable from that generated by the test ear (damaged ear), should the test ear be intact. However, CAP testing can provide a warning sign, since the typical CAP waveform became an ABR-like waveform when cross-hearing occurred. Our study demonstrates two advantages of the CAP test over the ABR test in assessing cochlear lesions: contributing evidence for the occurrence of cross-hearing when subjects have asymmetric hearing loss and providing a better assessment of the progression of cochlear pathogenesis.NEW & NOTEWORTHY Auditory brain stem response (ABR) is more commonly used to evaluate cochlear lesions than cochlear compound action potential (CAP). In a noise-induced cochlear damage model, we found that the reduced CAP and enhanced ABR caused the threshold difference. In a unilateral cochlear destruction model, a shadow curve of the ABR from the contralateral healthy ear masked the hearing loss in the destroyed ear.

Bilateral EABR stimulating mode testing bilateral CI patients refecting binaural integration:a preliminary study.

OBJECTIVE: To analyze binaural integration, we used a new stimulation mode of the electrically evoked auditory brainstem response (EABR), to reflect bilaterally implanted cochlear function. DESIGN: EABR was tested using the following procedure: First, both ears were evaluated separately, with the contralateral speech processor closed (C), followed by another measurement with both processors open (O). Subsequently, the eV latencies and amplitudes were assessed. The Speech, Spatial, and Qualities of Hearing Scale (SSQ), Categories of auditory performance (CAP) and speech intelligibility rating (SIR) scores were used to assess binaural hearing ability subjectively. STUDY SAMPLE: Fifteen subjects with bilateral CI from 1997 to 2018 were recruited, each diagnosed with severe to profound hearing loss. RESULTS: All SSQ scores, except for one, were greater than six (the exception scored 1.3/0.8/1.0). All CAP/SIR scores except one were greater than 6/4 (the exception scored 0/1). All patients exhibited good quality EABR measurements. The open contralateral processor significantly reduced the eV latency while enhancing the eV amplitude compared to monaural stimulation. The objective EABR results were consistent with subjective speech perception and auditory ability assessed using the SSQ scale. CONCLUSION: The EABR accurately reflected auditory pathway maturation and development after CI; thus, reflecting accordance with subjective speech and hearing performances. Furthermore, bilateral CI facilitates binaural integration and auditory brainstem plasticity.

Interfacing Perforated Eardrums with Graphene-Based Membranes for Broadband Hearing Recovery.

Eardrum perforation and associated hearing loss is a global health problem. Grafting perforated eardrum with autologous tissues in clinic can restore low-frequency hearing but often leaves poor recovery of high-frequency hearing. In this study, the potential of incorporating a thin multilayered graphene membrane (MGM) into the eardrum for broadband hearing recovery in rats is examined. The MGM shows good biocompatibility and biostability to promote the growth of eardrum cells in a regulated manner with little sign of tissue rejection and inflammatory response. After three weeks of implantation, the MGM is found to be encapsulated by a thin layer of newly grown tissue on both sides without a significant folded overgrowth that is often seen in natural healing. The perforation is well sealed, and broadband hearing recovery (1-32 kHz) is enabled and maintained for at least 2 months. Mechanical simulations show that the high elastic modulus of MGM and thin thickness of the reconstructed eardrum play a critical role in the recovery of high-frequency hearing. This work demonstrates the promise of the use of MGM as a functional graft for perforated eardrum to recover hearing in the broadband frequency region and suggests a new acoustics-related medical application for graphene-related 2D materials.

Recording of electrocochleography from the facial nerve canal in mice.

BACKGROUND: The ever-expanding arsenal of genetically modified mice has created experimental models for studying various mechanisms of deafness. Electrocochleography (ECochG) is a recording technique of cochlear potentials evoked by sound stimulation, which was widely used to evaluate the cochlear hearing function. However, there is currently a lack of information on long-term recording technology of ECochG in mice. NEW METHOD: We describe in detail the surgical procedure of implanting electrode into the facial nerve canal in C57BL/6J mice for ECochG recording. The results of ECochG recorded by electrode in the facial nerve canal were compared with ECochG guided by electrode on the round window niche. RESULTS: The surgical method of inserting the electrode into the facial nerve canal is relatively simple and can be completed within 15 min. The electrode inserted into the elongated facial nerve canal is stable and close to the auditory nerve trunk, so it is conducive to long-term auditory function monitoring. Hence, the ECochG guided by the electrode from the facial nerve canal can maintain a stable response for more than two weeks. In contrast, the ECochG guided by the electrode in the round window niche can only be maintained for a maximum of 20 min. COMPARISON WITH EXISTING METHODS: In mice, existing recording techniques of ECochG from round window niche is limited by conductive hearing loss due to middle ear effusion or surgical damage. CONCLUSIONS: ECochG recording from the facial nerve canal is suitable for long-term recording in mice. This electrode approach provides a repeatable and reliable measurement of ECochG.