Cortical Auditory Evoked Potentials Recorded Directly Through the Cochlear Implant in Cochlear Implant Recipients: a Feasibility Study.

OBJECTIVES: The use of objective measures in cochlear implant (CI) mapping, has greatly contributed to the refinement of the setting of audible and comfortable stimulation levels, which serve as the basis of the mapping process, especially in cases of infants and young children. In addition, objective measures can also confirm the integrity of the CI system. Current CI objective measures mainly reflect neural activity from the auditory nerve and brainstem site. An objective cortical CI measure that reflects directly central auditory activity is greatly needed, especially since it is closely related to CI outcomes in both children and adults. Recording the brain activity currently requires an external evoked potential (EP) system including scalp electrodes, rendering it impractical for widespread clinical use. This study aimed to assess the feasibility of recording cortical auditory evoked potentials (CAEPs) directly and solely through the cochlear implant in response to external acoustic stimulation in the non-implanted ear. DESIGN: A total of nine CI users (four females and five males) participated, including seven post-lingual adults (23 to 72 years), and two pediatric cases, one teenager (15 years), and one child (8 years)-both pre-lingual. All participants had a residual hearing in the ear contralateral to the ear with CI. CAEPs were recorded in the implanted ear in response to acoustic stimulation of the non-implanted ear, consisting of a brief tonal stimulus at comfortable listening levels. Recordings used an intracranial montage consisting of an intracochlear apical electrode (active) and one of the two ( case and ring ) extra-cochlear implanted electrodes serving as reference electrodes. The CI CAEPs were compared with a single-channel conventional CAEP recording obtained simultaneously via scalp electrodes (Fz-mastoid) using a standard EP system and an external trigger from the CI system. Statistical comparisons were made between the CI and the scalp recorded CAEPs and for differences between the CI CAEP measures acquired using the ring and the case as the reference electrode. RESULTS: CAEPs recorded directly and solely through the CI were equivalent to the standard scalp recorded CAEP responses. CAEP responses acquired using the case electrode as the reference were highly correlated in terms of morphology, latencies, and amplitudes of the CAEP components. The CI CAEP latencies of the two pediatric cases were consistent with their normal developed age group and delayed relative to adult CAEP latencies, as expected. CONCLUSIONS: This study demonstrated the feasibility of recording long latency CAEPs directly and solely through CI in adults with residual hearing, in response to acoustic stimulation of the non-implanted ear. The CI CAEPs closely resembled the CAEPs recorded simultaneously by an external EP system and via scalp electrodes. The ability to record directly from the implant, without the need of an external recording system, presents an innovative method with many clinical and research implications.

Postoperative Intracochlear Electrocochleography in Pediatric Cochlear Implant Recipients: Association to Audiometric Thresholds and Auditory Performance.

OBJECTIVES: The aim of this study was to compare intracochlear-recorded cochlear microphonics (CM) responses to behavioral audiometry thresholds in young children, with congenital hearing loss, 2 to 5 years after cochlear implantation early in life. In addition, differences in speech and auditory outcomes were assessed among children with and without residual hearing. DESIGN: The study was conducted at a tertiary, university-affiliated, pediatric medical center. CM responses by intracochlear electrocochleography technique were recorded from 102 implanted ears of 60 children and those responses correlated to behavioral audiometry thresholds at 0.125 to 2 kHz frequencies. All children had received Advanced Bionics cochlear implant with High Focus J1 or MidScala electrodes, along with extensive auditory rehabilitation before and after implantation, including the use of conventional hearing aids. Speech Spatial and Hearing Qualities, Category of Auditory Performance scale, and educational settings information were obtained for each participant. Those cochlear implantation (CI) outcomes were compared between children with or without residual CM responses. RESULTS: Two distinctive CM responses patterns were found among the implanted children. Of all ears diagnosed with cochlear hearing loss (n = 88), only in 29 ears, clear CM responses were obtained. In all other ears, no CM responses were obtained at the maximum output levels. The CM responses were highly correlated with coefficients ranging from 0.7 to 0.83 for the audiometric behavioral thresholds at 0.125 to 2 kHz frequency range. Of all ears diagnosed with auditory neuropathy syndrome disorder (n = 14), eight ears had residual hearing and recordable CM postimplantation. The other six ears showed no recordable CM responses at maximum output levels for all tested frequencies. Those showed supposedly better CM responses than the behavioral audiometry threshold, however with poor correlations with tested frequency thresholds. Children with residual hearing showed significantly better auditory outcomes with CI, compared with those without residual hearing. CONCLUSIONS: In children with congenital cochlear hearing loss, the objective CM intracochlear responses can reliably predict the residual audiometric threshold. However, in children with auditory neuropathy syndrome disorder, the CM thresholds did not match the behavioral audiometric responses. Postoperatively, children with recordable CM responses, showing preserved residual hearing, demonstrated better CI outcomes.