Distinguishing hair cell from neural potentials recorded at the round window.

Almost all patients who receive cochlear implants have some acoustic hearing prior to surgery. Electrocochleography (ECoG), or electrophysiological measures of cochlear response to sound, can identify remaining auditory nerve activity that is the basis for this residual hearing and can record potentials from hair cells that are no longer functionally connected to nerve fibers. The ECoG signal is therefore complex, being composed of both hair cell and neural signals. To identify signatures of different sources in the recorded potentials, we collected ECoG data across frequency and intensity from the round window of gerbils before and after treatment with kainic acid, a neurotoxin. Distortions in the recorded waveforms were produced by different sources over different ranges of frequency and intensity. In response to tones at low frequencies and low-to-moderate intensities, the major source of distortion was from neural phase-locking that was sensitive to kainic acid. At high intensities at all frequencies, the distortion was not sensitive to kainic acid and was consistent with asymmetric saturation of the hair cell transducer current. In addition to loss of phase-locking, changes in the envelope after kainic acid treatment indicate that sustained neural firing combines with receptor potentials from hair cells to produce the envelope of the response to tones. These results provide baseline data to interpret comparable recordings from human cochlear implant recipients.

An online database to improve clinical operations and scientific data collection in a pediatric hearing loss practice.

OBJECTIVE: To establish a pediatric hearing loss database that improves scientific data collection and clinical workflow in a large pediatric hearing loss and cochlear implant practice and incentivizes users to maintain careful scientific data collection and entry. PATIENTS: All children with hearing loss referred to the study institution. INTERVENTION: A multiuser multistation database was designed using a commercial database solution. Electronic data previously available were imported and verified. Various groups of professionals were educated on proper data entry methods. The database incorporated clinical information used in daily practice to ensure routine data entry and verification. MAIN OUTCOME MEASURES: Number of children entered into the database; user feedback on database feasibility; longitudinal speech perception performance in implanted children. RESULTS: Data import proved labor intensive but feasible. New data entry was facilitated by the instrument's usefulness in daily practice, which was readily accepted by the team involved in the management of pediatric hearing loss. Currently, the database includes more than 2,900 pediatric patients with hearing impairment, of which 1,034 have cochlear implants. Files contain audiometric, speech, anatomic, and surgical data. Speech perception performance increased with increasing age and duration of cochlear implant use for 478 children with speech perception data. CONCLUSION: The present database offers a powerful tool for scientific data collection and was easily integrated into the institution's busy clinical practice as a minimally time-consuming task. Database use facilitated querying for easy application to a number of clinical studies from this institution.

Round window electrocochleography just before cochlear implantation: relationship to word recognition outcomes in adults.

HYPOTHESES: Electrocochleography (ECoG) to acoustic stimuli can differentiate relative degrees of cochlear responsiveness across the population of cochlear implant recipients. The magnitude of the ongoing portion of the ECoG, which includes both hair cell and neural contributions, will correlate with speech outcomes as measured by results on CNC word score tests. BACKGROUND: Postoperative speech outcomes with cochlear implants vary from almost no benefit to near normal comprehension. A factor expected to have a high predictive value is the degree of neural survival. However, speech performance with the implant does not correlate with the number and distribution of surviving ganglion cells when measured postmortem. We will investigate whether ECoG can provide an estimate of cochlear function that helps predict postoperative speech outcomes. METHODS: An electrode was placed at the round window of the ear about to be implanted during implant surgery. Tone bursts were delivered through an insert earphone. Subjects included children (n = 52, 1-18 yr) and postlingually hearing impaired adults (n = 32). Word scores at 6 months were available from 21 adult subjects. RESULTS: Significant responses to sound were recorded from almost all subjects (80/84 or 95%). The ECoG magnitudes spanned more than 50 dB in both children and adults. The distributions of ECoG magnitudes and frequencies were similar between children and adults. The correlation between the ECoG magnitude and word score accounted for 47% of the variance. CONCLUSION: ECoGs with high signal-to-noise ratios can be recorded from almost all implant candidates, including both adult and pediatric populations. In postlingual adults, the ECoG magnitude is more predictive of implant outcomes than other nonsurgical variables such as duration of deafness or degree of residual hearing.