Hypothesis Acoustically evoked neural and hair cell potentials can be measured from the round window (RW) intraoperatively in the general population of cochlear implant recipients. Background Cochlear implant performance varies greatly among patients. Improved methods to assess and monitor functional hair cell and neural substrate prior to and during implantation could potentially aid in enhanced non-traumatic intracochlear electrode placement and subsequent improved outcomes. Methods Subjects (1–80 years) undergoing cochlear implantation were included. A monopolar probe was placed at the RW after surgical access was obtained. The cochlear microphonic (CM), summating potential (SP), compound action potential (CAP), and auditory nerve neurophonic (ANN) were recorded in response to tone bursts at frequencies of 0.25 – 4 kHz at various levels. Results Measurable hair cell/neural potentials were detected to one or more frequencies in 23 of 25 subjects. The greatest proportion and magnitude of cochlear responses were to low frequencies (<1000 Hz). At these low frequencies the ANN, when present, contributed to the ongoing response at the stimulus frequency. In many subjects the ANN was small or absent while hair cell responses remained. Conclusions In cochlear implant recipients, acoustically evoked cochlear potentials are detectable even if hearing is extremely limited. Sensitive measures of cochlear and neural status can characterize the state of hair cell and neural function prior to implantation. Whether this information correlates with speech performance outcomes, or can help in tailoring electrode type, placement or audiometric fitting, can be determined in future studies.

In children with CND, the functional status of the CN varied along the length of the cochlea. Compared with children with normal-size CNs, children with CND showed reduced CN responsiveness to electrical stimuli. The prolonged CN absolute refractory period in children with CND might account for, at least partially, the observed benefit of using relatively slow pulse rate in these patients.

Objectives-The purpose of this study was to determine if changes in the position of the stimulating electrode in the cochlea could be used to elicit the electrically evoked auditory change complex (EACC) from Nucleus cochlear implant users.Design-Nine postlingually deafened adults participated in this study. Each study participant had been using his or her Nucleus CI24 cochlear implant for at least 3 months prior to testing. The speech processor was bypassed and the output of the implanted receiver/stimulator was controlled directly. The stimulus was a 600 ms burst of a biphasic pulse train (1000 pps). In control conditions, the stimulating electrode was held constant and stimulation continued throughout the 600 ms recording interval. In experimental conditions, the EACC was elicited by introducing a change in the stimulating electrode 300 ms after the onset of the pulse train. The EACC was recorded using surface electrodes. Three recordings of 100 sweeps each were obtained for each stimulus condition. Bandpass filtering (1 -100 Hz) was used to minimize contamination of the recordings by stimulus artifact. Averaged responses were then smoothed using a 40 ms wide boxcar filter and standard peak picking procedures were used to analyze these responses in the time domain.Results-In each case, a clear onset response (P1-N1-P2) was recorded. In the experimental conditions, a second evoked potential, the EACC, was also recorded following the change in stimulating electrode. This second response had general morphologic characteristics that were very similar to those of the onset response. Increasing the separation between the two stimulating electrodes in the experimental conditions resulted in a general trend toward increased EACC amplitudes.Conclusions-This report describes results of a set of experiments in which the speech processor of the cochlear implant was bypassed and the EACC was recorded in response to a change in stimulating electrode position. EACC amplitude was shown to increase as the separation between the two stimulating electrodes increased. While preliminary in nature, these results demonstrate the Correspondence: Carolyn J. Brown, PhD, 127B SHC, Dept. Speech Pathology and Audiology, University of Iowa, Iowa City, IA 52242, Phone: 319-335-8734, Fax: 319-335-8851, Email: carolyn-brown@uiowa.edu. Reprints: Use address listed above for correspondence Electrically evoked, auditory potentials were measured from Nucleus cochlear implant users. The speech processor was bypassed and the implanted electronics were controlled directly. A 600 ms train of biphasic current pulses was presented. In experimental conditions, the stimulus train included a change in the stimulating electrode position. The amplitude of the responses that were elicited by this change in electrode location tended to increase as the distance between the two stimulating electrodes increased. These results suggest that it may be feasible to use electrophysiologic techniques to assess sensitivity to change in various aspects of an ong...

The electrically evoked compound action potential (eCAP) represents the synchronous firing of a population of electrically stimulated auditory nerve fibers. It can be directly recorded on a surgically exposed nerve trunk in animals or from an intra-cochlear electrode of a cochlear implant. In the past two decades, the eCAP has been widely recorded in both animals and clinical patient populations using different testing paradigms. This paper provides an overview of recording methodologies and response characteristics of the eCAP, as well as its potential applications in research and clinical situations. Relevant studies are reviewed and implications for clinicians are discussed.