Neurophysiology of Cochlear Implant Users I: Effects of Stimulus Current Level and Electrode Site on the Electrical ABR, MLR, and N1-P2 Response

Abstract

Objective: As the need for objective measures with cochlear implant users increases, it is critical to understand how electrical potentials behave when stimulus parameters are systematically varied. The purpose of this study was to record and evaluate the effects of implanted electrode site and stimulus current level on latency, amplitude, and threshold measures of electrically evoked auditory potentials, representing brainstem and cortical levels of the auditory system. Design:The electrical auditory brainstem response (EABR), electrical auditory middle latency response (EAMLR), and the electrical late auditory response (ELAR) were recorded from the same experimental subjects, 11 adult Clarion cochlear implant users. The Waves II, III, and V of the EABR, the Na-Pa complex of the EAMLR and the N1-P2 complex of the ELAR were investigated relative to electrode site (along the intra-cochlear electrode array) and stimulus current level. Evoked potential measures were examined for statistical significance using analysis of variance (ANOVA) for repeated measures.Results: For the EABR, Wave V latency was significantly longer for the basal electrode (7) compared with the mid (4) and apical (1) electrodes. For the EAMLR and ELAR, there were no significant differences in latency by electrode site. For all subjects and each of the evoked potentials, the apical electrodes tended to have the largest amplitude and the basal electrodes the smallest amplitude, although amplitude differences did not reach statistical significance. In general, decreases in stimulus current level resulted in statistically significant decreases in the amplitude of Wave V, Na-Pa and N1-P2. The evoked potential thresholds for Wave V, Na-Pa, and N1-P2 were significantly higher for the basal Electrode 7 than for Electrodes 4 and 1. Conclusions: Electrophysiologic responses of Waves

An Evoked Potential Study of the Developmental Time Course of the Auditory Nerve and Brainstem in Children Using Cochlear Implants

“…Interestingly, eIII-eV latencies were fairly consistent between these studies (approximately 1.85 ms) despite differences in device (single vs. multi-electrode implants), differences in stimulus presentation rates (10-60 Hz), and differences in intensity (near electrophysiologic threshold -uncomfortable loudness limits). More recent eIII-eV data from adults [Firszt et al, 2002] indicated a 1.62-ms latency which was more like the adult data reported in the present study (1.69 8 0.09 ms). It is possible that the adult data is subject to large sample variations because adults tend to have widely varied aetiologies and durations of deafness prior to implantation.…”

“…It is possible that the adult data is subject to large sample variations because adults tend to have widely varied aetiologies and durations of deafness prior to implantation. Moreover, cochlear implant technologies change with time; perhaps the fact that the study by Firszt et al [2002] was conducted with implant users using devices of similar generations to those used in the present study helps to explain why their results are more similar to those presented here than were results of the older studies.…”

The Effect of Intensity on the Speech Evoked Auditory Late Latency Response in Normal Hearing Individuals

“…In a previous study [17] , intensity function in hearing impaired elderly in aided conditionswas investigated by varying the intensity of the pure tones through a hearing aid, and it was reported that a larger amplitude at P2 only in the aided condition. Some authors have studied the effect of the stimulus level by increasing the current levels in cochlear implant recipients, such as Firszt, Chambers, Kraus, Reeder and Kim, Brown, Abbas, Etler, O'Brien [21,22] where they presented biphasic current pulses of varying magnitude as stimuli and found a decreased latency and increased amplitude of the N1 and P2 components as the stimulus level increased. Only very few studies have reported speech stimulus level effects in normal-hearing individuals [12] .…”

Evidence of a Tonotopic Organization of the Auditory Cortex in Cochlear Implant Users

“…This latency was measured for each subset of recording electrodes. Such a wide time window was explored because of the high variability of N1 latency in cochlear implantees, something that appears to depend on the duration of deafness (Guiraud et al, 2007), the duration of implant use (Gordon et al, 2004), and the intensity of stimulation (Firszt et al, 2002). The N1 amplitude for each subset of electrodes was then measured as the average amplitude over a 30 ms time window around the corresponding peak latency.…”