Electrically Evoked Auditory Brainstem Responses Threshold Research Articles

The effect of cochlear size on electrically evoked auditory brainstem responses in deaf children.

To investigate the relationship between auditory pathway function and cochlear size in deaf children with a radiologically normal inner ear or Mondini malformation. Thirty-five deaf children without inner ear malformations (IEMs) and forty cases with Mondini malformation were included in this study. The electrically evoked auditory brainstem responses (EABRs) evoked by electrical stimulation at the round window niche (RWN) and round window membrane (RWM) were recorded during cochlear implantation (CI) surgery. The anatomical parameters of the cochlea were assessed by high-resolution computed tomography and OTOPLAN 3-D construction software. Correlations between EABRs and cochlear sizes were analyzed. The EABR thresholds and/or latencies were negatively correlated with the basal cochlear diameter, cochlear width and/or cochlear duct length in both patients without IEMs and those with Mondini malformation. The physiological function of the peripheral auditory system depends on the anatomical structure of the cochlea to an extent. A larger cochlear size appears to be associated with better auditory conduction function. Our findings may be beneficial to selection of the proper electrode type and prediction of postoperative auditory rehabilitation. Level 4.

Electrically Evoked Auditory Brainstem Responses in Children Fitted with Hearing Aids Prior to Cochlear Implantation.

This study investigates the effect of hearing aid use on the peripheral auditory pathways in children with sensorineural hearing loss prior to cochlear implantation, as revealed by the electrically evoked auditory brainstem response (EABR). Forty children with hearing aids were recruited. Half of them had normal inner ear structures and the other half had inner ear malformations (IEMs). The EABR was evoked by electrically stimulating the round window niche (RWN) and round window membrane (RWM) during the cochlear implantation operation. The onset age of hearing aid use was significantly correlated with the peak latencies, but not amplitudes, of the wave III (eIII) and wave V (eV). Higher EABR thresholds were found for RWN stimulation than for RWM stimulation and in the children with IEMs than in those without IEMs. Our study provides neurophysiological evidence that earlier use of hearing aids may ameliorate physiological functions of the peripheral auditory pathway in children with and without IEMs. The EABR evoked by the electrical stimulation at RWM is more sensitive compared with that at RWN for evaluating functions of the auditory conduction pathway.

Evaluation of auditory pathway by EABR before cochlear implantation and the postoperative effect analysis.

To investigate the evaluation value of electrically evoked auditory brainstem response (EABR) monitoring before cochlear implantation in patients with cochlear nerve defects (CND). A total of 54 patients with cochlear nerve defects who underwent cochlear implantation in our hospital from 2011 to 2018 were selected as the CND group, and 20 patients with normal cochlear implantation were selected as the control group. The preoperative audiological characteristics, EABR characteristics and follow-up neural response telemetry results of the two groups were retrospectively analysed, and the preoperative EABR threshold and initiation C value were subjected to linear regression and correlation analysis. The EABR waveform of the CND group was significantly different from the control group in terms of average wave V threshold, average dynamic range and V-wave I/O curve slope (P < 0.05). Average C value and dynamic range had a statistically significant difference from the control group (P < 0.05). Statistically significant positive correlations were found between the EABR threshold and C value, wave V I/O slope and postoperative category of auditory perception (P < 0.05). The EABR test can be used to evaluate the auditory pathway function before cochlear implantation and its postoperative effect in patients with CND.

Electrically evoked auditory brainstem responses in deaf patients with Mondini malformation during cochlear implantation.

To investigate the auditory pathway functions in deaf patients with Mondini malformation using the electrically evoked auditory brainstem response (EABR) during cochlear implantation (CI). A total of 58 patients with severe to profound sensorineural hearing loss (SNHL) were included in this study. Of these patients, 27 cases had Mondini malformation and 31 control cases had no inner ear malformations (IEMs). Intraoperative EABRs evoked by electrical stimulation at the round window niche (RWN) and round window membrane (RWM) were recorded. Patients with Mondini malformation showed significantly lower EABR extraction rates than those with no IEMs did. However, for patients who showed EABRs, no significant difference in EABR thresholds, wave III (eIII) latencies, wave V (eV) latencies or eIII-eV latency intervals was found between two groups. The physiological functions of the peripheral auditory system in patients with Mondini malformation may divide into opposite extremes, as revealed by a robust EABR and the absence of the EABR, respectively. The auditory conduction function should be objectively and individually evaluated for patients with Mondini malformation by the EABR.

EABR THR Estimation Using High-Rate Multi-Pulse Stimulation in Cochlear Implant Users.

We estimated the electrically-evoked auditory brainstem response thresholds (eABR THRs) in response to multi-pulses with high burst rate of 10,000 pulses-per-second (pps). Growth functions of wave eV amplitudes, root mean square (RMS) values, peak of phase-locking value (PLV), and the lowest valid data point (LVDP) were calculated in 1-, 2-, 4-, 8-, and 16-pulses conditions. The growth functions were then fitted and extrapolated with linear and exponential functions to find eABR THRs. The estimated THRs were compared to psychophysical THRs determined for multi-pulse conditions as well as to the clinical THRs measured behaviorally at the rate of 1,000 pps. The growth functions of features showed shallower growth slopes when the number of pulses increased. eABR THRs estimated in 4-, 8-, and 16-pulses conditions were closer to the clinical THRs, when compared to 1- and 2-pulses conditions. However, the smallest difference between estimated eABR THRs and clinical THRs was not always achieved from the same number of pulses. The smallest absolute difference of 30.3 μA was found for the linear fittings on growth functions of eABR RMS values in 4-pulses condition. Pearson’s correlation coefficients (PCCs) between eABR THRs and psychophysical THRs were significant and relatively large in all but 16-pulses conditions. The PCCs between eABR THRs and clinical THRs, however, were smaller and in less cases significant. Results of this study showed that eABRs to multi-pulse stimulation could, to some extent, represent clinical stimulation paradigms, and thus in comparison to single pulses, could estimate clinical THRs with smaller errors.

The sensitivity of different methods for detecting abnormalities in auditory nerve function

BackgroundCochlear implants (CIs) have become important for the treatment of severe-to-profound sensorineural hearing loss (SNHL). Meanwhile, electrically evoked compound action potentials (ECAPs) and electrically evoked auditory brainstem responses (EABRs), which can be examined and evaluated with minimal patient cooperation, have become more reliable for tone measurement and speech recognition postoperatively. However, few studies have compared the electrophysiological characteristics of the auditory nerve using ECAPs and EABRs under different functional states of the auditory nerve (FSANs). We used guinea pig models in which six electrodes were implanted unilaterally with continuous electrical stimulation (ES) for 4 h. The amplitude growth functions (AGFs) of the alternating polarity ECAP (AP-ECAP) and forward-masking subtraction ECAP (FM-ECAP), as well as the EABR waves under “normal” and “abnormal” FSANs, were obtained.ResultsBoth the AP-ECAP and FM-ECAP thresholds were significantly higher than those measured by EABR under both “normal” FSAN and “abnormal” FSANs (p < 0.05). There was a significant difference in the slope values between electrodes 1 and 2 and electrodes 3 and 4 in terms of the AP-ECAP under the “abnormal” FSAN (p < 0.05). The threshold gaps between the AP-ECAP and FM-ECAP were significantly larger under the “abnormal” FSAN than under the “normal” FSAN (p < 0.05).ConclusionsBoth of the ECAP thresholds were higher than the EABR thresholds. The AP-ECAP was more sensitive than the FM-ECAP under the “abnormal” FSAN.

Examination and Comparison of Electrically Evoked Compound Action Potentials and Electrically Evoked Auditory Brainstem Response Results of Children with Cochlear Implantation without Inner Ear Anomaly.

To investigate the relationship between electrically evoked compound action potentials (ECAP) and electrically evoked auditory brainstem responses (EABR) in children with cochlear implants (CI) without inner ear anomalies. Sixteen children between the ages of two and six years who were CI users participated in the study. ECAP thresholds were recorded from one electrode in the basal, medial, and apical regions of the cochlear implant. EABRs were recorded from electrodes whose ECAP thresholds were determined. The latency-intensity functions, amplitude and morphological analyzes of the eIII and eV waves at 200 and 180 current unit (CU) excitation levels were performed. The data obtained were analyzed statistically. ECAP thresholds were found to be 171.5±11.38, 169.69±20.32 and 160.81±20.03 CU at the basal, medial and apical electrodes, respectively. EABR thresholds were also found to be 169.69±12.17, 165.62±16.41 and 160±15.49 CU in basal, medial and apical electrodes, respectively. There was a strong positive correlation between ECAP and EABR thresholds in apical, medial and basal electrodes (p<0.05). EABR threshold levels were not significantly different between basal, medial and apical region electrodes (p>0.05), and ECAP threshold values were significantly different between apical and basal region electrodes (p=0.002). When the significance values of EABR eV wave latencies were analyzed in terms of electrode region, the difference between basal and apical regions was found to be significant (p=0.03). Consistency was found between ECAP and EABR recordings. However, it was concluded that one could not be preferred over the other because the data quality of the two tests was different. In future studies, ECAP and EABR recordings may be recommended by selecting more electrodes for stimulation.

Chronic intracochlear electrical stimulation at high charge densities results in platinum dissolution but not neural loss or functional changes in vivo

Objective. Although there are useful guidelines defining the boundary between damaging and non-damaging electrical stimulation they were derived from acute studies using large surface area electrodes in direct contact with cortical neurons. These parameters are a small subset of the parameters used by neural stimulators. More recently, histological examination of cochleae from patients that were long-term cochlear implant users have shown evidence of particulate platinum (Pt). The pathophysiological effect of Pt within the cochlea is unknown. We examined the response of the cochlea to stimulus levels beyond those regarded as safe, and to evaluate the pathophysiological response of the cochlea following chronic stimulation at charge densities designed to induce Pt corrosion in vivo. Approach. 19 guinea pigs were systemically deafened and implanted with a cochlear electrode array containing eight Pt electrodes of 0.05, 0.075 or 0.2 mm2 area. Animals were electrically stimulated continuously for 28 d using charge balanced current pulses at charge densities of 400, 267 or 100 µC/cm2/phase. Electrically-evoked auditory brainstem responses (EABRs) were recorded to monitor neural function. On completion of stimulation electrodes were examined using scanning electron microscopy (SEM) and cochleae examined histology. Finally, analysis of Pt was measured using energy dispersive x-ray spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICP-MS). Main results. Compared with unstimulated control electrodes and electrodes stimulated at 100 µC/cm2/phase, stimulation at 267 or 400 µC/cm2/phase resulted in significant Pt corrosion. Cochleae stimulated at these high charge densities contained particulate Pt. The extent of the foreign body response depended on the level of stimulation; cochleae stimulated at 267 or 400 µC/cm2/phase exhibited an extensive tissue response that included a focal region of necrosis close to the electrode. Despite chronic stimulation at high charge densities there was no loss of auditory neurons (ANs) in stimulated cochleae compared with their contralateral controls. Indeed, we report a statistically significant increase in AN density proximal to electrodes stimulated at 267 or 400 µC/cm2/phase. Finally, there was no evidence of a reduction in AN function associated with chronic stimulation at 100, 267 or 400 µC/cm2/phase as evidenced by stable EABR thresholds over the stimulation program. Significance. Chronic electrical stimulation of Pt electrodes at 267 or 400 µC/cm2/phase evoked a vigorous tissue response and produced Pt corrosion products that were located close to the electrode. Despite these changes at the electrode/tissue interface there was no evidence of neural loss or a reduction in neural function.

Correlation between Preoperative Auditory Steady-State Response and Postoperative Electrically Evoked Auditory Brainstem Response and T Level in Cochlear Implantation for Child Patients with Inner-Ear Malformations

Objective: This study aims to investigate the correlation between thresholds of preoperative multiple auditory steady-state response (ASSR) and electrically evoked auditory brainstem response (EABR) and the behavioral threshold. Methods: A total of 72 patients were elected to receive a multichannel cochlear implant. According to the residual hearing determined in a preoperative test using high-, moderate-, and low-frequency ASSR, these patients were divided into the following 2 groups: residual hearing and hearing loss. The EABR and behavioral thresholds 1 year after implantation were assayed, and differences between these 2 parameters were compared. Results: Among the high-, moderate-, and low-frequency residual hearing groups, the EABR and behavioral thresholds of patients 1 year after implantation were significantly lower than those in the hearing loss group, and the differences were statistically significant (p < 0.01). Conclusion: Before the operation, ASSR results can be used to predict the efficacy of cochlear implantation in patients, and they serve as one of the reference conditions for choosing the ear for implantation. However, the threshold of ASSR is not equivalent to the actual auditory threshold of patients after implantation, and the deviation between these 2 thresholds is more significant at low frequencies.

[Evoked potentials in the rehabilitation of the patients after cochlear implantation].

The objective methods for the hearing examination of the patients after cochlear implantation provide an important tool for the speech processor fitting. The aim of the present study was to evaluate the possibilities and the informative value of the electrically evoked compound action potential (ECAP) and electrically evoked auditory brainstem response (EABR) combined recording technique. For this reason, the comparison of the ECAP and EABR thresholds with comfortable levels of stimulation, obtained on the basis of subjective response and psychophysical testing of the patients with good results after cochlear implantation was performed. 19 patients with the CI experience from 1 to 5 years were included in our study. The combined registration of ECAP and EABR can be used to evaluate the functional capacity of the central auditory pathways and for the fitting of the complicated patients, especially those in whom the registration proved impossible with the use of other objective techniques. The ECAP and EABR threshold values were well correlated with the individual stimulation map profiles in the patients with the CI experience of less than two years (p<0.05). The results obtained in the present study allow us to conclude that combined registration of ECAP and EABR could be used for the determination of stimulation comfort level parameters and individual stimulation map profiles, especially in combination with the minimum amount of psychoacoustic information received from the patient.

Characteristics of electrically evoked auditory brainstem responses in patients with cochlear nerve canal stenosis receiving cochlear implants

ObjectiveTo explore the characteristics of the electrically evoked auditory brainstem responses (EABR) in children with cochlear nerve canal stenosis (CNCs) following cochlear implantation (CI), and the EABR thresholds in children with stenotic versus normal cochlear nerve canals. MethodSixteen children with profound sensorineural hearing loss were included in this study: 8 with CNCs (CNCs group) and 8 with normal cochlear nerve canals (control group). All children underwent cochlear implantation with full insertion of all electrodes. EABR was performed 6 months postoperatively in both groups. ResultsThe EABR extraction rate was 100% in children with normal cochlear nerve canals and only 50% in children with CNCs. EABR thresholds were significantly higher in children with CNCs of electrodes No. 11and 22 than in children with normal cochlear nerve canals (P < 0.05 for both comparisons). There was no significant difference in EABR thresholds among electrode No. 1, 11 and 22 in CNCs group (P > 0.05 for all comparisons); while in the control group, the EABR threshold at electrode No 22 was lower than those at both electrodes No. 11 and 1 (P < 0.05 for both comparisons), and the EABR threshold at electrode No. 11 was also lower than that at electrode No. 1 (P < 0.05). ConclusionThe EABR thresholds in children with normal cochlear nerve canals vary according to the different locations of electrodes in the cochlea; while in children with CNCs, there was no significant difference among different electrode locations. The EABR thresholds in CNCs children were higher than those of children with normal cochlear nerve canals at electrode 11 and 22.

Postoperative objective detecting techniques for cochlear implant children with inner ear malformation

ObjectivesThis study aims to investigate the changing characteristics and rules of electrically-evoked auditory brainstem response (EABR), electrically-evoked stapedius reflex threshold (ESRT) and neural response telemetry (NRT) after cochlear implant in children with inner ear malformation, and guide postoperative equipment debug. MethodsA total of 88 children with either normal cochlea (control group) or inner ear malformation (test group) received Australian 24 multi-channel cochlear implants. The EABR, ESRT and NRT thresholds at different time points within one year postoperatively and behavioral responses (T-level and C-level) after one year were detected. Furthermore, the changing characteristics and rules of these thresholds were analyzed. ResultsThe EABR, ESRT and NRT thresholds were all significantly higher at all time points in the test group than in the control group, but the general changing trends were similar. Particularly, these thresholds worsened at low frequencies and improved at high frequencies. Furthermore, EABR, ESRT and NRT thresholds gradually increased during the one year postoperative period. In addition, an extremely significant correlation was found between EABR and T-level and between ESRT and C-level, but a less significant correlation was found between NRT threshold and T-level in both groups. ConclusionsThe postoperative changes in characteristics and rules of EABR, ESRT and NRT thresholds among cochlear implant children with inner ear malformation were all the same as those with normal cochlea. Thus, these thresholds can be used to guide the postoperative equipment debug for cochlear implants into patients with inner ear malformation.

Electric auditory brainstem response (E-ABR) in cochlear implant children: Effect of age at implantation and duration of implant use

AimThe objective of this study is to obtain stable and accurate electrically evoked auditory brainstem responses (EABR) in cochlear implant children and to evaluate the effect of age at implantation and duration of implant use on these responses. Method30 Children were implanted with Nucleus 24 cochlear implant. EABR recording were performed to all subjects using a stimulus with pulse width of 25μs/phase. The EABR signals were recorded from two electrodes (electrode 5 and 20) and at different intensities. The latency of the EABR waves III and V, and the EABR threshold were measured and analyzed. ResultsEABR waves could be recorded in 93.3% of the studied subjects. This study indicated better EABR responses at electrode 20 (apical electrode) relative to the basal site (electrode 5). EABR responses in children did not differ from adult responses. Moreover, the age of implantation and duration of implant use were correlated with EABR wave latencies and thresholds. ConclusionA well-established EABR was obtained in cochlear implant children with proper parameters. The characterizations of the EABR waves including wave latencies and threshold were extracted at different electrodes. The EABR test proves to be an effective method to evaluate the functions of the auditory pathway in children after cochlear implantation.

A clinical study of electrophysiological correlates of behavioural comfort levels in cochlear implantees

ObjectivesIndications for cochlear implantation have expanded today to include very young children and those with syndromes/multiple handicaps. Programming the implant based on behavioural responses may be tedious for audiologists in such cases, wherein matching an effective Measurable Auditory Percept (MAP) and appropriate MAP becomes the key issue in the habilitation program. In ‘Difficult to MAP’ scenarios, objective measures become paramount to predict optimal current levels to be set in the MAP. We aimed to (a) study the trends in multi-modal electrophysiological tests and behavioural responses sequentially over the first year of implant use; (b) generate normative data from the above; (c) correlate the multi-modal electrophysiological thresholds levels with behavioural comfort levels; and (d) create predictive formulae for deriving optimal comfort levels (if unknown), using linear and multiple regression analysis.MethodsThis prospective study included 10 profoundly hearing impaired children aged between 2 and 7 years with normal inner ear anatomy and no additional handicaps. They received the Advanced Bionics HiRes 90 K Implant with Harmony Speech processor and used HiRes-P with Fidelity 120 strategy. They underwent, impedance telemetry, neural response imaging, electrically evoked stapedial response telemetry (ESRT), and electrically evoked auditory brainstem response (EABR) tests at 1, 4, 8, and 12 months of implant use, in conjunction with behavioural mapping. Trends in electrophysiological and behavioural responses were analyzed using paired t-test. By Karl Pearson's correlation method, electrode-wise correlations were derived for neural response imaging (NRI) thresholds versus most comfortable level (M-levels) and offset based (apical, mid-array, and basal array) correlations for EABR and ESRT thresholds versus M-levels were calculated over time. These were used to derive predictive formulae by linear and multiple regression analysis. Such statistically predicted M-levels were compared with the behaviourally recorded M-levels among the cohort, using Cronbach's alpha reliability test method for confirming the efficacy of this method.ResultsNRI, ESRT, and EABR thresholds showed statistically significant positive correlations with behavioural M-levels, which improved with implant use over time. These correlations were used to derive predicted M-levels using regression analysis. On an average, predicted M-levels were found to be statistically reliable and they were a fair match to the actual behavioural M-levels. When applied in clinical practice, the predicted values were found to be useful for programming members of the study group. However, individuals showed considerable deviations in behavioural M-levels, above and below the electrophysiologically predicted values, due to various factors. While the current method appears helpful as a reference to predict initial maps in ‘difficult to Map’ subjects, it is recommended that behavioural measures are mandatory to further optimize the maps for these individuals.ConclusionThe study explores the trends, correlations and individual variabilities that occur between electrophysiological tests and behavioural responses, recorded over time among a cohort of cochlear implantees. The statistical method shown may be used as a guideline to predict optimal behavioural levels in difficult situations among future implantees, bearing in mind that optimal M-levels for individuals can vary from predicted values. In ‘Difficult to MAP’ scenarios, following a protocol of sequential behavioural programming, in conjunction with electrophysiological correlates will provide the best outcomes.

Relationship Between Electrically Evoked Auditory Brainstem Response and Auditory Performance After Cochlear Implant in Patients With Auditory Neuropathy Spectrum Disorder

To analyze the pattern of electrically evoked auditory brainstem response (EABR) in auditory neuropathy spectrum disorder (ANSD) patients and to compare their performances with controls. Retrospective analysis. Tertiary referral center. Eleven patients with ANSD and 9 control subjects with sensorineural hearing loss who did not have neural pathology. Diagnostic. Patients and control subjects each received a cochlear implant (CI) and underwent EABR. EABR threshold, wave V latency, and amplitude were measured as EABR parameters. The results of EABR were categorized as good response, variable response, or no response. Speech perception ability was assessed by the categories of auditory performance (CAP) score. All controls responded to EABR, whereas 6 of the 11 ANSD patients did not respond to EABR. The EABR threshold of the ANSD patients was measured almost within the value of disease controls. However, the Wave V latency displayed variable lengths, and the amplitude showed a wider distribution compared with the value of the disease control. The EABR response group among the ANSD patients showed relatively good performance after CI. In contrast, the nonresponse group demonstrated variable outcomes, although all of them still benefited from CI. The data suggested that all ANSD patients require CI and that EABR results can help establish realistic expectations about future performance. Even if electrical stimulation fails to generate sufficiently synchronized signal for eliciting EABR, CI provides at least partial, measurable auditory benefit in ANSD.

Spiral ganglion neuron survival and function in the deafened cochlea following chronic neurotrophic treatment

Cochlear implants electrically stimulate residual spiral ganglion neurons (SGNs) to provide auditory cues for the severe-profoundly deaf. However, SGNs gradually degenerate following cochlear hair cell loss, leaving fewer neurons available for stimulation. Providing an exogenous supply of neurotrophins (NTs) has been shown to prevent SGN degeneration, and when combined with chronic intracochlear electrical stimulation (ES) following a short period of deafness (5 days), may also promote the formation of new neurons. The present study assessed the histopathological response of guinea pig cochleae treated with NTs (brain-derived neurotrophic factor and neurotrophin-3) with and without ES over a four week period, initiated two weeks after deafening. Results were compared to both NT alone and artificial perilymph (AP) treated animals. AP/ES treated animals exhibited no evidence of SGN rescue compared with untreated deafened controls. In contrast, NT administration showed a significant SGN rescue effect in the lower and middle cochlear turns (two-way ANOVA, p < 0.05) compared with AP-treated control animals. ES in combination with NT did not enhance SGN survival compared with NT alone. SGN function was assessed by measuring electrically-evoked auditory brainstem response (EABR) thresholds. EABR thresholds following NT treatment were significantly lower than animals treated with AP (two-way ANOVA, p = 0.033). Finally, the potential for induced neurogenesis following the combined treatment was investigated using a marker of DNA synthesis. However, no evidence of neurogenesis was observed in the SGN population. The results indicate that chronic NT delivery to the cochlea may be beneficial to cochlear implant patients by increasing the number of viable SGNs and decreasing activation thresholds compared to chronic ES alone.

Identifying Cochlear Implant Channels With Poor Electrode-Neuron Interfaces: Electrically Evoked Auditory Brain Stem Responses Measured With the Partial Tripolar Configuration

The goal of this study was to compare cochlear implant behavioral measures and electrically evoked auditory brain stem responses (EABRs) obtained with a spatially focused electrode configuration. It has been shown previously that channels with high thresholds, when measured with the tripolar configuration, exhibit relatively broad psychophysical tuning curves. The elevated threshold and degraded spatial/spectral selectivity of such channels are consistent with a poor electrode-neuron interface, defined as suboptimal electrode placement or reduced nerve survival. However, the psychophysical methods required to obtain these data are time intensive and may not be practical during a clinical mapping session, especially for young children. Here, we have extended the previous investigation to determine whether a physiological approach could provide a similar assessment of channel functionality. We hypothesized that, in accordance with the perceptual measures, higher EABR thresholds would correlate with steeper EABR amplitude growth functions, reflecting a degraded electrode-neuron interface. Data were collected from six cochlear implant listeners implanted with the HiRes 90k cochlear implant (Advanced Bionics). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the partial tripolar configuration, for which a fraction of current (σ) from a center active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. EABRs were obtained in each subject for the two channels having the highest and lowest tripolar (σ = 1 or 0.9) behavioral threshold. Evoked potentials were measured with both the monopolar (σ = 0) and a more focused partial tripolar (σ ≥ 0.50) configuration. Consistent with previous studies, EABR thresholds were highly and positively correlated with behavioral thresholds obtained with both the monopolar and partial tripolar configurations. The Wave V amplitude growth functions with increasing stimulus level showed the predicted effect of shallower growth for the partial tripolar than for the monopolar configuration, but this was observed only for the low-threshold channels. In contrast, high-threshold channels showed the opposite effect; steeper growth functions were seen for the partial tripolar configuration. These results suggest that behavioral thresholds or EABRs measured with a restricted stimulus can be used to identify potentially impaired cochlear implant channels. Channels having high thresholds and steep growth functions would likely not activate the appropriate spatially restricted region of the cochlea, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.

F021 Myographic recording of the electrically elicited stapedius reflex

Increasing numbers of cochlear implant subjects have some level of residual hearing at the time of implantation. The present study examined whether (i) hair cells that have survived one pathological insult (aminoglycoside deafening), can survive and function following long-term cochlear implantation and electrical stimulation (ES); and (ii) chronic ES in these cochleae results in greater trophic support of spiral ganglion neurons (SGNs) compared with cochleae devoid of hair cells. Eight cats, with either partial (n = 4) or severe (n = 4) sensorineural hearing loss, were bilaterally implanted with scala tympani electrode arrays 2 months after deafening, and received unilateral ES using charge balanced biphasic current pulses for periods of up to 235 days. Frequency-specific compound action potentials and click-evoked auditory brainstem responses (ABRs) were recorded periodically to monitor the residual acoustic hearing. Electrically evoked ABRs (EABRs) were recorded to confirm the stimulus levels were 3–6 dB above the EABR threshold. On completion of the ES program the cochleae were examined histologically. Partially deafened animals showed no significant increase in acoustic thresholds over the implantation period. Moreover, chronic ES of an electrode array located in the base of the cochlea did not adversely affect hair cells in the middle or apical turns. There was evidence of a small but statistically significant rescue of SGNs in the middle and apical turns of stimulated cochleae in animals with partial hearing. Chronic ES did not, however, prevent a reduction in SGN density for the severely deaf cohort, although SGNs adjacent to the stimulating electrodes did exhibit a significant increase in soma area (p < 0.01). In sum, chronic ES in partial hearing animals does not adversely affect functioning residual hair cells apical to the electrode array. Moreover, while there is an increase in the soma area of SGNs close to the stimulating electrodes in severely deaf cochleae, this trophic effect does not result in increased SGN survival.

Brain Stem Responses Evoked by Stimulation of the Mature Cochlear Nucleus With an Auditory Brain Stem Implant

The Nucleus auditory brain stem implant (ABI) has been used in the hearing rehabilitation of totally deaf individuals for whom a cochlear implant is not an option such as in the case of neurofibromatosis type 2 (NF2). Intraoperative electrically evoked auditory brain stem responses (EABRs) are recorded to assist in the placement of the electrode array over the dorsal and ventral cochlear nuclei in the lateral recess of the IVth ventricle of the brain stem. This study had four objectives: (1) to characterize EABRs evoked by stimulation with an ABI in adolescents and adults with NF2, (2) to evaluate how the EABR morphology relates to auditory sensations elicited from stimulation by an ABI, (3) to establish whether there is evidence of morphology changes in the EABR with site of stimulation by the ABI, and (4) to investigate how the threshold of the EABR relates to behavioral threshold and comfortably loud sensations measured at initial device activation. Intraoperative EABRs were recorded from 34 subjects with ABIs: 19 male and 15 female, mean age 27 yrs (range 12 to 52 yrs). ABI stimulation was applied at seven different sites using either wide bipolar stimulation across the array or in subsections of the array from medial to lateral and inferior to superior. The EABRs were analyzed with respect to morphology, peak latency, and changes in these characteristics with the site of stimulation. In a subset of eight subjects, additional narrow bipolar sites were stimulated to compare the intraoperative EABR threshold levels with the behavioral threshold (T) and comfortably loud (C) levels of stimulation required at initial device activation. EABRs were elicited from 91% of subjects. Morphology varied from one to four vertex-positive peaks with mean latencies of 0.76, 1.53, 2.51, and 3.64 msecs, respectively. The presence of an EABR from stimulation by electrodes across the whole array had a high predictive value for the presence of auditory electrodes at initial device activation. When examining subsections of the array, the absence of an EABR was a poor predictor for the absence of auditory electrodes. The morphology of the EABRs varied with site of stimulation in 16 cases, but there was no consistent pattern of change with stimulation site. There was a trend for more auditory electrodes to be present in stimulation sites that evoked EABRs with a higher number of peaks in the waveform. The EABR threshold was closer to the behavioral C level than the T level, but there was no overall correlation between the intraoperative EABR threshold level and the behavioral T and C levels. The presence of an intraoperative EABR corresponded well to the presence of auditory electrodes. The absence of an EABR from stimulating subsections of the array was not; however, a good indicator for the absence of auditory electrodes and the EABR from such stimulation would not be of assistance in identifying the nonauditory sections of the array to exclude in behavioral fitting of the device. The morphology of the EABR did not relate to site of stimulation. More peaks in the EABR was associated with a greater number of electrodes with auditory sensations, suggesting that correct positioning of the ABI activated more auditory subsystems within the cochlear nucleus. The intraoperative EABR thresholds did not correlate with the behavioral T and C levels and could not be used to assist in device fitting.

Brain Stem Responses Evoked by Stimulation With an Auditory Brain Stem Implant in Children With Cochlear Nerve Aplasia or Hypoplasia

The inclusion criteria for an auditory brain stem implant (ABI) have been extended beyond the traditional, postlingually deafened adult with Neurofibromatosis type 2, to include children who are born deaf due to cochlear nerve aplasia or hypoplasia and for whom a cochlear implant is not an option. Fitting the ABI for these new candidates presents a challenge, and intraoperative electrically evoked auditory brain stem responses (EABRs) may assist in the surgical placement of the electrode array over the dorsal and ventral cochlear nucleus in the brain stem and in the postoperative programming of the device. This study had four objectives: (1) to characterize the EABR by stimulation of the cochlear nucleus in children, (2) to establish whether there are any changes between the EABR recorded intraoperatively and again just before initial behavioral testing with the device, (3) to establish whether there is evidence of morphology changes in the EABR depending on the site of stimulation with the ABI, and (4) to investigate how the EABR relates to behavioral measurements and the presence of auditory and nonauditory sensations perceived with the ABI at initial device activation. Intra- and postoperative EABRs were recorded from six congenitally deaf children with ABIs, four boys and two girls, mean age 4.2 yrs (range 3.2 to 5.0 yrs). The ABI was stimulated at nine different bipolar sites on the array, and the EABRs recorded were analyzed with respect to the morphology and peak latency with site of stimulation for each recording session. The relationship between the EABR waveforms and the presence or absence of auditory electrodes at initial device activation was investigated. The EABR threshold levels were compared with the behavioral threshold (T) and comfortably loud (C) levels of stimulation required at initial device activation. EABRs were elicited from all children on both test occasions. Responses contained a possible combination of one to three peaks from a total of four identifiable peaks with mean latencies of 1.04, 1.81, 2.61, and 3.58 msecs, respectively. The presence of an EABR was a good predictor of an auditory response; however, the absence of the EABR was poor at predicting a site with no auditory response. The morphology of EABRs often varied with site of stimulation and between EABR test occasions. Postoperatively, there was a trend for P1, P3, and P4 to be present at the lateral end of the array and P2 at the medial end of the array. Behavioral T and C levels showed a good correlation with postoperative EABR thresholds but a poor correlation with intraoperative EABR thresholds. The presence of an intraoperative EABR was a good indicator for the location of electrodes on the ABI array that provided auditory sensations. The morphology of the EABR was often variable within and between test sessions. The postoperative EABR thresholds did correlate with the behavioral T and C levels and could be used to assist with initial device fitting.