The electrically evoked cortical auditory event-related potential in children with auditory brainstem implants

Direct Elicitation of Cortical Auditory Evoked Potentials by Electrical Stimulation and Their Use to Verify the Most Comfortable Level of Stimulation in Cochlear Implant Users

INTRODUCTION

This study was designed to investigate the use of electrically evoked cortical auditory evoked potentials (eCAEPs) as a tool for cochlear implant (CI) verification, the relationships between the site and intensity of stimulation and the detection rates and morphologies of eCAEPs as well as investigate whether correlations exist between the morphologies of eCAEPs and speech perception in quiet and in noise, duration of hearing loss, age at implantation, whether the hearing loss bilateral or single-sided and the electrode current level required to elicit MCL stimulation.

METHODS

32 adult unilateral CI users with postlingual hearing loss were enrolled. The stimuli were 1 kHz biphasic alternating pulses and were presented at either the behaviorally measured MCL or 50% of this value (MCL0.5) via the CI fitting software. Pulses were directed to apical, medial, or basal electrodes. CAEPs were recorded from a scalp electrode placed at the vertex, low forehead, and contralateral mastoid and were evaluated by two electrophysiologists.

RESULTS

Overall, eCAEPs could be detected in 31/32 users when stimulating at MCL, and in 29/32 users when stimulating at MCL0.5. The detection rates were 31, 31, and 28/32 for apical, medial, and basal stimulation at MCL, and 29, 29, and 26/32 at MCL0.5. Significant differences in eCAEP amplitudes and latencies were observed across electrodes and stimulation levels. No significant correlations were found between eCAEP latencies and amplitudes and user age, duration of deafness prior to CI surgery, or with bilateral versus single-sided hearing loss, nor with the charge level required to elicit MCL, or with speech perception scores in quiet. Peak latencies correlated with speech perception scores in some configurations of speech-in-noise.

CONCLUSION

eCAEPs can readily be elicited in the majority of adult CI users and show normal waveform characteristics at stimulation levels corresponding to MCL, as well as at basal, medial, and apical electrode stimulation sites. Neither the latencies nor amplitudes of eCAEPs are confounded by variables of age, duration of deafness prior to CI surgery, or the laterality of hearing loss. eCAEPs are a useful, objective method evaluate sound perception in CI users.

Electrically Evoked Auditory Late Responses as a Novel Method for Cochlear Implant Programming

HYPOTHESIS

Electrically evoked auditory late responses (eALR) are useful as an objective cochlear implant (CI) fitting method.

BACKGROUND

Different objective and behavioral methods are used for CI fitting. However, there is no objective method that indicates that the electrical signal reaches the auditory cortex. eALR is an indicator that electrical signals reach the auditory cortex, so our aim was to investigate the use of eALR as an objective method for CI programming.

METHODS

Two different programs were created for 21 unilateral Med-El CI users. In the first program, the most comfortable level (MCL) was adjusted with the electrical stapes reflex threshold (eSRT), and the threshold levels (THR) were behaviorally adjusted according to the user's feedback. In the second program, the MCL level was adjusted to a level where all the components of the eALR were clearly seen, and the user did not feel uncomfortable; the THR levels were adjusted to the lowest level where the eALR P1 wave could be seen. The results of the MCL and THR levels of the two programs and the free field tests conducted with both programs were compared.

RESULTS

While MCL levels did not differ significantly between the two programs, a significant difference was observed between THR levels. In addition, no significant difference was found between hearing and speech tests with CI in the free field.

CONCLUSION

The results revealed no significant performance difference between the two programs and that eALR could be preferred as an objective method for MCL determination.

The Electrically Evoked Auditory Change Complex Evoked by Temporal Gaps Using Cochlear Implants or Auditory Brainstem Implants in Children With Cochlear Nerve Deficiency

OBJECTIVES

This study aimed to (1) establish the feasibility of measuring the electrically evoked auditory change complex (eACC) in response to temporal gaps in children with cochlear nerve deficiency (CND) who are using cochlear implants (CIs) and/or auditory brainstem implants (ABIs); and (2) explore the association between neural encoding of, and perceptual sensitivity to, temporal gaps in these patients.

DESIGN

Study participants included 5 children (S1 to S5) ranging in age from 3.8 to 8.2 years (mean: 6.3 years) at the time of testing. All subjects were unilaterally implanted with a Nucleus 24M ABI due to CND. For each subject, two or more stimulating electrodes of the ABI were tested. S2, S3, and S5 previously received a CI in the contralateral ear. For these 3 subjects, at least two stimulating electrodes of their CIs were also tested. For electrophysiological measures, the stimulus was an 800-msec biphasic pulse train delivered to individual electrodes at the maximum comfortable level (C level). The electrically evoked responses, including the onset response and the eACC, were measured for two stimulation conditions. In the standard condition, the 800-msec pulse train was delivered uninterrupted to individual stimulating electrodes. In the gapped condition, a temporal gap was inserted into the pulse train after 400 msec of stimulation. Gap durations tested in this study ranged from 2 up to 128 msec. The shortest gap that could reliably evoke the eACC was defined as the objective gap detection threshold (GDT). For behavioral GDT measures, the stimulus was a 500-msec biphasic pulse train presented at the C level. The behavioral GDT was measured for individual stimulating electrodes using a one-interval, two-alternative forced-choice procedure.

RESULTS

The eACCs to temporal gaps were recorded successfully in all subjects for at least one stimulating electrode using either the ABI or the CI. Objective GDTs showed intersubject variations, as well as variations across stimulating electrodes of the ABI or the CI within each subject. Behavioral GDTs were measured for one ABI electrode in S2 and for multiple ABI and CI electrodes in S5. All other subjects could not complete the task. S5 showed smaller behavioral GDTs for CI electrodes than those measured for ABI electrodes. One CI and two ABI electrodes in S5 showed comparable objective and behavioral GDTs. In contrast, one CI and two ABI electrodes in S5 and one ABI electrode in S2 showed measurable behavioral GDTs but no identifiable eACCs.

CONCLUSIONS

The eACCs to temporal gaps were recorded in children with CND using either ABIs or CIs. Both objective and behavioral GDTs showed inter- and intrasubject variations. Consistency between results of eACC recordings and psychophysical measures of GDT was observed for some but not all ABI or CI electrodes in these subjects.

Pediatric Auditory Brainstem Implantation: Surgical, Electrophysiologic, and Behavioral Outcomes

OBJECTIVES

The objectives of this study were to demonstrate the safety of auditory brainstem implant (ABI) surgery and document the subsequent development of auditory and spoken language skills in children without neurofibromatosis type II (NFII).

DESIGN

A prospective, single-subject observational study of ABI in children without NFII was undertaken at the University of North Carolina at Chapel Hill. Five children were enrolled under an investigational device exemption sponsored by the investigators. Over 3 years, patient demographics, medical/surgical findings, complications, device mapping, electrophysiologic measures, audiologic outcomes, and speech and language measures were collected.

RESULTS

Five children without NFII have received ABIs to date without permanent medical sequelae, although 2 children required treatment after surgery for temporary complications. All children wear their device daily, and the benefits of sound awareness have developed slowly. Intra-and postoperative electrophysiologic measures augmented surgical placement and device programming. The slow development of audition skills precipitated limited changes in speech production but had little impact on growth in spoken language.

CONCLUSIONS

ABI surgery is safe in young children without NFII. Benefits from device use develop slowly and include sound awareness and the use of pattern and timing aspects of sound. These skills may augment progress in speech production but progress in language development is dependent upon visual communication. Further monitoring of this cohort is needed to better delineate the benefits of this intervention in this patient population.

Electrically Evoked Auditory Event-Related Responses in Patients with Auditory Brainstem Implants: Morphological Characteristics, Test-Retest Reliability, Effects of Stimulation Level, and Association with Auditory Detection

OBJECTIVE

This study aimed to (1) characterize morphological characteristics of the electrically evoked cortical auditory event-related potentials (eERPs) and explore the potential association between onset eERP morphology and auditory versus nonauditory stimulation; (2) assess test-retest reliability of onset eERPs; (3) investigate effects of stimulation level on onset eERPs; and (4) explore the feasibility of using the onset eERP to estimate the lowest stimulation level that can be detected for individual stimulating electrodes in patients with auditory brainstem implants (ABIs).

DESIGN

Study participants included 5 children (S1 to S5) and 2 adults (S6 to S7) with unilateral Cochlear Nucleus 24M ABIs. Pediatric ABI recipients ranged in age from 2.6 to 10.2 years (mean: 5.2 years) at the time of testing. S6 and S7 were 21.2 and 24.6 years of age at the time of testing, respectively. S6 and S7 were diagnosed with neurofibromatosis II (NF2) and implanted with an ABI after a surgical removal of the tumors. All pediatric subjects received ABIs after being diagnosed with cochlear nerve deficiency. The lowest stimulation level that could be detected (behavioral T level) and the estimated maximum comfortable level (C level) was measured for individual electrodes using clinical procedures. For electrophysiological measures, the stimulus was a 100-msec biphasic pulse train that was delivered to individual electrodes in a monopolar-coupled stimulation mode at stimulation levels ranging from subthreshold to C levels. Electrophysiological recordings of the onset eERP were obtained in all subjects. For studies evaluating the test-retest reliability of the onset eERP, responses were measured using the same set of parameters in two test sessions. The time interval between test sessions ranged from 2 to 6 months. The lowest stimulation level that could evoke the onset eERP was defined as the objective T level.

RESULTS

Onset eERPs were recorded in all subjects tested in this study. Inter- and intrasubject variations in morphological characteristics of onset eERPs were observed. Onset eERPs with complex waveforms were recorded for electrodes that evoked nonauditory sensations, based on feedback from subjects, as well as for electrodes without any indications of nonauditory stimulations. Onset eERPs in patients with ABIs demonstrated good test-retest reliability. Increasing stimulation levels resulted in increased eERP amplitudes but showed inconsistent effects on response latencies in patients with ABIs. Objective and behavioral T levels were correlated.

CONCLUSIONS

eERPs could be recorded in both non-NF2 and NF2 patients with ABIs. eERPs in both ABI patient groups show inter- and intrasubject variations in morphological characteristics. However, onset eERPs measured within the same subject in this study tended to be stable across study sessions. The onset eERP can potentially be used to estimate behavioral T levels in patients with ABIs. Further studies with more adult ABI recipients are warranted to investigate whether the onset eERP can be used to identify electrodes with nonauditory stimulations.

Longitudinal Changes in Electrically Evoked Auditory Event-Related Potentials in Children With Auditory Brainstem Implants: Preliminary Results Recorded Over 3 Years

OBJECTIVES

This preliminary study aimed (1) to assess longitudinal changes in electrically evoked auditory event-related potentials (eERPs) in children with auditory brainstem implants (ABIs) and (2) to explore whether these changes could be accounted for by maturation in the central auditory system of these patients.

DESIGN

Study participants included 5 children (S1 to S5) with an ABI in the affected ear. The stimulus was a train of electrical pulses delivered to individual ABI electrodes via a research interface. For each subject, the eERP was repeatedly measured in multiple test sessions scheduled over up to 41 months after initial device activation. Longitudinal changes in eERPs recorded for each ABI electrode were evaluated using intraclass correlation tests for each subject.

RESULTS

eERPs recorded in S1 showed notable morphological changes for five ABI electrodes over 41 months. In parallel, signs or symptoms of nonauditory stimulation elicited by these electrodes were observed or reported at 41 months. eERPs could not be observed in S2 after 9 months of ABI use but were recorded at 12 months after initial stimulation. Repeatable eERPs were recorded in S3 in the first 9 months. However, these responses were either absent or showed remarkable morphological changes at 30 months. Longitudinal changes in eERP waveform morphology recorded in S4 and S5 were also observed.

CONCLUSIONS

eERP responses in children with ABIs could change over a long period of time. Maturation of the central auditory system could not fully account for these observed changes. Children with ABIs need to be closely monitored for potential changes in auditory perception and unfavorable nonauditory sensations. Neuroimaging correlates are needed to better understand the emergence of nonauditory stimulation over time in these children.

Auditory and audio-visual processing in patients with cochlear, auditory brainstem, and auditory midbrain implants: An EEG study

There is substantial variability in speech recognition ability across patients with cochlear implants (CIs), auditory brainstem implants (ABIs), and auditory midbrain implants (AMIs). To better understand how this variability is related to central processing differences, the current electroencephalography (EEG) study compared hearing abilities and auditory-cortex activation in patients with electrical stimulation at different sites of the auditory pathway. Three different groups of patients with auditory implants (Hannover Medical School; ABI: n = 6, CI: n = 6; AMI: n = 2) performed a speeded response task and a speech recognition test with auditory, visual, and audio-visual stimuli. Behavioral performance and cortical processing of auditory and audio-visual stimuli were compared between groups. ABI and AMI patients showed prolonged response times on auditory and audio-visual stimuli compared with NH listeners and CI patients. This was confirmed by prolonged N1 latencies and reduced N1 amplitudes in ABI and AMI patients. However, patients with central auditory implants showed a remarkable gain in performance when visual and auditory input was combined, in both speech and non-speech conditions, which was reflected by a strong visual modulation of auditory-cortex activation in these individuals. In sum, the results suggest that the behavioral improvement for audio-visual conditions in central auditory implant patients is based on enhanced audio-visual interactions in the auditory cortex. Their findings may provide important implications for the optimization of electrical stimulation and rehabilitation strategies in patients with central auditory prostheses. Hum Brain Mapp 38:2206-2225, 2017. © 2017 Wiley Periodicals, Inc.