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

Abstract

Objective This study aimed to 1) characterize morphological characteristics of the electrically-evoked cortical auditory event-related potentials (eERP) and explore the potential association between onset eERP morphology and auditory vs non-auditory 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 five children (S1-S5) and two adults (S6-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-ms biphasic pulse train that was delivered to individual electrodes in a monopolar-coupled stimulation mode at stimulation levels ranging from sub-threshold 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 two to six 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 intra-subject variations in morphological characteristics of onset eERPs were observed. Onset eERPs with complex waveforms were recorded for electrodes that evoked non-auditory sensations, based on feedback from subjects, as well as for electrodes without any indications of non-auditory 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 intra-subject 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 th...

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

“…Another potential factor accounting for poor response repeatability observed in some participants is the change in stimulation level over time. eERPs in CI and ABI users showed decreased peak latency and increased peak amplitude as stimulation level increased (He et al, 2016; Visram et al, 2015). However, either reduced or absent responses were recorded at increased stimulation levels in several study participants (e.g.…”

“…The time interval between test sessions ranged from one to 35 months. In each session, prior to electrophysiological recordings, the maximum comfortable level (C level) was estimated for each ABI electrode using the procedure described in detail in our previous article (He et al, 2016). Briefly, an ascending and bracketing method was used.…”

“…Unfortunately, these three electrodes were only tested once for eERP recordings. Responses recorded for these electrodes have been reported in He et al (2016). These three electrodes were not repeatedly tested in any other sessions due to time constraints.…”

“…The intra-class correlation test was used to evaluate test-retest reliability of eERPs measured across test sessions. This statistical test takes both amplitude and latency differences into account and has been used successfully for the same purpose in several previously published studies (Friesen & Tremblay, 2006; He et al, 2013; He et al, 2016; Tremblay et al, 2003). Therefore, it is an appropriate statistical analysis test for this study.…”

“…The feasibility of measuring the eERP in children with ABIs has been established in our previous studies (He et al, 2015, 2016). Unlike the well-described P1-N2 complex for children with normal hearing and CIs, eERP recorded in children with ABIs show two types of waveform morphology.…”