Bilateral Cochlear Implant Processing of Coding Strategies With CCi-MOBILE, an Open-Source Research Platform

While speech understanding for cochlear implant (CI) users in quiet is relatively effective, listeners experience difficulty in identification of speaker and sound location. To assist for better residual hearing abilities and speech intelligibility support, bilateral and bimodal forms of assisted hearing is becoming popular among CI users. Effective bilateral processing calls for testing precise algorithm synchronization and fitting between both left and right ear channels in order to capture interaural time and level difference cues (ITD and ILDs). This work demonstrates bilateral implant algorithm processing using a custom-made CI research platform - CCi-MOBILE, which is capable of capturing precise source localization information and supports researchers in testing bilateral CI processing in real-time naturalistic environments. Simulation-based, objective, and subjective testing has been performed to validate the accuracy of the platform. The subjective test results produced an RMS error of ±8.66° for source localization, which is comparable to the performance of commercial CI processors.

Modulation Depth Discrimination by Cochlear Implant Users

Cochlear implants (CIs) convey the amplitude envelope of speech by modulating high-rate pulse trains. However, not all of the envelope may be necessary to perceive amplitude modulations (AMs); the effective envelope depth may be limited by forward and backward masking from the envelope peaks. Three experiments used modulated pulse trains to measure which portions of the envelope can be effectively processed by CI users as a function of AM frequency. Experiment 1 used a three-interval forced-choice task to test the ability of CI users to discriminate less-modulated pulse trains from a fully modulated standard, without controlling for loudness. The stimuli in experiment 2 were identical, but a two-interval task was used in which participants were required to choose the less-modulated interval, ignoring loudness. Catch trials, in which judgements based on level or modulation depth would give opposing answers, were included. Experiment 3 employed novel stimuli whose modulation envelope could be modified below a variable point in the dynamic range, without changing the loudness of the stimulus. Overall, results showed that substantial portions of the envelope are not accurately encoded by CI users. In experiment 1, where loudness cues were available, participants on average were insensitive to changes in the bottom 30% of their dynamic range. In experiment 2, where loudness was controlled, participants appeared insensitive to changes in the bottom 50% of the dynamic range. In experiment 3, participants were insensitive to changes in the bottom 80% of the dynamic range. We discuss potential reasons for this insensitivity and implications for CI speech-processing strategies.

Comparison of Clinician Versus Parental Perspectives of Outcomes in Cochlear Implantees: A South Indian Experience

Outcomes of cochlear implantation (CI) are generically assessed using standard validated measures like CAP, SIR, MAIS and MUSS scales. Although this reflects the improvement in auditory verbal skills among the implantees with habilitation over one year, the overall perception of their skill development may vary between the parents of these children and the clinicians who provide the habilitation. This study aimed to compare the CAP and SIR scores sequentially over habilitation and further analyzes the correlation between clinician assessment (with CAP/SIR scores) and parental perspective (with MAIS/MUSS scores), at the end of one year of habilitation. 388 children aged 1-6 years who underwent unilateral CI were included in the study. Their baseline CAP and SIR scores were recorded post implantation. All children received 1 year of intensive auditory verbal therapy and their 12 month CAP, SIR, MAIS and MUSS scores were then recorded. The baseline CAP/SIR scores were compared with 12 month CAP/SIR scores and then their 12 month CAP/SIR scores were correlated with 12 month MAIS/MUSS scores respectively. There was significant difference between baseline and the 12 month CAP/SIR scores (p < 0.001). There was strong positive correlation between CAP and SIR scores after 12 months of habilitation (r = 0.7), while there was moderate positive correlation between CAP and MAIS scores (r = 0.59) and between SIR and MUSS scores (r = 0.49) respectively. Though the parents note significant improvement in child's communication abilities, the parental perspective of final outcomes does not always match with the clinician's assessments at the end of habilitation, as highlighted by the moderate correlations. A more precise method of holistic assessment is lacking currently and stands warranted.

Optimizing stimulation parameters to record electrically evoked cortical auditory potentials in cochlear implant users

Objectives: To measure the effect of burst duration, stimulated electrode position, and stimulation level on the P1-N1-P2 electrically evoked cortical auditory potentials (eCAEPs) elicited via the direct stimulation of selected electrode contacts on a cochlear implant (CI) electrode array.Methods: Prospective observational study of 20 adult cochlear implant users with a MED-EL CI system. eCAEPs were recorded simultaneously with the Eclipse (Interacoustics) and the Neuropack S1 MEB-9400 (Nihon Kohden) recording systems. Tone bursts with durations of 50, 100, and 150 ms were used for stimulation at the maximum comfortable loudness level (MCL) and MCL minus 50% dynamic range (DR) at selected apical, medial, and basal intracochlear electrodes.Results: Individual P1-N1 and N1-P2 amplitudes were significantly higher at the MCL level of stimulation than at the MCL minus 50% DR. Burst length and stimulated electrode position did not affect the eCAEP responses. Residual noise was lower in the Neuropack S1 MEB-9400 system.Conclusions: This study shows the feasibility of eCAEP recording using the MAESTRO software. The eCAEP morphology was independent of the burst duration and the stimulated electrode position. This allows a large flexibility in using direct cochlear stimulation to elicit eCAEPs.

Opposite Roles of NT-3 and BDNF in Synaptic Remodeling of the Inner Ear Induced by Electrical Stimulation

With the development of neural prostheses, neural plasticity including synaptic remodeling under electrical stimulation is drawing more and more attention. Indeed, intracochlear electrical stimulation used to restore hearing in deaf can induce the loss of residual hearing and synapses of the inner hair cells (IHCs). However, the mechanism under this process is largely unknown. Considering that the guinea pig is always a suitable and convenient choice for the animal model of cochlea implant (CI), in the present study, normal-hearing guinea pigs were implanted with CIs. Four-hour electrical stimulation with the intensity of 6 dB above electrically evoked compound action potential (ECAP) threshold (which can decrease the quantity of IHC synapses and the excitability of the auditory nerve) resulted in the upregulation of Bdnf (p < 0.0001) and downregulation of Nt-3 (p < 0.05). Intracochlear perfusion of exogenous NT-3 or TrkC/Fc (which blocks NT-3) can, respectively, resist or aggravate the synaptic loss induced by electrical stimulation. In contrast, local delivery of exogenous BDNF or TrkB/Fc (which blocks BDNF) to the cochlea, respectively, exacerbated or protected against the synaptic loss caused by electrical stimulation. Notably, the synaptic changes were only observed in the basal and middle halves of the cochlea. All the findings above suggested that NT-3 and BDNF may play opposite roles in the remodeling of IHC synapses induced by intracochlear electrical stimulation, i.e. NT-3 and BDNF promoted the regeneration and degeneration of IHC synapses, respectively.

Neurotrophin gene therapy to promote survival of spiral ganglion neurons after deafness

Hearing impairment is a major health and economic concern worldwide. Currently, the cochlear implant (CI) is the standard of care for remediation of severe to profound hearing loss, and in general, contemporary CIs are highly successful. But there is great variability in outcomes among individuals, especially in children, with many CI users deriving much less or even marginal benefit. Much of this variability is related to differences in auditory nerve survival, and there has been substantial interest in recent years in exploring potential therapies to improve survival of the cochlear spiral ganglion neurons (SGN) after deafness. Preclinical studies using osmotic pumps and other approaches in deafened animal models to deliver neurotrophic factors (NTs) directly to the cochlea have shown promising results, especially with Brain-Derived Neurotrophic Factor (BDNF). More recent studies have focused on the use of NT gene therapy to force expression of NTs by target cells within the cochlea. This could provide the means for a one-time treatment to promote long-term NT expression and improve neural survival after deafness. This review summarizes the evidence for the efficacy of exogenous NTs in preventing SGN degeneration after hearing loss and reviews the animal research to date suggesting that NT gene therapy can elicit long-term NT expression in the cochlea, resulting in significantly improved SGN and radial nerve fiber survival after deafness. In addition, we discuss NT gene therapy in other non-auditory applications and consider some of the remaining issues with regard to selecting optimal vectors, timing of treatment, and place/method of delivery, etc. that must be resolved prior to considering clinical application.

Cochlear Implantation in Children with Usher's Syndrome: A South Asian Experience

Usher's syndrome is an autosomal recessive disorder characterized by dual sensory impairment involving both the ears and eyes. Cochlear implantation paves a way to restore hearing loss in such individuals but poor vision among these patients poses additional challenges for the habilitationists. This study aimed to compare the habilitation outcomes and hearing-related quality of life scores of cochlear implantees having Usher syndrome with age-matched cochlear implantees with no such syndromic association. 27 patients aged 1-6 years with Usher syndrome underwent cochlear Implantation over a period of 10 years from 2006 to 2016 and were included in this study along with an age-matched cohort of 30 implantees with no additional disabilities. Category of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) scores were compared at 3, 6, 9 and 12 months respectively. Glasgow Benefit Inventory and Health Utility Index (HUI 3.0) questionnaires were used to assess the hearing-related quality of life in both groups at 1 year post implantation. There was significant difference in CAP and SIR scores between children with Usher's syndrome and the control group (p < 0.05). The overall scores in terms of quality of life as well were statistically different (p < 0.05). Though there was improvement in speech and language acquisition after cochlear Implantation this was found to be of lesser extent than the normative cohort. These children with additional visual disabilities required intensive, individualized therapy catering to their complex needs. Their family's perception of expected benefit from cochlear Implantation was guarded and needed to be appraised in detail prior to surgery. This experience helped prepare an institutional protocol for counseling such implantees in future.

Radiological Anatomy of Inner Ear Malformation in Hearing Impaired Children and it's Correlation with Hearing Loss: A Hospital Based Observational Study

To see the radiological anatomy of inner ear malformations in hearing impaired children. This study was a prospective observational study done at a tertiary care teaching hospital in north India. The included were children of 1-7 years with first time detected severe to profound SNHL. The evaluation of hearing was done by brainstem evoked response audiometry. Those with history of chronic suppurative otitis media and conductive hearing loss were excluded. The all included were undergone high resolution computed tomography of the tympano-mastoid region. A written informed consent was taken. The institutional ethics committee approved the study protocol. We screened 130 children of 1-7 years of age with complaints of severe to profound hearing impairment (SNHL) by BERA. We excluded 38 and 14 children who had conductive hearing loss with or without CSOM and did not give consent, respectively. Among recruited 78 children, 47 (60.3%) had severe (71-90 dB) and 31 (39.7%) had profound (> 90 dB) SNHL. The majority of children (60/78, 76.9%) had a bilateral hearing impairment, only 18 (23.1%) had unilateral hearing impairment. The mean ± SD of age was 3.9 ± 1.3 years (95% CI = 3.6-4.2). The incidence of severe to profound SNHL was higher, though not statistically significant among the girls. Only 7.7% children with severe to profound SNHL were detected within first 2 years of life. Most of the children (92.3%) with severe to profound SNHL were detected after 2 years of age. Among 78 with severe to profound SNHL, 16 (20.5%) children had structural anomalies in their internal ears. Only 2 (6.9%) ears had single anomaly, others (27, 93.1%) had multiple anomalies. A maximum number of anomalies found in one ear were 5. The most common anomalies were found in the vestibule. The total number of anomalies were 115. Five children (6.4%) with severe to profound SNHL had craniofacial dysmorphism. Approximately 20% of children with severe to profound SNHL have congenital anomalies in their internal ears. It is crucial to know these anomalies before planning of CI. HRCT of tympano-mastoid is the first modality to know these anomalies. MRI should also be included to know the details of vestibulocochlear nerve. Since, the neurocognitive outcome would be the best if CI will be done as early as possible preferably around 1 year of age. Therefore, children must be screened at the appropriate age, firstly by OAE followed by BERA.

Cochlear implant outcomes in patients with superior canal dehiscence

OBJECTIVE

To determine whether adult cochlear implant (CI) users with superior canal dehiscence syndrome (SCDS) or asymptomatic superior semicircular canal dehiscence (SCD) have different surgical, vestibular, and audiologic outcomes when compared to CI users with normal temporal bone anatomy.

METHODS

A retrospective single institution review of CI users with either superior semicircular canal dehiscence syndrome or asymptomatic superior semicircular canal dehiscence identified eight post-lingually deafened adults with unilateral or bilateral cochlear implantation between 2006 and 2010. Preoperative and postoperative speech perception scores as well as medical and epidemiological data were recorded and analyzed.

RESULTS

One patient with superior canal dehiscence syndrome and seven patients with asymptomatic superior semicircular canal dehiscence were identified, representing 7% or 8/113 of CI patients that fulfilled selection criteria. Average dehiscence length was 3.3 mm ± 0.79 SEM. Three patients received bilateral implants and five patients received a unilateral implant. Among asymptomatic superior semicircular canal dehiscence patients, subjective rates of post-operative dizziness were similar to those seen in patients with normal temporal bone anatomy (12.5 % vs. 15.9%, respectively). Speech perception abilities after surgery were poorer in SCD patients compared to the non-SCD cohort (Consonant Nucleus Consonant 33.7 ± 7.78 SEM vs. 56.7 ± 2.15 SEM P = 0.011), although both groups improved substantially relative to pre-operative performance. We also completed detailed analyses of auditory and vestibular outcomes in one patient with SCDS who underwent CI surgery in the symptomatic ear, which demonstrated preservation of vestibular function post-operatively, improved quality-of-life measures, and reduced dizziness symptomatology.

CONCLUSIONS

Our data suggest that patients with asymptomatic superior canal dehiscence at the time of CI surgery have similar albeit decreased speech perception scores compared to non-SCD adult CI users. Subjective rate of dizziness or vertigo following CI surgery was similar in both asymptomatic SCD and non-SCD cohorts, with detailed analyses of a single symptomatic SCD patient revealing improved vestibular function and reduced SCD symptoms following CI.