Auditory implant research at the House Ear Institute 1989-2013

Combining Place and Rate of Stimulation Improves Frequency Discrimination in Cochlear Implant Users

In the auditory system, frequency is represented as tonotopic and temporal response properties of the auditory nerve. While these response properties are inextricably linked in normal hearing, cochlear implants can separately excite tonotopic location and temporal synchrony using different electrodes and stimulation rates, respectively. This separation allows for the investigation of the contributions of tonotopic and temporal cues for frequency discrimination. The present study examines frequency discrimination in adult cochlear implant users as conveyed by electrode position and stimulation rate, separately and combined. The working hypothesis is that frequency discrimination is better provided by place and rate cues combined compared to either cue alone. This hypothesis was tested in two experiments. In the first experiment, frequency discrimination needed for melodic contour identification was measured for frequencies near 100, 200, and 400 Hz using frequency allocation modeled after clinical processors. In the second experiment, frequency discrimination for pitch ranking was measured for frequencies between 100 and 1600 Hz using an experimental frequency allocation designed to provide better access to place cues. The results of both experiments indicate that frequency discrimination is better with place and rate cues combined than with either cue alone. These results clarify how signal processing for cochlear implants could better encode frequency into place and rate of electrical stimulation. Further, the results provide insight into the contributions of place and rate cues for pitch.

Advances in auditory implants

Auditory implants are classified into bone conduction (BAHA and Bonebridge; BB) and active middle ear implants (Vibrant Soundbridge; VSB) that stimulate cochlear hair cells, and cochlear implants (CIs) that stimulate neural structures. CIs should be performed as early as possible, and bilateral CIs have become popular because sound localization and speech recognition can be improved. CI is also considered a desirable treatment option for patients with single-sided deafness. VSB provides a safe and effective option for patients with conductive or mixed hearing loss and moderate to severe sensorineural hearing loss (SNHL); however, it use in patients with conductive or mixed hearing loss have only been approved in Japan. BAHA and BB implants have been approved by national insurance in Japan as bone conduction implants for patients with conductive or mixed hearing loss. Two fully implantable devices (Cochlear Carina and Envoy Esteem) are provided for patients with SNHL.

Written language skills in children with auditory brainstem implants

PURPOSE

This study aimed to assess the written language skills of children with auditory brainstem implants (ABI).

METHODS

In this study, 15 children (from second to eighth grades) with ABI were evaluated for their written language abilities using a written expression skill assessment form. Five different features of written expression points were scored and analyzed, yielding a composite score for written expression skills.

RESULTS

This study showed that all children with ABI needed more verbal cues than spontaneously written samples. Moreover, these children used short and simple sentences with limited vocabulary and repeated words and sentences. Furthermore, these children were deficient in writing an introduction, the body, and the conclusion paragraphs and could not write events in a logical sequence.

CONCLUSIONS

The written language skills of children with ABI depend on age at implantation, duration of implant use, and additional handicaps. Written expression skills in children with ABI are highly complex skills. The findings highlight the importance of ABI during the critical language development period and the enhancement of training programs for written language skills in children who underwent ABI.

Perceptual learning of pitch provided by cochlear implant stimulation rate

Cochlear implant users hear pitch evoked by stimulation rate, but discrimination diminishes for rates above 300 Hz. This upper limit on rate pitch is surprising given the remarkable and specialized ability of the auditory nerve to respond synchronously to stimulation rates at least as high as 3 kHz and arguably as high as 10 kHz. Sensitivity to stimulation rate as a pitch cue varies widely across cochlear implant users and can be improved with training. The present study examines individual differences and perceptual learning of stimulation rate as a cue for pitch ranking. Adult cochlear implant users participated in electrode psychophysics that involved testing once per week for three weeks. Stimulation pulse rate discrimination was measured in bipolar and monopolar configurations for apical and basal electrodes. Base stimulation rates between 100 and 800 Hz were examined. Individual differences were quantified using psychophysically derived metrics of spatial tuning and temporal integration. This study examined distribution of measures across subjects, predictive power of psychophysically derived metrics of spatial tuning and temporal integration, and the effect of training on rate discrimination thresholds. Psychophysical metrics of spatial tuning and temporal integration were not predictive of stimulation rate discrimination, but discrimination thresholds improved at lower frequencies with training. Since most clinical devices do not use variable stimulation rates, it is unknown to what extent recipients may learn to use stimulation rate cues if provided in a clear and consistent manner.

The Importance of Early Genetic Diagnostics of Hearing Loss in Children

Hearing loss is one of the most common sensory deficits. It carries severe medical and social consequences, and therefore, universal newborn hearing screening was introduced at the beginning of this century. Affected patients can have hearing loss as a solitary deficit (non-syndromic hearing loss) or have other organs affected as well (syndromic hearing loss). In around 60% of cases, congenital hearing loss has a genetic etiology, where disease-causing variants can change any component of the hearing pathway. Genetic testing is usually performed by sequencing. Sanger sequencing enables analysis of the limited number of genes strictly preselected according to the clinical presentation and the prevalence among the hearing loss patients. In contrast, next-generation sequencing allows broad analysis of the numerous genes related to hearing loss, exome, or the whole genome. Identification of the genetic etiology is possible, and it makes the foundation for the genetic counselling in the family. Furthermore, it enables the identification of the comorbidities that may need a referral for specialty care, allows early treatment, helps with identification of candidates for cochlear implant, appropriate aversive/protective management, and is the foundation for the development of novel therapeutic options.

Pediatric Auditory Brainstem Implant Users Compared With Cochlear Implant Users With Additional Disabilities

OBJECTIVES

To evaluate long-term language development in children with prelingual deafness who received auditory brainstem implants (ABIs) compared with children who received cochlear implants (CIs) at the same hospital. Additional non-auditory disabilities were taken into account.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary referral center.

PATIENTS

Ten children with bilateral malformations of the cochlea and/or cochlear nerve who received ABIs, including seven with additional disabilities, and 147 children with CIs as a reference group, including 22 children with additional disabilities.

INTERVENTION

ABIs were implanted at 1.3 to 6.2 years of age. Follow-up ranged from 1.1 to 7.7 years.

MAIN OUTCOME MEASURES

Receptive and expressive language abilities were assessed using the Infant Toddler Meaningful Auditory Integration Scale (IT-MAIS), the Categories of Auditory Performance (CAP), the Meaningful Use of Speech Scale (MUSS), and the Speech Intelligibility Rate (SIR).

RESULTS

Of the 10 children with ABIs, seven had long-term follow-up data. Within 1 year, six of the seven children with ABIs could identify sounds, respond to speech, and use their voice to attract attention. Language skills developed at a slower rate than in children with CIs and reached the same competence level when additional disabilities were absent. These language skills matched, on average, those of children with CIs with additional disabilities.

CONCLUSION

For deaf children with bilateral inner ear malformations, ABIs provide satisfactory auditory input. Children with ABIs are able to develop receptive and expressive language skills comparable to those of children with CIs with additional disabilities. Using this knowledge, preoperative parent counselling can be refined.

Effect of anesthesia on evoked auditory responses in pediatric auditory brainstem implant surgery

OBJECTIVE

Electrically evoked auditory brainstem responses (EABR) guide placement of the multichannel auditory brainstem implant (ABI) array during surgery. EABRs are also recorded under anesthesia in nontumor pediatric ABI recipients prior to device activation to confirm placement and guide device programming. We examine the influence of anesthesia on evoked response morphology in pediatric ABI users by comparing intraoperative with postoperative EABR recordings.

STUDY DESIGN

Retrospective review.

METHODS

Seven children underwent ABI surgery by way of retrosigmoid craniotomy. General anesthesia included inhaled sevoflurane induction and propofol maintenance during which EABRs were recorded to confirm accurate positioning of the ABI. A mean of 7.7 ± 2.8 weeks following surgery, the ABI was activated under general anesthesia or sedation (dexmedetomidine) and EABR recordings were made. A qualitative analysis of intraoperative and postoperative waveform morphology was performed.

RESULTS

Seven subjects (mean age 20.6 months) underwent nine ABI surgeries (seven primary, two revisions) and nine activations. EABRs were observed in eight of nine postoperative recordings. In three cases, intraoperative EABRs during general anesthesia were similar to postoperative EABRs with sedation. In one case, sevoflurane and propofol were used for intra- and postoperative recordings, and waveforms were also similar. In four cases, amplitude and latency changes were observed for intraoperative versus postoperative EABRs.

CONCLUSION

Similarity of EABR morphology in the anesthetized versus sedated condition suggests that anesthesia does not have a large effect on far-field evoked potentials. Changes in EABR waveform morphology observed postoperatively may be influenced by other factors such as movements of the surface array.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:507-513, 2020.

Use of Research Interfaces for Psychophysical Studies With Cochlear-Implant Users

A growing number of laboratories are using research interfaces to conduct experiments with cochlear-implant (CI) users. Because these interfaces bypass a subject’s clinical sound processor, several concerns exist regarding safety and stimulation levels. Here we suggest best-practice approaches for how to safely and ethically perform this type of research and highlight areas of limited knowledge where further research is needed to help clarify safety limits. The article is designed to provide an introductory level of technical detail about the devices and the effects of electrical stimulation on perception and neurophysiology. From this, we summarize what should be the best practices in the field, based on the literature and our experience. Findings from the review of the literature suggest that there are three main safety concerns: (a) to prevent biological or neural damage, (b) to avoid presentation of uncomfortably loud sounds, and (c) to ensure that subjects have control over stimulus presentation. Researchers must pay close attention to the software–hardware interface to ensure that the three main safety concerns are closely monitored. An important area for future research will be the determination of the amount of biological damage that can occur from electrical stimulation from a CI placed in the cochlea, not in direct contact with neural tissue. As technology used in research with CIs evolve, some of these approaches may change. However, the three main safety principles outlined here are not anticipated to undergo change with technological advances.

Auditory brainstem implant in postmeningitis totally ossified cochleae

INTRODUCTION

An auditory brainstem implant (ABI) is an option for auditory rehabilitation in patients with totally ossified cochleae who cannot receive a conventional cochlear implant.

OBJECTIVE

To evaluate the outcomes in audiometry and speech perception tests after the implantation of an ABI via the extended retrolabyrinthine approach in patients with postmeningitis hearing loss.

MATERIALS AND METHODS

Ten patients, including children and adults, with postmeningitis hearing loss and bilateral totally ossified cochleae received an ABI in a tertiary center from 2009 to 2015. The extended retrolabyrinthine approach was performed in all the patients by the same surgeons. A statistical analysis compared pure tonal averages and speech perception tests before and at least 12 months after the ABI activation.

RESULTS

Eight patients (80%) showed improvements in tonal audiometry and the word and vowel perception tests after an average follow-up of 3.3 years. Two patients recognized up to 40% of the closed-set sentences without lip-reading. Two patients had no auditory response.

CONCLUSIONS

The ABI improved hearing performance in audiometry and speech perception tests in cases of postmeningitis hearing loss. The extended retrolabyrinthine approach is a safe surgical option for patients with postmeningitis hearing loss and bilateral totally ossified cochleae.

Early Communication Development of Children with Auditory Brainstem Implants

The auditory brainstem implant (ABI) is an auditory sensory device that is surgically placed on the cochlear nucleus of the brainstem for individuals who are deaf but unable to benefit from a cochlear implant (CI) due to anatomical abnormalities of the cochlea and/or eighth nerve, specific disease processes, or temporal bone fractures. In the United States, the Food and Drug Administration has authorized a Phase I clinical trial to determine safety and feasibility of the ABI in up to 10 eligible young children who are deaf and either derived no benefit from the CI or were anatomically unable to receive a CI. In this paper, we describe the study protocol and the children who have enrolled in the study thus far. In addition, we report the scores on speech perception, speech production, and language (spoken and signed) for five children with 1-3 years of assessment post-ABI activation. To date, the results indicate that spoken communication skills are slow to develop and that visual communication remains essential for post-ABI intervention.

Recent surgical options for vestibular vertigo

Vertigo is not a well-defined disease but a symptom that can occur in heterogeneous entities diagnosed and treated mainly by otolaryngologists, neurologists, internal medicine, and primary care physicians. Most vertigo syndromes have a good prognosis and management is predominantly conservative, whereas the need for surgical therapy is rare, but for a subset of patients often the only remaining option. In this paper, we describe and discuss different surgical therapy options for hydropic inner ear diseases, Menière's disease, dehiscence syndromes, perilymph fistulas, and benign paroxysmal positional vertigo. At the end, we shortly introduce the most recent developments in regard to vestibular implants. Surgical therapy is still indicated for vestibular disease in selected patients nowadays when conservative options did not reduce symptoms and patients are still suffering. Success depends on the correct diagnosis and choosing among different procedures the ones going along with an adequate patient selection. With regard to the invasiveness and the possible risks due to surgery, in depth individual counseling is absolutely necessary. Ablative and destructive surgical procedures usually achieve a successful vertigo control, but are associated with a high risk for hearing loss. Therefore, residual hearing has to be included in the decision making process for surgical therapy.

Long-term Results of ABI in Children With Severe Inner Ear Malformations

OBJECTIVE

To report the long-term outcomes of children who received auditory brainstem implant (ABI) because of severe inner ear malformations.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral otolaryngology clinic.

SUBJECTS AND METHODS

Between July 2006 and October 2014, 60 children received ABI at Hacettepe University. Preoperative work up included otolaryngologic examination, audiological assessment, radiological evaluation together with assessment of language development and psychological status. The surgeries were performed via retrosigmoid approach with a pediatric neurosurgeon. Intraoperatively, electrical auditory brainstem response was utilized. Initial stimulation was done 4 to 5 weeks postoperatively. Outcomes were evaluated with Categories of Auditory Performance (CAP), speech intelligibility rate (SIR), functional auditory performance of cochlear implant (FAPCI) and Manchester Spoken Language Development Scale scores; receptive and expressive language ages were determined.

RESULTS

Sixty children who received ABI were between ages of 12 and 64 months. Thirty-five patients with follow up period of at least 1 year, were reported in means of long-term audiological and language results. The most prevelant inner ear malformation was cochlear hypoplasia (n = 19). No major complication was encountered. Majority of the patients were in CAP 5 category, which implies that they can understand common phrases without lip reading. SIR was found out to be better with improving hearing thresholds. Children with ABI were performing worse than average cochlear implantation (CI) users when FAPCI scores were compared. Patients with the best hearing thresholds have expressive vocabulary of 50 to 200 words when evaluated with Manchester Spoken Language Development Scale. There was no relationship between the number of active electrodes and hearing thresholds. The type of inner ear anomaly with the best and the worst hearing thresholds were common cavity and cochlear aperture aplasia, respectively. Patients with additional handicaps had worse outcomes. Among 35 children, 29 had closed set discrimination and 12 developed open set discrimination above 50%. It was determined that, progress of the patients is faster in the initial 2 years when compared with further use of ABI.

CONCLUSION

ABI is an acceptable and effective treatment modality for pediatric population with severe inner ear malformations. Bilateral stimulation together with CI and contralateral ABI should be utilized in suitable cases.

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.

Biofunctionalized peptide-based hydrogels provide permissive scaffolds to attract neurite outgrowth from spiral ganglion neurons

Cochlear implants (CI) allow for hearing rehabilitation in patients with sensorineural hearing loss or deafness. Restricted CI performance results from the spatial gap between spiral ganglion neurons and the CI, causing current spread that limits spatially restricted stimulation and impairs frequency resolution. This may be substantially improved by guiding peripheral processes of spiral ganglion neurons towards and onto the CI electrode contacts. An injectable, peptide-based hydrogel was developed which may provide a permissive scaffold to facilitate neurite growth towards the CI. To test hydrogel capacity to attract spiral ganglion neurites, neurite outgrowth was quantified in an in vitro model using a custom-designed hydrogel scaffold and PuraMatrix^®. Neurite attachment to native hydrogels is poor, but significantly improved by incorporation of brain-derived neurotrophic factor (BDNF), covalent coupling of the bioactive laminin epitope IKVAV and the incorporation a full length laminin to hydrogel scaffolds. Incorporation of full length laminin protein into a novel custom-designed biofunctionalized hydrogel (IKVAV-GGG-SIINFEKL) allows for neurite outgrowth into the hydrogel scaffold. The study demonstrates that peptide-based hydrogels can be specifically biofunctionalized to provide a permissive scaffold to attract neurite outgrowth from spiral ganglion neurons. Such biomaterials appear suitable to bridge the spatial gap between neurons and the CI.

Experiences from Auditory Brainstem Implantation (ABIs) in four paediatric patients

INTRODUCTION

Indications for auditory brainstem implants (ABIs) have been widened from patients with neurofibromatosis type 2 (NF2) to paediatric patients with congenital cochlear malformations, cochlear nerve hypoplasia/aplasia, or cochlear ossification after meningitis. We present four ABI surgeries performed in children at Uppsala University Hospital in Sweden since 2009.

METHODS

Three children were implanted with implants from Cochlear Ltd. (Lane Cove, Australia) and one child with an implant from MedEl GMBH (Innsbruck, Austria). A boy with Goldenhar syndrome was implanted with a Cochlear Nucleus ABI24M at age 2 years (patient 1). Another boy with CHARGE syndrome was implanted with a Cochlear Nucleus ABI541 at age 2.5 years (patient 2). Another boy with post-ossification meningitis was implanted with a Cochlear Nucleus ABI24M at age 4 years (patient 3). A girl with cochlear aplasia was implanted with a MedEl Synchrony ABI at age 3 years (patient 4). In patients 1, 2, and 3, the trans-labyrinthine approach was used, and in patient 4 the retro-sigmoid approach was used.

RESULTS

Three of the four children benefited from their ABIs and use it full time. Two of the full time users had categories of auditory performance (CAP) score of 4 at their last follow up visit (6 and 2.5 years postoperative) which means they can discriminate consistently any combination of two of Ling's sounds. One child has not been fully evaluated yet, but is a full time user and had CAP 2 (responds to speech sounds) after 3 months of ABI use. No severe side or unpleasant stimulation effects have been observed so far. There was one case of immediate electrode migration and one case of implant device failure after 6.5 years.

CONCLUSION

ABI should be considered as an option in the rehabilitation of children with similar diagnoses.

Self-reported benefit, sound perception, and quality-of-life in patients with auditory brainstem implants (ABIs)

CONCLUSION

The majority of the patients used their auditory brainstem implants (ABIs) all the time, reporting that he/she would make the decision to receive an implant again if the decision were reconsidered. The findings support that the ABI is a valuable treatment in patients with type 2 neurofibromatosis (NF2) and in children with congenital inner ear and nerve anomalies or cochlear ossification.

OBJECTIVE

To evaluate the patients who underwent ABI implantation in Uppsala during 1993-2013. This study analyzed patients' implant use, perception of environmental sounds, perceived benefit from the implant, and quality-of-life (QoL).

METHOD

The NF2-patients (n = 20) comprised the majority of the patients, and there were a few non-NF2 pediatric patients (n = 4). The exclusion criteria included deceased patients (n = 4) and patients with no hearing sensations from the implant, or those with an inactivated ABI (n = 2). The data were collected from a questionnaire survey.

RESULTS

Eleven adult patients and two pediatric patients answered the questionnaires. Eight of the adult patients used their implants 'always'. The two children always used their implants. Hearing problems had the largest negative effect on the QoL. The non-users and the users scored equally on the NFTI-QoL.