Delayed Auditory Brainstem Responses in Prelingually Deaf and Late-Implanted Cochlear Implant Users

Neurophysiological studies in animals and humans suggest that severe hearing loss during early development impairs the maturation of the auditory brainstem. To date, studies in humans have mainly focused on the neural activation of the auditory brainstem in children treated with a cochlear implant (CI), but little is known about the pattern of activation in adult CI users with early onset of deafness (prelingual, before the age of 2 years). In this study, we compare auditory brainstem activation in prelingually deaf and late-implanted adult CI users to that in postlingually deaf CI users. Electrically evoked auditory brainstem responses (eABRs) were recorded by monopolar stimulation, separately using a middle and an apical electrode of the CI. Comparison of the eABR latencies revealed that wave V was significantly delayed in the prelingually deaf CI users on both electrode locations. Accordingly, when the apical electrode was stimulated, the III–V interwave interval was significantly longer in the prelingually deaf group. These findings suggest a slower neural conduction in the auditory brainstem, probably caused by impairment of maturation during the long duration of severe hearing loss in infancy. Shorter wave V latencies, reflecting a more mature brainstem, appeared to be a predictor for better speech perception.     

Cortical auditory evoked potential (CAEP) and behavioural measures of auditory function in a child with a single-sided deafness

Objectives: To study the changes in behavioural and cortical responses over time in a child with single-sided deafness fitted with a cochlear implant (CI).

Methods: Cortical auditory evoked potentials (CAEPs) in noise (+5?dB signal-to-noise ratio) were recorded and auditory skills were assessed using tests of sound localization, spatial speech perception in noise, and self-ratings of auditory abilities (Listening inventory for education, LIFE and Speech, spatial and qualities of hearing questionnaire, SSQ parental version). Measures were obtained prior to and after a CI fitting, including one, six, and 12 months after the CI switch on.

Results: Spatial speech recognition improved over time. At 12 months post-CI, word recognition scores were similar to those of normal hearing children. Signal-to-noise ratios for sentences decreased (i.e. improved) over time post-CI. Sound localization markedly improved at 12 months post-CI compared to baseline. Self-perception of difficulty scores decreased over time. Parental ratings of hearing abilities improved compared to baseline for all subscales. There were changes in the P1–N1–P2 complex at 12 months post-CI, which were clearer frontally across stimuli. Further research is needed to understand the significance of such changes after CI fitting for single-sided deafness.

Conclusion: Although the changes observed could reflect maturational changes, the clinically significant improvement in recognition of speech in noise and improved questionnaire results suggest that the CI was beneficial, consistent with the feedback from the participant.     

Effect of Pulse Rate and Polarity on the Sensitivity of Auditory Brainstem and Cochlear Implant Users to Electrical Stimulation

To further understand the response of the human brainstem to electrical stimulation, a series of experiments compared the effect of pulse rate and polarity on detection thresholds between auditory brainstem implant (ABI) and cochlear implant (CI) patients. Experiment 1 showed that for 400-ms pulse trains, ABI users’ thresholds dropped by about 2 dB as pulse rate was increased from 71 to 500 pps, but only by an average of 0.6 dB as rate was increased further to 3500 pps. This latter decrease was much smaller than the 7.7-dB observed for CI users. A similar result was obtained for pulse trains with a 40-ms duration. Furthermore, experiment 2 showed that the threshold difference between 500- and 3500-pps pulse trains remained much smaller for ABI than for CI users, even for durations as short as 2 ms, indicating the effect of a fast-acting mechanism. Experiment 3 showed that ABI users’ thresholds were lower for alternating-polarity than for fixed-polarity pulse trains, and that this difference was greater at 3500 pps than at 500 pps, consistent with the effect of pulse rate on ABI users’ thresholds being influenced by charge interactions between successive biphasic pulses. Experiment 4 compared thresholds and loudness between trains of asymmetric pulses of opposite polarity, in monopolar mode, and showed that in both cases less current was needed when the anodic, rather than the cathodic, current was concentrated into a short time interval. This finding is similar to that previously observed for CI users and is consistent with ABI users being more sensitive to anodic than cathodic current. We argue that our results constrain potential explanations for the differences in the perception of electrical stimulation by CI and ABI users, and have potential implications for future ABI stimulation strategies.     

Enhanced Survival of Spiral Ganglion Cells After Cessation of Treatment with Brain-Derived Neurotrophic Factor in Deafened Guinea Pigs

Exogenous delivery of neurotrophic factors into the cochlea of deafened animals rescues spiral ganglion cells (SGCs) from degeneration. To be clinically relevant for human cochlear implant candidates, the protective effect of neurotrophins should persist after cessation of treatment and the treated SGCs should remain functional. In this study, the survival and functionality of SGCs were investigated after temporary treatment with brain-derived neurotrophic factor (BDNF). Guinea pigs in the experimental group were deafened, and 2 weeks later, the right cochleae were implanted with an electrode array and drug delivery cannula. BDNF was administered to the implanted cochleae during a 4-week period via a mini-osmotic pump. After completion of the treatment, the osmotic pumps were removed. Two weeks later, the animals were killed and the survival of SGCs was analyzed. To monitor the functionality of the auditory nerve, electrically evoked auditory brainstem responses (eABRs) were recorded in awake animals throughout the experiment. BDNF treatment resulted in enhanced survival of SGCs 2 weeks after cessation of the treatment and prevented the decreases in size and circularity that are seen in the untreated contralateral cochleae. The amplitude of the suprathreshold eABR response in BDNF-treated animals was significantly larger than in deafened control animals and comparable to that in normal-hearing control animals. The amplitude in the BDNF-treated group did not decrease significantly after cessation of treatment. The eABR latency in BDNF-treated animals was longer than normal and comparable to that in deafened control animals. These morphological and functional findings demonstrate that neurotrophic intervention had a lasting effect, which is promising for future clinical application of neurotrophic factors in implanted human cochleae.     

人工耳蜗植入者电听性脑干反应测试

目的　通过对人工耳蜗植入者的电听性脑干反应 (electricallyevokedauditorybrainstemresponses,EABR)检测 ,探讨术后患者的电听觉传导通路的功能状态和EABR阈值。方法　对 6例人工耳蜗植入患者术后进行EABR检测。分别选取近耳蜗底转、中部和近蜗顶部三个固定部位的蜗内电极作为刺激电极 ,进行EABR记录 ,将所测EABR阈值与主观阈值和NRT(neuralresponsetelemetry)阈值进行比较。结果　 6例患者 ,用 175电流级 (currentlevel)的刺激强度 ,每一部位都可记录到清晰易识别、重复性良好的EABR波形 ,在耳蜗底转 ,中部和蜗顶部电极测得EABR波Ⅲ平均潜伏期分别为 1.83± 0 .19、1.80± 0 .18、1.6 8± 0 .2 3ms ,波Ⅴ平均潜伏期分别为 3.90± 0 .16、3.74±0 .18、3.6 2± 0 .2 4ms;测得EABR平均阈值分别为 16 5 .33± 7.6 6、16 2 .6 7± 7.2 8、15 3.33± 8.0 2电流级。结论　EABR是了解人工耳蜗植入者听觉传导功能的存在及测定人工耳蜗植入术后听觉阈值的客观方法之一     

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.     

Effects of Pulse Phase Duration and Location of Stimulation Within the Inferior Colliculus on Auditory Cortical Evoked Potentials in a Guinea Pig Model

The auditory midbrain implant (AMI), which consists of a single shank array designed for stimulation within the central nucleus of the inferior colliculus (ICC), has been developed for deaf patients who cannot benefit from a cochlear implant. Currently, performance levels in clinical trials for the AMI are far from those achieved by the cochlear implant and vary dramatically across patients, in part due to stimulation location effects. As an initial step towards improving the AMI, we investigated how stimulation of different regions along the isofrequency domain of the ICC as well as varying pulse phase durations and levels affected auditory cortical activity in anesthetized guinea pigs. This study was motivated by the need to determine in which region to implant the single shank array within a three-dimensional ICC structure and what stimulus parameters to use in patients. Our findings indicate that complex and unfavorable cortical activation properties are elicited by stimulation of caudal–dorsal ICC regions with the AMI array. Our results also confirm the existence of different functional regions along the isofrequency domain of the ICC (i.e., a caudal–dorsal and a rostral–ventral region), which has been traditionally unclassified. Based on our study as well as previous animal and human AMI findings, we may need to deliver more complex stimuli than currently used in the AMI patients to effectively activate the caudal ICC or ensure that the single shank AMI is only implanted into a rostral–ventral ICC region in future patients.     

Topography of Auditory Nerve Projections to the Cochlear Nucleus in Cats after Neonatal Deafness and Electrical Stimulation by a Cochlear Implant

We previously reported that auditory nerve projections from the cochlear spiral ganglion (SG) to the cochlear nucleus (CN) exhibit clear cochleotopic organization in adult cats deafened as neonates before hearing onset. However, the topographic specificity of these CN projections in deafened animals is proportionately broader than normal (less precise relative to the CN frequency gradient). This study examined SG-to-CN projections in adult cats that were deafened as neonates and received a unilateral cochlear implant at approximately 7 weeks of age. Following several months of electrical stimulation, SG projections from the stimulated cochleae were compared to projections from contralateral, non-implanted ears. The fundamental organization of SG projections into frequency band laminae was clearly evident, and discrete projections were always observed following double SG injections in deafened cochleae, despite severe auditory deprivation and/or broad electrical activation of the SG. However, when normalized for the smaller CN size after deafness, AVCN, PVCN, and DCN projections on the stimulated side were broader by 32%, 34%, and 53%, respectively, than projections in normal animals (although absolute projection widths were comparable to normal). Further, there was no significant difference between projections from stimulated and contralateral non-implanted cochleae. These findings suggest that early normal auditory experience may be essential for normal development and/or maintenance of the topographic precision of SG-to-CN projections. After early deafness, the CN is smaller than normal, the topographic distribution of these neural projections that underlie frequency resolution in the central auditory system is proportionately broader, and projections from adjacent SG sectors are more overlapping. Several months of stimulation by a cochlear implant (beginning at approximately 7 weeks of age) did not lessen or exacerbate these degenerative changes observed in adulthood. One clinical implication of these findings is that congenitally deaf cochlear implant recipients may have central auditory system alterations that limit their ability to achieve spectral selectivity equivalent to post-lingually deafened subjects.     

人工耳蜗植入者EABR、NRT与ESR检测

目的探讨应用客观检测方法评价人工耳蜗植入患者术后听觉传导功能并指导术后调试的可行性。方法对39名人工耳蜗植入者分别选取第3、10、20电极,进行电诱发听性脑干反应(electric allyevok edaudito rybrainstem responses,EABR)、神经反应遥测(neuralresponset elemetry,NRT)、电刺激镫骨肌反射(electricall yevokedstap ediusresponses,ESR)检测及主观心理物理测试,测定EABR、电诱发听神经复合动作电位(electricallyevokedcompoundactionpotentials,ECAP)、ESR阈值、主观阈值(T-levels)和主观最大舒适强度(C-levels),分别对EABR、ECAP阈值与主观阈值,ESR阈值与主观最大舒适强度进行相关性研究。结果EABR平均阈值分别为158.63±10.86、159.71±11.17、152.92±10.82电流级(currentlevel,CL);ECAP平均阈值分别为188.71±15.19、194.61±10.21、185.07±11.52CL;ESR平均阈值分别为210.10±16.16、209.81±14.24、204.55±12.90CL。EABR阈值与主观阈值间、ESR阈值与最大舒适强度间显著相关(P<0.01);ECAP阈值与主观阈值间无显著相关性(P>0.05)。结论EABR是判断人工耳蜗植入者听觉传导功能的有效客观方法;EABR和ESR阈值的测定可协助判断人工耳蜗植入者的主观阈值和最大舒适强度。     

Effects of Brain-Derived Neurotrophic Factor (BDNF) and Electrical Stimulation on Survival and Function of Cochlear Spiral Ganglion Neurons in Deafened, Developing Cats

Both neurotrophic support and neural activity are required for normal postnatal development and survival of cochlear spiral ganglion (SG) neurons. Previous studies in neonatally deafened cats demonstrated that electrical stimulation (ES) from a cochlear implant can promote improved SG survival but does not completely prevent progressive neural degeneration. Neurotrophic agents combined with an implant may further improve neural survival. Short-term studies in rodents have shown that brain-derived neurotrophic factor (BDNF) promotes SG survival after deafness and may be additive to trophic effects of stimulation. Our recent study in neonatally deafened cats provided the first evidence of BDNF neurotrophic effects in the developing auditory system over a prolonged duration Leake et al. (J Comp Neurol 519:1526–1545, 2011). Ten weeks of intracochlear BDNF infusion starting at 4 weeks of age elicited significant improvement in SG survival and larger soma size compared to contralateral. In the present study, the same deafening and BDNF infusion procedures were combined with several months of ES from an implant. After combined BDNF + ES, a highly significant increase in SG numerical density (>50 % improvement re: contralateral) was observed, which was significantly greater than the neurotrophic effect seen with ES-only over comparable durations. Combined BDNF + ES also resulted in a higher density of myelinated radial nerve fibers within the osseous spiral lamina. However, substantial ectopic and disorganized sprouting of these fibers into the scala tympani also occurred, which may be deleterious to implant function. EABR thresholds improved (re: initial thresholds at time of implantation) on the chronically stimulated channels of the implant. Terminal electrophysiological studies recording in the inferior colliculus (IC) revealed that the basic cochleotopic organization was intact in the midbrain in all studied groups. In deafened controls or after ES-only, lower IC thresholds were correlated with more selective activation widths as expected, but no such correlation was seen after BDNF + ES due to much greater variability in both measures.     

Cortical plasticity in the first year after cochlear implantation

Abstract

This study aimed to investigate changes in auditory and visual cortical activity over the first year following cochlear implantation using ¹⁸F-fluorodeoxyglucose positron emission tomography. Subjects underwent scanning prior to the initial implant activation (control), after one to two months of implant use (early activation) and after one year of implant use (late activation). All subjects had activation of the auditory cortices. Group analysis using Statistical Parametric Mapping package SPM99 showed these became more focused over the first year of implant use. There was no evidence of left hemispheric dominance at any stage post implantation.

Visual cortical activations were highly variable between patients and did not increase significantly between early and late activations. Taken together, our results lead us to suggest that the neural processes that occur during the first year of auditory rehabilitation following cochlear implantation vary between individuals to a greater extent than previously reported. Copyright © 2008 John Wiley & Sons, Ltd.     

Cochlear implantation in patients with auditory neuropathy of varied etiologies

OBJECTIVES/HYPOTHESIS: Auditory neuropathy is a relatively recently described pattern of hearing loss characterized by preservation of outer hair cell function despite absent brainstem auditory evoked responses. Intact outer hair cell function is demonstrated by the presence of otoacoustic emissions and/or a measurable cochlear microphonic on electrocochleography, whereas no synchronous neural activity (absent action potentials) is seen on acoustically evoked brainstem auditory evoked response testing. The study reviews the authors' experience with six patients diagnosed with auditory neuropathy, four of whom have undergone cochlear implantation. MATERIALS AND METHODS: A retrospective review of all medical and audiological charts at the University of Virginia Hospitals (Charlottesville, VA) was performed to identify patients who have undergone cochlear implantation or have been diagnosed with auditory neuropathy, or both. RESULTS: Six patients with hearing loss attributable to auditory neuropathy were identified, four of whom have undergone cochlear implantation. Causes varied, including congenital, infectious, and idiopathic origins. Adults demonstrated subjective auditory perception on promontory stimulation, whereas no repeatable brainstem auditory evoked response waveforms could be demonstrated on pediatric promontory stimulation testing. Patients with implants demonstrated implant-evoked brainstem auditory evoked responses and improved audiological performance. CONCLUSIONS: The six cases presented in the study represent varied causes and, probably, varied sites of lesions of auditory neuropathy. Promontory stimulation has been valuable, particularly in adults. Cochlear implantation allows the opportunity to provide a supraphysiological electrical stimulation to the auditory nerve, with the hope of reintroducing synchronous neural activity. Greater confidence and enthusiasm for cochlear implantation in appropriately selected patients with auditory neuropathy are gained through experience with such diverse cases.     

皮层听觉诱发电位评估人工耳蜗植入语前聋儿童的中枢听觉系统发育

目的研究人工耳蜗植入语前聋儿童的皮层听觉诱发电位(cortical auditory evoked potential,CAEP)P1波潜伏期的发展规律,评估不同年龄段植入人工耳蜗语前聋儿童的中枢听觉系统的发育。方法以人工耳蜗植入语前聋儿童50例(植入年龄15~66月,平均38.7±15.2月,其中小于42月龄者27例,大于42月龄者23例)和年龄相匹配的正常听力儿童50例为研究对象,采用500、1000、2000、4000 Hz四种频率的短纯音(tone burst,TB)刺激声分别对受试者进行皮层听觉诱发电位测试,并对人工耳蜗植入语前聋儿童进行婴幼儿有意义听觉整合量表或有意义听觉整合量表(infant-toddler meaningful auditory integration scale/meamingful auditory integration scale,IT-MAIS/MAIS)评分,比较两组P1波潜伏期,对P1波潜伏期和IT-MAIS/MAIS评分进行相关性分析。结果正常听力儿童四种不同频率短纯音刺激记录的CAEP P1波潜伏期与年龄均呈负相关(P<0.01);42月龄前植入人工耳蜗的语前聋儿童P1波潜伏期与正常听力儿童无统计学差异(P>0.05);42月龄以后植入人工耳蜗的语前聋儿童的P1波潜伏期较正常儿童显著延长,差异有显著统计学意义(P<0.01)。人工耳蜗植入儿童的CAEP P1波潜伏期与IT-MAIS/MAIS量表评分均呈负相关(P<0.01),不同频率TB刺激声下的P1波潜伏期无统计学差异(P>0.05)。结论大于42月龄植入人工耳蜗的语前聋儿童的中枢听觉系统发育较正常听力儿童延迟。     

Residual Hair Cell Responses in Electric-Acoustic Stimulation Cochlear Implant Users with Complete Loss of Acoustic Hearing After Implantation

Changes in cochlear implant (CI) design and surgical techniques have enabled the preservation of residual acoustic hearing in the implanted ear. While most Nucleus Hybrid L24 CI users retain significant acoustic hearing years after surgery, 6–17 % experience a complete loss of acoustic hearing (Roland et al. Laryngoscope. 126(1):175-81. (2016), Laryngoscope. 128(8):1939-1945 (2018); Scheperle et al. Hear Res. 350:45-57 (2017)). Electrocochleography (ECoG) enables non-invasive monitoring of peripheral auditory function and may provide insight into the pathophysiology of hearing loss. The ECoG response is evoked using an acoustic stimulus and includes contributions from the hair cells (cochlear microphonic—CM) as well as the auditory nerve (auditory nerve neurophonic—ANN). Seven Hybrid L24 CI users with complete loss of residual hearing months after surgery underwent ECoG measures before and after loss of hearing. While significant reductions in CMs were evident after hearing loss, all participants had measurable CMs despite having no measurable acoustic hearing. None retained measurable ANNs. Given histological data suggesting stable hair cell and neural counts after hearing loss (e.g., Quesnel et al. Hear Res. 333:225-234. (2016)), the loss of ECoG and audiometric hearing may reflect reduced synaptic input. This is consistent with the theory that residual CM responses coupled with little to no ANN responses reflect a “disconnect” between hair cells and auditory nerve fibers (Fontenot et al. Ear Hear. 40(3):577-591. 2019). This “disconnection” may prevent proper encoding of auditory stimulation at higher auditory pathways, leading to a lack of audiometric responses, even in the presence of viable cochlear hair cells.     

Barriers to Cochlear Implant Access: Acknowledging the Challenges,Changing the Future: Barriers to Adult Cochlear Implant Care in the United States: An Analysis of Health Care Delivery

Persistent underutilization of cochlear implants (CIs) in the United States is in part a reflection of a lack of hearing health knowledge and the complexities of care delivery in the treatment of sensorineural hearing loss. An evaluation of the patient experience through the CI health care delivery process systematically exposes barriers that must be overcome to undergo treatment for moderate-to-severe hearing loss. This review analyzes patient-facing obstacles including diagnosis of hearing loss, CI candidate identification and referral to surgeon, CI evaluation and candidacy criteria interpretation, and lastly CI surgery and rehabilitation. Pervasive throughout the process are several themes which demand attention in addressing inequities in hearing health disparities in the United States.     

Auditory Cortical Activity During Cochlear Implant-Mediated Perception of Spoken Language, Melody, and Rhythm

Despite the significant advances in language perception for cochlear implant (CI) recipients, music perception continues to be a major challenge for implant-mediated listening. Our understanding of the neural mechanisms that underlie successful implant listening remains limited. To our knowledge, this study represents the first neuroimaging investigation of music perception in CI users, with the hypothesis that CI subjects would demonstrate greater auditory cortical activation than normal hearing controls. H₂ ¹⁵O positron emission tomography (PET) was used here to assess auditory cortical activation patterns in ten postlingually deafened CI patients and ten normal hearing control subjects. Subjects were presented with language, melody, and rhythm tasks during scanning. Our results show significant auditory cortical activation in implant subjects in comparison to control subjects for language, melody, and rhythm. The greatest activity in CI users compared to controls was seen for language tasks, which is thought to reflect both implant and neural specializations for language processing. For musical stimuli, PET scanning revealed significantly greater activation during rhythm perception in CI subjects (compared to control subjects), and the least activation during melody perception, which was the most difficult task for CI users. These results may suggest a possible relationship between auditory performance and degree of auditory cortical activation in implant recipients that deserves further study.     

Cochlear implant performance in children deafened by congenital cytomegalovirus—A systematic review

Background

Congenital cytomegalovirus (cCMV) infection is a major cause of sensorineural hearing loss in children.

Objective of review

The objective of this systematic review was to compare performance in paediatric cochlear implant users with SNHL caused by cCMV compared to non‐cCMV implantees.

Type of review

Systematic review

Search strategy

PubMed, EMBASE and the Cochrane databases were searched from inception up to 15 May 2017 for children, cochlear implant, performance and their synonyms.

Evaluation methods

Titles, abstracts and full texts were screened for eligibility. Directness of evidence and risk of bias were assessed. From the included studies, study characteristics and outcome data (speech perception, speech production, receptive language and auditory performance of cCMV groups and non‐cCMV groups) were extracted.

Results

A total of 5280 unique articles were screened of which 28 were eligible for critical appraisal. After critical appraisal, 12 studies remained for data extraction. Seven of 12 studies showed worse performance after cochlear implantation in cCMV children compared to non‐cCMV children. Worse performance in cCMV children was attributed to cCMV‐related comorbidities in six of these studies. Available data on asymptomatic cCMV children compared to non‐cCMV children did not reveal an unfavourable effect on cochlear implant performance.

Conclusions

The available evidence reveals that cCMV children often have worse cochlear implant performance compared to non‐cCMV children, which can be attributed to cCMV related comorbidities. We urge physicians to take into account the cCMV related comorbidities in the counselling of paediatric CI users deafened by cCMV.