Cochlear implants and other inner ear prostheses: today and tomorrow

Local delivery of steroids to inner ear via medical device INCAT (the Inner Ear Catheter) in partial deafness patients during cochlear implantation - preliminary results and a feasibility study

BACKGROUND

The primary aim was to assess the effectiveness and safety of three different algorithms of using steroids and inner ear catheter (INCAT) MED-EL® in partial deafness patients who underwent cochlear implantation. The secondary goal was the assessment of the impact of the depth of INCAT on hearing preservation after cochlear implantation.

RESEARCH DESIGN AND METHODS

There were three algorithms of steroid administration: 1) methylprednisolone 62.5 mg/ml (solution), 3 patients; 2) methylprednisolone 40 mg/ml (suspension), 4 patients; 3) dexamethasone 4 mg/ml (solution), 3 patients. Pure tone audiometry (0.125-8 kHz) was performed preoperatively, 1 and 6 months post-op. Hearing preservation was assessed according to the HEARRING group formula. Impedance measurements were taken at two days, 1 and 6 months after surgery.

RESULTS

Patients treated with methylprednisolone 40 mg/ml in suspension showed the best hearing preservation (50% complete and 50% partial preservation) 1 month post-op and later remained the most favorable. The lowest impedance was found in this group both 1 and 6 months post-op. A shorter INCAT insertion depth appeared to be more favorable than a longer one.

CONCLUSION

Our results suggest that patients treated with methylprednisolone 40 mg/ml (suspension) had better hearing outcomes compared to the other two medications.

Safety evaluations for transtympanic laser stimulation of the cochlea in Mongolian gerbils (Meriones unguiculatus)

Infrared laser stimulation of the cochlea has been proposed as a possible alternative to conventional auditory prostheses. Whereas previous studies have focused primarily on the short-term effects of laser stimulation, the practical application of this technics requires an investigation into whether prolonged laser exposure can induce neural responses and safely. This study assessed the effect of laser-induced damage to the cochlea on auditory perception using Mongolian gerbils (Meriones unguiculatus) trained with a classical conditioning task. The broadband noise was presented as a conditioned stimulus, and reward licking was recorded as a conditioned response. After training, the subject's cochlea was exposed to a continuous pulsed laser for 15 h. Broadband noise of various intensities was presented without pairing it with water before and after laser exposure to assess the decrease in auditory perception due to laser-induced injury. The licking rate did not change after laser exposure of 6.6 W/cm2 or weaker but drastically decreased after 26.4 W/cm2 or higher. These findings showed, for the first time, that the safety margin of long-term, at least several hours, cochlear laser stimulation exists and will contribute to the appropriate delimitation of the safe and effective laser stimulation parameters in future research.

Sentence Comprehension in Spanish-Speaking Children With Hearing Loss: On the Integration of Morphosyntactic and Lexico-Semantic Cues

PURPOSE

Children with hearing loss (CHL) who use hearing devices (cochlear implants or hearing aids) and communicate orally have trouble comprehending sentences with noncanonical order. This study explores sentence comprehension strategies in Spanish-speaking CHL, focusing on their ability to integrate morphosyntactic cues (word order, morphological case marking) with verbs differing in their syntax-to-semantics configuration.

METHOD

Fifty-eight Spanish-speaking CHL and 58 children with typical hearing (CTH) with a hearing age of 3;5-7;8 (years;months; i.e., time of adequate access to sound, in the case of CHL since effective fitting or implantation) were recruited in Argentina. A sentence comprehension task using the truth-value judgment paradigm was designed, including sentences with activity verbs and object-experiencer psych verbs in subject-verb-object (SVO) and object-verb-subject (OVS) orders, thus varying in canonicity.

RESULTS

Both groups showed good comprehension of SVO sentences with activity verbs but had difficulties with structures that deviated from canonicity. Comprehension was at chance level in both groups and at all hearing ages for sentences with activity verbs in OVS order and sentences with object-experiencer psych verbs in SVO order (both are noncanonical for the verb type). Sentences with object-experiencer psych verbs in OVS order were also comprehended at chance level by CHL and by the youngest CTH.

CONCLUSIONS

These results suggest that Spanish-speaking CTH aged 7 years prioritize semantic information over case marking in sentences with a noncanonical syntactic structure. In CHL, difficulties with noncanonical structures seem to extend to semantic deviations, at least until hearing age 7 years. CHL might also struggle with the semantic structures of object-experiencer psych verbs beyond the age when CTH do. These findings are relevant for the linguistic assessment and education of CHL.

Functional connectivity across the human subcortical auditory system using an autoregressive matrix-Gaussian copula graphical model approach with partial correlations

The auditory system comprises multiple subcortical brain structures that process and refine incoming acoustic signals along the primary auditory pathway. Due to technical limitations of imaging small structures deep inside the brain, most of our knowledge of the subcortical auditory system is based on research in animal models using invasive methodologies. Advances in ultrahigh-field functional magnetic resonance imaging (fMRI) acquisition have enabled novel noninvasive investigations of the human auditory subcortex, including fundamental features of auditory representation such as tonotopy and periodotopy. However, functional connectivity across subcortical networks is still underexplored in humans, with ongoing development of related methods. Traditionally, functional connectivity is estimated from fMRI data with full correlation matrices. However, partial correlations reveal the relationship between two regions after removing the effects of all other regions, reflecting more direct connectivity. Partial correlation analysis is particularly promising in the ascending auditory system, where sensory information is passed in an obligatory manner, from nucleus to nucleus up the primary auditory pathway, providing redundant but also increasingly abstract representations of auditory stimuli. While most existing methods for learning conditional dependency structures based on partial correlations assume independently and identically Gaussian distributed data, fMRI data exhibit significant deviations from Gaussianity as well as high-temporal autocorrelation. In this paper, we developed an autoregressive matrix-Gaussian copula graphical model (ARMGCGM) approach to estimate the partial correlations and thereby infer the functional connectivity patterns within the auditory system while appropriately accounting for autocorrelations between successive fMRI scans. Our results show strong positive partial correlations between successive structures in the primary auditory pathway on each side (left and right), including between auditory midbrain and thalamus, and between primary and associative auditory cortex. These results are highly stable when splitting the data in halves according to the acquisition schemes and computing partial correlations separately for each half of the data, as well as across cross-validation folds. In contrast, full correlation-based analysis identified a rich network of interconnectivity that was not specific to adjacent nodes along the pathway. Overall, our results demonstrate that unique functional connectivity patterns along the auditory pathway are recoverable using novel connectivity approaches and that our connectivity methods are reliable across multiple acquisitions.

Summating Potential as Marker of Intracochlear Position in Bipolar Electrocochleography

OBJECTIVES

Cochlear implantation criteria include subjects with residual low-frequency hearing. To minimize implantation trauma and to avoid unwanted interactions of electric- and acoustic stimuli, it is often recommended to stop cochlear implantation before the cochlear implant (CI) reaches the cochlear partition with residual hearing, as determined by an audiogram. For this purpose, the implant can be used to record acoustically evoked signals during implantation, including cochlear compound action potentials (CAP), cochlear microphonics (CMs), and summating potentials (SPs). The former two have previously been used to monitor residual hearing in clinical settings.

DESIGN

In the present study we investigated the use of intracochlear, bipolar SP recordings to determine the exact cochlear position of the contacts of implanted CIs in guinea pig cochleae (n = 13). Polarity reversals of SPs were used as a functional marker of intracochlear position. Micro computed tomography (µCT) imaging and a modified Greenwood function were used to determine the cochleotopic positions of the contacts in the cochlea. These anatomical reconstructions were used to validate the SP-based position estimates.

RESULTS

The precision of the SP-based position estimation was on average within ± 0.37 octaves and was not impaired by moderate hearing loss caused by noise exposure after implantation. It is important to note that acute hearing impairment did not reduce the precision of the method. The cochleotopic position of CI accounted for ~70% of the variability of SP polarity reversals. Outliers in the dataset were associated with lateral CI positions. Last, we propose a simplified method to avoid implantation in functioning parts of the cochlea by approaching a predefined frequency region using bipolar SP recordings through a CI.

CONCLUSIONS

Bipolar SP recordings provide reliable information on electrode position in the cochlea. The position estimate remains reliable after moderate hearing loss. The technique presented here could be applied during CI surgery to monitor the CI approach to a predefined frequency region.

The Clinical Effect of Steroids for Hearing Preservation in Cochlear Implantation: Conclusions Based on Three Cochlear Implant Systems and Two Administration Regimes

The main aim of this study was to assess the clinical effect of steroids (dexamethasone and prednisone) on hearing preservation in patients who underwent cochlear implantation with different cochlear implant systems (Oticon®, Advanced Bionics®, Med-El®). 147 adult patients met the inclusion criteria and were enrolled to the study and divided into three groups depending on the brand of cochlear implant they received and participated in all follow-up visits regularly. They were also randomly divided into three subgroups depending on the steroid administration regime: (1) intravenous dexamethasone (0.1 mg/kg body weight twice a day for three days); (2) combined intravenous and oral steroids (dexamethasone 0.1 mg/kg body weight twice a day plus prednisone 1 mg/kg weight once a day); and (3) no steroids (control group). The results were measured by pure tone audiometry (PTA) at three time points: (i) before implantation, (ii) at processor activation, and (iii) 12 months after activation. A hearing preservation (HP) figure was also calculated by comparing the preoperative results and the results after 12 months. Further measures collected were electrode impedance and hearing threshold in the non-operated ear. The highest HP measures (partial and complete) were obtained in the subgroups who were given steroids. Of the 102 patients given steroids, HP was partial or complete in 63 of them (62%). In comparison, partial or complete HP was achieved in only 15 patients out of 45 (33%) who were not given steroids. There were differences between the three cochlear implant groups, with the Med-El and Advanced Bionics groups performing better than the Oticon group (45% and 43% of the former two groups achieved partial or complete HP compared to 20% in the latter). Hearing thresholds in the non-operated ear were stable over 12 months. Generally, impedance was slightly lower in the 12 month follow-up in comparison with the activation period, with the exception of the Oticon group. (4) Conclusions: Pharmacological treatment with steroids in patients undergoing cochlear implantation helps to preserve residual hearing.

Development and Characterization of a Micromagnetic Alternative to Cochlear Implant Electrode Arrays

To stimulate the auditory nerve, cochlear implants directly inject electrical current into surrounding tissue via an implanted electrode array. While many cochlear implant users achieve strong speech perception scores, there remains significant variability. Since cochlear implant electrode arrays are surrounded by a conductive fluid, perilymph, a spread of excitation occurs. The functionality of the cochlea is spatially dependent, and a wider area of excitation negatively affects the hearing of the user. Importantly, magnetic fields are unaffected by the material properties of biological components. To utilize the electromagnetic properties of the human ear, a microcoil array was developed. The microcoils are 4-turn solenoids with a 250-μm turn radius and a 31.75-μm wire radius, coated with Parylene-C. The efficient design was implemented to accelerate testing. The obtained results describe stimulation capabilities. Functionality was validated using a frequency response analyzer to measure how the generated electromagnetic power radiates in space. 99.8% power loss was observed over a 100-μm separation between a pair of identical microcoils. Obtained through finite-element modeling, the microcoils can be driven by a 60 mA, 5 kHz, sinusoidal input for 10 minutes before predicted inflammation. Rattay's activating function was calculated to evaluate the magnetic stimulation effect of external fields on target neurons. Combined with the frequency response analysis, magnitude and spatial effects of the generated potential is established. As a result, each microcoil requires a 400-μm-wide area for each independent stimulation channel, which is 84% narrower than a commercial cochlear array channel, thereby suggesting greater spatial selectivity.

The Clinical Effect of Steroid Therapy on Preserving Residual Hearing after Cochlear Implantation with the Advanced Bionics HiRes Ultra 3D Cochlear Implant System

(1) Background: The main aim of this study was to assess the clinical effectiveness of two different schemes of administration of steroids ((1) dexamethasone administered intravenously in comparison with (2) combination of steroid treatments: orally administered prednisone and intravenously administered dexamethasone) in comparison with a control group (no steroid administration) on hearing preservation (HP) in patients who underwent an Advanced Bionics cochlear implantation. (2) Methods: Thirty-five adult patients met the inclusion criteria. All patients were randomly divided into three subgroups depending on the scheme of steroid administration: (1) the first subgroup with only intravenously administered dexamethasone (0.1 mg per kg body weight twice a day for three days), (2) the second subgroup with a combination of methods of administration of steroids (intravenous and oral steroid therapy (dexamethasone, 0.1 mg/kg body weight twice a day plus prednisone, 1 mg/kg weight once a day for three days before surgery and after administration of dexamethasone (4th, 5th, 6th day) and after this time the dose of prednisone was reduced)) and (3) the third subgroup without steroid therapy (control group). The results were measured by pure tone audiometry (PTA) in three periods: (1) before implantation, (2) during activation of the processor (one month after implantation), and (3) 12 months after activation. Patients’ hearing thresholds before implantation were on average 82 dB HL, 77 dB HL, and 88 dB HL, respectively. (3) Results: The majority of the patients from the first subgroup had hearing preserved partially (77.8%). A similar result was observed in the second study group (oral + i.v.) (partial hearing preservation was found in 61.5% of the participants). The opposite was true in the control group; a plurality of control patients (38.5%) had no measurable hearing 12 months after the activation of the processor. (4) Conclusions: Pharmacological treatment consisting of the administration of steroids in patients who had undergone cochlear implantation with the Advanced Bionics HiRes Ultra 3D cochlear implant system may be beneficial for preserving residual hearing in patients.

Usher syndrome IIIA: a review of the disorder and preclinical research advances in therapeutic approaches

Usher syndrome (USH) is an autosomal recessive disorder characterized by sensorineural hearing loss, progressive pigmentary retinopathy, and vestibular dysfunction. The degree and onset of hearing loss vary among subtypes I, II, and III, while blindness often occurs in the second to fourth decades of life. Usher type III (USH3), characterized by postlingual progressive sensorineural hearing loss, varying levels of vestibular dysfunction, and varying degrees of visual impairment, typically manifests in the first to second decades of life. While USH3 is rare, it is highly prevalent in certain populations. RP61, USH3, and USH3A symbolize the same disorder, with the latter symbol used more frequently in recent literature. This review focuses on the clinical features, epidemiology, molecular genetics, treatment, and research advances for sensory deficits in USH3A.

Advances in Pediatric and Adult Cochlear Implant and Middle Ear Prostheses

The aim of this special issue, entitled 'Advances in Pediatric and Adult Cochlear Implant and Middle Ear Prostheses', is to report the undergoing novel research in the area of ear prostheses, either for the middle or inner ear [...].

Electrical Signal Modeling in Cochlear Implants. Study of Temperature and Humidity Effects

The present paper discusses the climatic effects of humidity and temperature on cochlear implant functioning and the quality of the electrical sound signal. MATLAB Simulink simulations were prepared, offering insights into signal behavior under such climatic parameter changes. A simulation setup of the cochlear implant was developed, where a source type selection was used to change between a voice recording and a “chirp” sound. In addition, a DC blocking filter was applied to the input signal. A simulation code, with the application of the climatic influence via the air attenuation function, was developed. Thereby, the attenuation of temperature and humidity in the sound atmospheric circulation of the input signal, at T = 0 °C and RH = 0% and at T = 36 °C and RH = 40% was graphically represented. The results of the electrical pulse generator for each of the eight channels, with the IIR filter, Gaussian noise, temperature variation, humidity influence, and control of denoise block activity, were thus obtained.

The Clinical Effects of Steroids Therapy in the Preserving Residual Hearing after Cochlear Implantation with the OTICON Neuro Zti EVO

Background: A prospective clinical study was conducted to investigate whether two different pharmacotherapy strategies of steroid administration impact hearing preservation in adult patients who underwent cochlear implantation with the Oticon Medical Neuro cochlear implant system. Methods: Twenty nine adult participants were included. Pure tone audiometry was performed before implantation, during processor activation and 12 months after activation. There were three treatment groups: (1) intravenous steroid therapy (standard steroid therapy with dexamethasone administrated intravenously at the dose 0.1 mg/kg body mass twice a day); (2) combined oral and intravenous steroid therapy (extended steroid therapy with dexamethasone administrated intravenously at the dose 0.1 mg/kg b.m. twice a day and prednisone (orally) at the dose 1 mg/kg body mass/24 h), and (3) no steroid therapy (a control group). Patients’ hearing thresholds before implantation were on average 103 dB HL, 89 dB HL, and 93 dB HL, respectively. Results: Deterioration of hearing thresholds was observed in all three patients’ groups. Twelve months after surgery the patients with and without steroid therapy had similar hearing thresholds. Conclusions: The steroid regimen used in this study did not play a significant role in patients with non-functional residual hearing, who underwent cochlear implantation with the Oticon Medical Neuro cochlear implant system.