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Callejón-Leblic MA, Lazo-Maestre M, Fratter A, Ropero-Romero F, Sánchez-Gómez S, Reina-Tosina J. A full-head model to investigate intra and extracochlear electric fields in cochlear implant stimulation. Phys Med Biol 2024; 69:155010. [PMID: 38925131 DOI: 10.1088/1361-6560/ad5c38] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 06/26/2024] [Indexed: 06/28/2024]
Abstract
Objective.Despite the widespread use and technical improvement of cochlear implant (CI) devices over past decades, further research into the bioelectric bases of CI stimulation is still needed. Various stimulation modes implemented by different CI manufacturers coexist, but their true clinical benefit remains unclear, probably due to the high inter-subject variability reported, which makes the prediction of CI outcomes and the optimal fitting of stimulation parameters challenging. A highly detailed full-head model that includes a cochlea and an electrode array is developed in this study to emulate intracochlear voltages and extracochlear current pathways through the head in CI stimulation.Approach.Simulations based on the finite element method were conducted under monopolar, bipolar, tripolar (TP), and partial TP modes, as well as for apical, medial, and basal electrodes. Variables simulated included: intracochlear voltages, electric field (EF) decay, electric potentials at the scalp and extracochlear currents through the head. To better understand CI side effects such as facial nerve stimulation, caused by spurious current leakage out from the cochlea, special emphasis is given to the analysis of the EF over the facial nerve.Main results.The model reasonably predicts EF magnitudes and trends previously reported in CI users. New relevant extracochlear current pathways through the head and brain tissues have been identified. Simulated results also show differences in the magnitude and distribution of the EF through different segments of the facial nerve upon different stimulation modes and electrodes, dependent on nerve and bone tissue conductivities.Significance.Full-head models prove useful tools to model intra and extracochlear EFs in CI stimulation. Our findings could prove useful in the design of future experimental studies to contrast FNS mechanisms upon stimulation of different electrodes and CI modes. The full-head model developed is freely available for the CI community for further research and use.
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Affiliation(s)
- M A Callejón-Leblic
- Otorhinolaryngology Department, Virgen Macarena University Hospital, Seville 41009, Spain
- Oticon Medical, 28108 Madrid, Spain
- Dept. Signal Theory and Communications, Biomedical Engineering Group, University of Seville, Seville 41092, Spain
| | - M Lazo-Maestre
- Otorhinolaryngology Department, Virgen Macarena University Hospital, Seville 41009, Spain
| | - A Fratter
- Oticon Medical, 06220 Vallauris, France
| | - F Ropero-Romero
- Otorhinolaryngology Department, Virgen Macarena University Hospital, Seville 41009, Spain
| | - S Sánchez-Gómez
- Otorhinolaryngology Department, Virgen Macarena University Hospital, Seville 41009, Spain
| | - J Reina-Tosina
- Dept. Signal Theory and Communications, Biomedical Engineering Group, University of Seville, Seville 41092, Spain
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Tichacek O, Mistrík P, Jungwirth P. From the outer ear to the nerve: A complete computer model of the peripheral auditory system. Hear Res 2023; 440:108900. [PMID: 37944408 DOI: 10.1016/j.heares.2023.108900] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 10/03/2023] [Accepted: 10/23/2023] [Indexed: 11/12/2023]
Abstract
Computer models of the individual components of the peripheral auditory system - the outer, middle, and inner ears and the auditory nerve - have been developed in the past, with varying level of detail, breadth, and faithfulness of the underlying parameters. Building on previous work, we advance the modeling of the ear by presenting a complete, physiologically justified, bottom-up computer model based on up-to-date experimental data that integrates all of these parts together seamlessly. The detailed bottom-up design of the present model allows for the investigation of partial hearing mechanisms and their defects, including genetic, molecular, and microscopic factors. Also, thanks to the completeness of the model, one can study microscopic effects in the context of their implications on hearing as a whole, enabling the correlation with neural recordings and non-invasive psychoacoustic methods. Such a model is instrumental for advancing quantitative understanding of the mechanism of hearing, for investigating various forms of hearing impairment, as well as for devising next generation hearing aids and cochlear implants.
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Affiliation(s)
- Ondrej Tichacek
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nam. 2, 160 00 Prague 6, Czech Republic.
| | | | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nam. 2, 160 00 Prague 6, Czech Republic.
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van Gendt MJ, Koka K, Kalkman RK, Stronks HC, Briaire JJ, Litvak L, Frijns JHM. Simulating intracochlear electrocochleography with a combined model of acoustic hearing and electric current spread in the cochlea. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2020; 147:2049. [PMID: 32237816 DOI: 10.1121/10.0000948] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 03/06/2020] [Indexed: 06/11/2023]
Abstract
Intracochlear electrocochleography (ECochG) is a potential tool for the assessment of residual hearing in cochlear implant users during implantation and acoustical tuning postoperatively. It is, however, unclear how these ECochG recordings from different locations in the cochlea depend on the stimulus parameters, cochlear morphology, implant design, or hair cell degeneration. In this paper, a model is presented that simulates intracochlear ECochG recordings by combining two existing models, namely a peripheral one that simulates hair cell activation and a three-dimensional (3D) volume-conduction model of the current spread in the cochlea. The outcomes were compared to actual ECochG recordings from subjects with a cochlear implant (CI). The 3D volume conduction simulations showed that the intracochlear ECochG is a local measure of activation. Simulations showed that increasing stimulus frequency resulted in a basal shift of the peak cochlear microphonic (CM) amplitude. Increasing the stimulus level resulted in wider tuning curves as recorded along the array. Simulations with hair cell degeneration resulted in ECochG responses that resembled the recordings from the two subjects in terms of CM onset responses, higher harmonics, and the width of the tuning curve. It was concluded that the model reproduced the patterns seen in intracochlear hair cell responses recorded from CI-subjects.
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Affiliation(s)
- Margriet J van Gendt
- Department of Otorhinolaryngology, Leiden University Medical Centre, P.O Box 9600, 2300 RC Leiden, The Netherlands
| | - Kanthaiah Koka
- Research and Technology, Advanced Bionics, Valencia, California 91355, USA
| | - Randy K Kalkman
- Department of Otorhinolaryngology, Leiden University Medical Centre, P.O Box 9600, 2300 RC Leiden, The Netherlands
| | - H Christiaan Stronks
- Department of Otorhinolaryngology, Leiden University Medical Centre, P.O Box 9600, 2300 RC Leiden, The Netherlands
| | - Jeroen J Briaire
- Department of Otorhinolaryngology, Leiden University Medical Centre, P.O Box 9600, 2300 RC Leiden, The Netherlands
| | - Leonid Litvak
- Research and Technology, Advanced Bionics, Valencia, California 91355, USA
| | - Johan H M Frijns
- Department of Otorhinolaryngology, Leiden University Medical Centre, P.O Box 9600, 2300 RC Leiden, The Netherlands
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Al Abed A, Pinyon JL, Foster E, Crous F, Cowin GJ, Housley GD, Lovell NH. Computational Simulation Expands Understanding of Electrotransfer-Based Gene Augmentation for Enhancement of Neural Interfaces. Front Neurosci 2019; 13:691. [PMID: 31447624 PMCID: PMC6691069 DOI: 10.3389/fnins.2019.00691] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 06/18/2019] [Indexed: 12/16/2022] Open
Abstract
The neural interface is a critical factor in governing efficient and safe charge transfer between a stimulating electrode and biological tissue. The interface plays a crucial role in the efficacy of electric stimulation in chronic implants and both electromechanical properties and biological properties shape this. In the case of cochlear implants, it has long been recognized that neurotrophins can stimulate growth of the target auditory nerve fibers into a favorable apposition with the electrode array, and recently such arrays have been re-purposed to enable electrotransfer (electroporation)-based neurotrophin gene augmentation to improve the "bionic ear." For both this acute bionic array-directed electroporation and for chronic conventional cochlear implant arrays, the electric fields generated in target tissue during pulse delivery are central to efficacy, but are challenging to map. We present a computational model for predicting electric fields generated by array-driven DNA electrotransfer in the cochlea. The anatomically realistic model geometry was reconstructed from magnetic resonance images of the guinea pig cochlea and an eight-channel electrode array embedded within this geometry. The model incorporates a description of both Faradaic and non-Faradaic mechanisms occurring at the electrode-electrolyte interface with frequency dependency optimized to match experimental impedance spectrometry measurements. Our simulations predict that a tandem electrode configuration with four ganged cathodes and four ganged anodes produces three to fourfold larger area in target tissue where the electric field is within the range for successful gene transfer compared to an alternate paired anode-cathode electrode configuration. These findings matched in vivo transfection efficacy of a green fluorescent protein (GFP) reporter following array-driven electrotransfer of the reporter-encoding plasmid DNA. This confirms utility of the developed model as a tool to optimize the safety and efficacy of electrotransfer protocols for delivery of neurotrophin growth factors, with the ultimate aim of using gene augmentation approaches to improve the characteristics of the electrode-neural interfaces in chronically implanted neurostimulation devices.
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Affiliation(s)
- Amr Al Abed
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia
| | - Jeremy L Pinyon
- Translational Neuroscience Facility, Department of Physiology, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia
| | - Evelyn Foster
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia
| | - Frederik Crous
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia
| | - Gary J Cowin
- National Imaging Facility, Centre for Advanced Imaging, University of Queensland, Brisbane, QLD, Australia
| | - Gary D Housley
- Translational Neuroscience Facility, Department of Physiology, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia
| | - Nigel H Lovell
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia
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Christov F, Gluth MB, Lahti SJ, Ludwig S, Hans S, Holtmann LC, Lang S, Arweiler-Harbeck D. Electric compound action potentials (ECAPs) and impedances in an open and closed operative site during cochlear implantation. Cochlear Implants Int 2018; 20:23-30. [PMID: 30350745 DOI: 10.1080/14670100.2018.1534667] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
INTRODUCTION In patients undergoing cochlear implantation, intraoperative measures of impedance and electrically evoked compound action potentials (ECAPs) are used to confirm device integrity and electrode array position. However, these electrophysiological parameters have been shown to decrease over time, with a small decrement observable as early as 24 h post implantation and becoming more apparent after 6 months. Whether the intraoperatively measured impedances and ECAPs recorded immediately after electrode insertion versus later in the operation or in an open versus closed operative site vary has not been documented. Such variation in measurement procedure may affect the ultimate operative outcome. PATIENTS AND METHODS Between February and October 2016, 38 patients received a cochlear implant (Cochlear®), with half receiving a CI 522 device and the other half receiving a CI 512 device. These patients were distributed into three groups. In the first (group A; n = 21), the impedance and threshold neural response telemetry (tNRT) measures were taken before (M1) and after cutaneous suture (M2), whereas in the second group (group B; n = 11) they were taken twice in the open operative site, once at the time of electrode insertion (M1) and then again 10 min later (M2). The last group (group C; n = 6) was measured only once after a 10 min waiting time before closing the operative site. RESULTS tNRTs of both group A and B were significantly higher at M1 than measured at M2. The magnitude of change in tNRT did vary significantly by group (P = .027) with group A having a bigger decrease than group B. For impedances there was evidence for a significant difference in M2 between the three groups (P = .012), with group C having significantly higher values compared to group A and B. CONCLUSION Intraoperative tNRT measures change significantly over time, including within the first 10 min of implantation. One underlying etiology of this phenomenon for tNRTs seems to be the condition of the surgical site whereas changes of impedances can be best explained by the 'electrochemical cleaning' theory associated with the first stimulation of the electrode. However, for both impedances and tNRTs there also is an important impact of time as well as of acute perioperative changes in electrical conductivity.
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Affiliation(s)
- F Christov
- a Department of Otolaryngology, Head and Neck Surgery , University Hospital Essen , Essen , Germany.,b Section of Otolaryngology-Head & Neck Surgery , University of Chicago Medicine , Illinois , USA
| | - M B Gluth
- b Section of Otolaryngology-Head & Neck Surgery , University of Chicago Medicine , Illinois , USA
| | - S J Lahti
- c Department of Medicine , Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - S Ludwig
- a Department of Otolaryngology, Head and Neck Surgery , University Hospital Essen , Essen , Germany
| | - S Hans
- a Department of Otolaryngology, Head and Neck Surgery , University Hospital Essen , Essen , Germany
| | - L C Holtmann
- a Department of Otolaryngology, Head and Neck Surgery , University Hospital Essen , Essen , Germany
| | - S Lang
- a Department of Otolaryngology, Head and Neck Surgery , University Hospital Essen , Essen , Germany
| | - D Arweiler-Harbeck
- a Department of Otolaryngology, Head and Neck Surgery , University Hospital Essen , Essen , Germany
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Charaziak KK, Shera CA, Siegel JH. Using Cochlear Microphonic Potentials to Localize Peripheral Hearing Loss. Front Neurosci 2017; 11:169. [PMID: 28420953 PMCID: PMC5378797 DOI: 10.3389/fnins.2017.00169] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 03/14/2017] [Indexed: 11/13/2022] Open
Abstract
The cochlear microphonic (CM) is created primarily by the receptor currents of outer hair cells (OHCs) and may therefore be useful for identifying cochlear regions with impaired OHCs. However, the CM measured across the frequency range with round-window or ear-canal electrodes lacks place-specificity as it is dominated by cellular sources located most proximal to the recording site (e.g., at the cochlear base). To overcome this limitation, we extract the "residual" CM (rCM), defined as the complex difference between the CM measured with and without an additional tone (saturating tone, ST). If the ST saturates receptor currents near the peak of its excitation pattern, then the rCM should reflect the activity of OHCs in that region. To test this idea, we measured round-window CMs in chinchillas in response to low-level probe tones presented alone or with an ST ranging from 1 to 2.6 times the probe frequency. CMs were measured both before and after inducing a local impairment in cochlear function (a 4-kHz notch-type acoustic trauma). Following the acoustic trauma, little change was observed in the probe-alone CM. In contrast, rCMs were reduced in a frequency-specific manner. When shifts in rCM levels were plotted vs. the ST frequency, they matched well the frequency range of shifts in neural thresholds. These results suggest that rCMs originate near the cochlear place tuned to the ST frequency and thus can be used to assess OHC function in that region. Our interpretation of the data is supported by predictions of a simple phenomenological model of CM generation and two-tone interactions. The model indicates that the sensitivity of rCM to acoustic trauma is governed by changes in cochlear response at the ST tonotopic place rather than at the probe place. The model also suggests that a combination of CM and rCM measurements could be used to assess both the site and etiology of sensory hearing loss in clinical applications.
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Affiliation(s)
- Karolina K Charaziak
- Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern CaliforniaLos Angeles, CA, USA.,Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Hugh Knowles Center, Northwestern UniversityEvanston, IL, USA
| | - Christopher A Shera
- Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern CaliforniaLos Angeles, CA, USA
| | - Jonathan H Siegel
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Hugh Knowles Center, Northwestern UniversityEvanston, IL, USA
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