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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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Guérit F, Middlebrooks JC, Gransier R, Richardson ML, Wouters J, Carlyon RP. Exploring the Use of Interleaved Stimuli to Measure Cochlear-Implant Excitation Patterns. J Assoc Res Otolaryngol 2024; 25:201-213. [PMID: 38459245 PMCID: PMC11018570 DOI: 10.1007/s10162-024-00937-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 02/15/2024] [Indexed: 03/10/2024] Open
Abstract
PURPOSE Attempts to use current-focussing strategies with cochlear implants (CI) to reduce neural spread-of-excitation have met with only mixed success in human studies, in contrast to promising results in animal studies. Although this discrepancy could stem from between-species anatomical and aetiological differences, the masking experiments used in human studies may be insufficiently sensitive to differences in excitation-pattern width. METHODS We used an interleaved-masking method to measure psychophysical excitation patterns in seven participants with four masker stimulation configurations: monopolar (MP), partial tripolar (pTP), a wider partial tripolar (pTP + 2), and, importantly, a condition (RP + 2) designed to produce a broader excitation pattern than MP. The probe was always in partial-tripolar configuration. RESULTS We found a significant effect of stimulation configuration on both the amount of on-site masking (mask and probe on same electrode; an indirect indicator of sharpness) and the difference between off-site and on-site masking. Differences were driven solely by RP + 2 producing a broader excitation pattern than the other configurations, whereas monopolar and the two current-focussing configurations did not statistically differ from each other. CONCLUSION A method that is sensitive enough to reveal a modest broadening in RP + 2 showed no evidence for sharpening with focussed stimulation. We also showed that although voltage recordings from the implant accurately predicted a broadening of the psychophysical excitation patterns with RP + 2, they wrongly predicted a strong sharpening with pTP + 2. We additionally argue, based on our recent research, that the interleaved-masking method can usefully be applied to non-human species and objective measures of CI excitation patterns.
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Affiliation(s)
- François Guérit
- Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, England.
| | - John C Middlebrooks
- Department of Otolaryngology, University of California at Irvine, Irvine, CA, USA
- Department of Neurobiology and Behavior, University of California at Irvine, Irvine, CA, USA
- Department of Biomedical Engineering, University of California at Irvine, Irvine, CA, USA
| | - Robin Gransier
- Department of Neurosciences, ExpORL KU Leuven, Leuven, Belgium
- Leuven Brain Institute KU Leuven, Leuven, Belgium
| | - Matthew L Richardson
- Department of Otolaryngology, University of California at Irvine, Irvine, CA, USA
| | - Jan Wouters
- Department of Neurosciences, ExpORL KU Leuven, Leuven, Belgium
- Leuven Brain Institute KU Leuven, Leuven, Belgium
| | - Robert P Carlyon
- Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, England
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van Groesen NRA, Briaire JJ, de Jong MAM, Frijns JHM. Dynamic Current Focusing Compared to Monopolar Stimulation in a Take-Home Trial of Cochlear Implant Users. Ear Hear 2023; 44:306-317. [PMID: 36279119 DOI: 10.1097/aud.0000000000001282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
OBJECTIVES This study compared the performance of a dynamic partial tripolar cochlear implant speech encoding strategy termed dynamic current focusing (DCF) to monopolar stimulation (MP) using spectro-temporal, temporal, and speech-in-noise recognition testing. DESIGN DCF is a strategy that utilizes tripolar or high partial tripolar stimulation at threshold level and increases loudness by slowly widening current spread towards most comfortable level. Thirteen cochlear implant users were fitted with DCF and a non-steered MP matched on pulse rate, pulse width, and active electrodes. Nine participants completed the single-blinded within-subject crossover trial. Repeated testing consisted of four sessions. Strategies were allocated in a DCF-MP-DCF-MP or MP-DCF-MP-DCF design. Three-week adaptation periods ended with a test session in which speech-in-noise recognition (matrix speech-in-noise sentence test), spectro-temporal ripple tests (SMRT and STRIPES) and a temporal amplitude modulation detection test were conducted. All participants recorded their subjective experiences with both strategies using the Speech, Spatial and Qualities of Hearing Scale questionnaire. RESULTS Participants' SMRT thresholds improved 0.40 ripples per octave ( p = 0.02, Bonferroni-corrected: p = 0.1) with DCF over MP at 65 dB SPL. No significant differences between the strategies were found on speech-in-noise recognition at conversational (65 dB SPL) and soft (45 dB SPL) loudness levels, temporal testing, STRIPES, or the SMRT at 45 dB SPL. After Bonferroni correction, a learning effect remained on the matrix speech-in-noise sentence test at both loudness levels (65 dB SPL: p = 0.01; 45 dB SPL: p = 0.02). There was no difference in learning effects over time between DCF and MP. Similarly, no significant differences were found in subjective experience on the Speech, Spatial and Qualities of Hearing Scale questionnaire. DCF reduced average battery life by 48% (5.1 hours) ( p < 0.001) compared to MP. CONCLUSIONS DCF may improve spectral resolution over MP at comfortable loudness (65 dB SPL) in cochlear implant users. However, the evidence collected in this study was weak and the significant result disappeared after Bonferroni correction. Also, not all spectral tests revealed this improvement. As expected, battery life was reduced for DCF. Although the current study is limited by its small sample size, considering previous studies, DCF does not consistently improve speech recognition in noise over MP strategies.
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Affiliation(s)
| | - Jeroen Johannes Briaire
- Otorhinolaryngology and Head and Neck Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Monique Anna Maria de Jong
- Otorhinolaryngology and Head and Neck Surgery, Leiden University Medical Center, Leiden, the Netherlands
| | - Johannes Hubertus Maria Frijns
- Otorhinolaryngology and Head and Neck Surgery, Leiden University Medical Center, Leiden, the Netherlands
- Leiden Institute for Brain and Cognition, Leiden, the Netherlands
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van Gendt MJ, Siebrecht M, Briaire JJ, Bohte SM, Frijns JHM. Short and long-term adaptation in the auditory nerve stimulated with high-rate electrical pulse trains are better described by a power law. Hear Res 2020; 398:108090. [PMID: 33070033 DOI: 10.1016/j.heares.2020.108090] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 09/02/2020] [Accepted: 09/22/2020] [Indexed: 01/18/2023]
Abstract
Despite the introduction of many new sound-coding strategies speech perception outcomes in cochlear implant listeners have leveled off. Computer models may help speed up the evaluation of new sound-coding strategies, but most existing models of auditory nerve responses to electrical stimulation include limited temporal detail, as the effects of longer stimulation, such as adaptation, are not well-studied. Measured neural responses to stimulation with both short (400 ms) and long (10 min) duration high-rate (5kpps) pulse trains were compared in terms of spike rate and vector strength (VS) with model outcomes obtained with different forms of adaptation. A previously published model combining biophysical and phenomenological approaches was adjusted with adaptation modeled as a single decaying exponent, multiple exponents and a power law. For long duration data, power law adaptation by far outperforms the single exponent model, especially when it is optimized per fiber. For short duration data, all tested models performed comparably well, with slightly better performance of the single exponent model for VS and of the power law model for the spike rates. The power law parameter sets obtained when fitted to the long duration data also yielded adequate predictions for short duration stimulation, and vice versa. The power law function can be approximated with multiple exponents, which is physiologically more viable. The number of required exponents depends on the duration of simulation; the 400 ms data was well-replicated by two exponents (23 and 212 ms), whereas the 10-minute data required at least seven exponents (ranging from 4 ms to 600 s). Adaptation of the auditory nerve to high-rate electrical stimulation can best be described by a power-law or a sum of exponents. This gives an adequate fit for both short and long duration stimuli, such as CI speech segments.
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Affiliation(s)
- M J van Gendt
- ENT-Department, Leiden University Medical Centre, PO Box 9600, Leiden 2300 RC, The Netherlands.
| | - M Siebrecht
- ENT-Department, Leiden University Medical Centre, PO Box 9600, Leiden 2300 RC, The Netherlands
| | - J J Briaire
- ENT-Department, Leiden University Medical Centre, PO Box 9600, Leiden 2300 RC, The Netherlands
| | - S M Bohte
- CWI, Center for Mathematics and Informatics, Amsterdam, The Netherlands
| | - J H M Frijns
- ENT-Department, Leiden University Medical Centre, PO Box 9600, Leiden 2300 RC, The Netherlands
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Dombrowski T, Rankovic V, Moser T. Toward the Optical Cochlear Implant. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033225. [PMID: 30323016 DOI: 10.1101/cshperspect.a033225] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
When hearing fails, cochlear implants (CIs) provide open speech perception to most of the currently half a million CI users. CIs bypass the defective sensory organ and stimulate the auditory nerve electrically. The major bottleneck of current CIs is the poor coding of spectral information, which results from wide current spread from each electrode contact. As light can be more conveniently confined, optical stimulation of the auditory nerve presents a promising perspective for a fundamental advance of CIs. Moreover, given the improved frequency resolution of optical excitation and its versatility for arbitrary stimulation patterns the approach also bears potential for auditory research. Here, we review the current state of the art focusing on the emerging concept of optogenetic stimulation of the auditory pathway. Developing optogenetic stimulation for auditory research and future CIs requires efforts toward viral gene transfer to the neurons, design and characterization of appropriate optogenetic actuators, as well as engineering of multichannel optical implants.
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Affiliation(s)
- Tobias Dombrowski
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center, 37075 Göttingen, Germany.,Department of Otorhinolaryngology, Head and Neck Surgery, Ruhr University Bochum, St. Elisabeth Hospital, 44787 Bochum, Germany
| | - Vladan Rankovic
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center, 37075 Göttingen, Germany.,Auditory Neuroscience and Optogenetics Group, German Primate Center, 37077 Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center, 37075 Göttingen, Germany.,Auditory Neuroscience and Optogenetics Group, German Primate Center, 37077 Göttingen, Germany.,Auditory Neuroscience Group, Max-Planck-Institute for Experimental Medicine, 37075 Göttingen, Germany
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de Jong MAM, Briaire JJ, van der Woude SFS, Frijns JHM. Dynamic current focusing for loudness encoding in cochlear implants: a take-home trial. Int J Audiol 2019; 58:553-564. [PMID: 31012768 DOI: 10.1080/14992027.2019.1601270] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Objective: This study aimed to evaluate a more energy-efficient dynamic current focussing (DCF) speech-processing strategy after long-term listening experience. In DCF, tripolar stimulation is used near the threshold and loudness is controlled by the compensation coefficient σ. A recent acute pilot study showed improved spectral-temporally modulated ripple test (SMRT) scores at low loudness levels, but battery life was reduced to 1.5-4 hours. Design: Within-subject comparisons were made for the clinical versus. DCF strategy after 5 weeks of at-home usage. Speech intelligibility in noise, spectral ripple discrimination, temporal modulation detection, loudness growth, and subjective ratings were assessed. Study sample: Twenty HiRes90K (Advanced Bionics, Valencia, USA) cochlear implant (CI) users. Results: Average battery life was 9 hours with the newly implemented DCF compared to 13.4 hours with the clinical strategy. Compared with measurements made at the beginning of the study, SMRT-scores and speech intelligibility in noise were significantly improved with DCF. However, both measures suffered from unexpected learning effects over time. The improvement disappeared and speech intelligibility in noise declined significantly relative to the final control measurement with the clinical strategy. Conclusion: Most CI users can adapt to the DCF strategy in a take-home setting. Although DCF has the potential to improve performance on the SMRT test, learning effects complicate the interpretation of the current results.
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Affiliation(s)
- Monique A M de Jong
- a Department of Otorhinolaryngology and Head and Neck Surgery , Leiden University Medical Center , Leiden , the Netherlands
| | - Jeroen J Briaire
- a Department of Otorhinolaryngology and Head and Neck Surgery , Leiden University Medical Center , Leiden , the Netherlands
| | - Séline F S van der Woude
- a Department of Otorhinolaryngology and Head and Neck Surgery , Leiden University Medical Center , Leiden , the Netherlands
| | - Johan H M Frijns
- a Department of Otorhinolaryngology and Head and Neck Surgery , Leiden University Medical Center , Leiden , the Netherlands.,b Leiden Institute for Brain and Cognition, Leiden University , Leiden , the Netherlands
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Abstract
OBJECTIVES In an attempt to improve spectral resolution and speech intelligibility, several current focusing methods have been proposed to increase spatial selectivity by decreasing intracochlear current spread. For example, tripolar stimulation administers current to a central electrode and uses the two flanking electrodes as the return pathway, creating a narrower intracochlear electrical field and hence increases spectral resolution when compared with monopolar (MP) stimulation. However, more current is required, and in some patients, specifically the ones with high electrode impedances, full loudness growth cannot be supported because of compliance limits. The present study describes and analyses a new loudness encoding approach that uses tripolar stimulation near threshold and gradually broadens the excitation (by decreasing compensation coefficient σ) to increase loudness without the need to increase overall current. It is hypothesized that this dynamic current focusing (DCF) strategy increases spatial selectivity, especially at lower loudness levels, while maintaining maximum selectivity at higher loudness levels, without reaching compliance limits. DESIGN Eleven adult cochlear implant recipients with postlingual hearing loss, with at least 9 months of experience with their HiRes90K implant, were selected to participate in this study. Baseline performance regarding speech intelligibility in noise (Dutch matrix sentence test), spectral ripple discrimination at 45 and 65 dB, and temporal modulation detection thresholds were assessed using their own clinical program, fitted on a Harmony processor. Subsequently, the DCF strategy was fitted on a research Harmony processor. Threshold levels were determined with σ = 0.8, which means 80% of current is returned to the flanking electrodes and the remaining 20% to the extracochlear ground electrode. Instead of increasing overall pulse magnitude, σ was decreased to determine most comfortable loudness. After 2 to 3 hr of adaptation to the research strategy, the same psychophysical measures were taken. RESULTS At 45 dB, average spectral ripple scores improved significantly from 2.4 ripples per octave with their clinical program to 3.74 ripples per octave with the DCF strategy (p = 0.016). Eight out of 11 participants had an improved spectral resolution at 65 dB. Nevertheless, no significant difference between DCF and MP was observed at higher presentation levels. Both speech-in-noise and temporal modulation detection thresholds were equal for MP and DCF strategies. Subjectively, 2 participants preferred the DCF strategy over their own clinical program, 2 preferred their own strategy, while the majority of the participants had no preference. Battery life was decreased and ranged from 1.5 to 4 hr. CONCLUSIONS The DCF strategy gives better spectral resolution, at lower loudness levels, but equal performance on speech tests. These outcomes warrant for a longer adaptation period to study long-term outcomes and evaluate if the outcomes in the ripple tests transfer to the speech scores. Further research, for example, with respect to fitting rules and reduction of power consumption, is necessary to make the DCF strategy suitable for routine clinical application.
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Reducing interaction in simultaneous paired stimulation with CI. PLoS One 2017; 12:e0171071. [PMID: 28182685 PMCID: PMC5300223 DOI: 10.1371/journal.pone.0171071] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Accepted: 01/17/2017] [Indexed: 12/05/2022] Open
Abstract
In this study simultaneous paired stimulation of electrodes in cochlear implants is investigated by psychophysical experiments in 8 post-lingually deaf subjects (and one extra subject who only participated in part of the experiments). Simultaneous and sequential monopolar stimulation modes are used as references and are compared to channel interaction compensation, partial tripolar stimulation and a novel sequential stimulation strategy named phased array compensation. Psychophysical experiments are performed to investigate both the loudness integration during paired stimulation at the main electrodes as well as the interaction with the electrode contact located halfway between the stimulating pair. The study shows that simultaneous monopolar stimulation has more loudness integration on the main electrodes and more interaction in between the electrodes than sequential stimulation. Channel interaction compensation works to reduce the loudness integration at the main electrodes, but does not reduce the interaction in between the electrodes caused by paired stimulation. Partial tripolar stimulation uses much more current to reach the needed loudness, but shows the same interaction in between the electrodes as sequential monopolar stimulation. In phased array compensation we have used the individual impedance matrix of each subject to calculate the current needed on each electrode to exactly match the stimulation voltage along the array to that of sequential stimulation. The results show that the interaction in between the electrodes is the same as monopolar stimulation. The strategy uses less current than partial tripolar stimulation, but more than monopolar stimulation. In conclusion, the paper shows that paired stimulation is possible if the interaction is compensated.
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