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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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Quass GL, Kral A. Tripolar configuration and pulse shape in cochlear implants reduce channel interactions in the temporal domain. Hear Res 2024; 443:108953. [PMID: 38277881 DOI: 10.1016/j.heares.2024.108953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Revised: 01/08/2024] [Accepted: 01/11/2024] [Indexed: 01/28/2024]
Abstract
The present study investigates effects of current focusing and pulse shape on threshold, dynamic range, spread of excitation and channel interaction in the time domain using cochlear implant stimulation. The study was performed on 20 adult guinea pigs using a 6-channel animal cochlear implant, recording was performed in the auditory midbrain using a multielectrode array. After determining the best frequencies for individual recording contacts with acoustic stimulation, the ear was deafened and a cochlear implant was inserted into the cochlea. The position of the implant was controlled by x-ray. Stimulation with biphasic, pseudomonophasic and monophasic stimuli was performed with monopolar, monopolar with common ground, bipolar and tripolar configuration in two sets of experiments, allowing comparison of the effects of the different stimulation strategies on threshold, dynamic range, spread of excitation and channel interaction. Channel interaction was studied in the temporal domain, where two electrodes were activated with pulse trains and phase locking to these pulse trains in the midbrain was quantified. The results documented multifactorial influences on the response properties, with significant interaction between factors. Thresholds increased with increasing current focusing, but decreased with pseudomonophasic and monophasic pulse shapes. The results documented that current focusing, particularly tripolar configuration, effectively reduces channel interaction, but that also pseudomonophasic and monophasic stimulation and phase duration intensity coding reduce channel interactions.
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Affiliation(s)
- Gunnar L Quass
- Institute for AudioNeuroTechnology (VIANNA) & Department of Experimental Otology, Otolaryngology Clinics, Hannover Medical School, Hannover, Germany; Cluster of Excellence "Hearing4All" (EXC 2177), Germany.
| | - Andrej Kral
- Institute for AudioNeuroTechnology (VIANNA) & Department of Experimental Otology, Otolaryngology Clinics, Hannover Medical School, Hannover, Germany; Cluster of Excellence "Hearing4All" (EXC 2177), Germany; Australian Hearing Hub, School of Medicine and Health Sciences, Macquarie University, Sydney, Australia
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3
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Joly CA, Reynard P, Hermann R, Seldran F, Gallego S, Idriss S, Thai-Van H. Intra-Cochlear Current Spread Correlates with Speech Perception in Experienced Adult Cochlear Implant Users. J Clin Med 2021; 10:jcm10245819. [PMID: 34945115 PMCID: PMC8709369 DOI: 10.3390/jcm10245819] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/03/2021] [Accepted: 12/08/2021] [Indexed: 11/16/2022] Open
Abstract
Broader intra-cochlear current spread (ICCS) implies higher cochlear implant (CI) channel interactions. This study aimed to investigate the relationship between ICCS and speech intelligibility in experienced CI users. Using voltage matrices collected for impedance measurements, an individual exponential spread coefficient (ESC) was computed. Speech audiometry was performed to determine the intelligibility at 40 dB Sound Pressure Level (SPL) and the 50% speech reception threshold: I40 and SRT50 respectively. Correlations between ESC and either I40 or SRT50 were assessed. A total of 36 adults (mean age: 50 years) with more than 11 months (mean: 34 months) of CI experience were included. In the 21 subjects for whom all electrodes were active, ESC was moderately correlated with both I40 (r = −0.557, p = 0.009) and SRT50 (r = 0.569, p = 0.007). The results indicate that speech perception performance is negatively affected by the ICCS. Estimates of current spread at the closest vicinity of CI electrodes and prior to any activation of auditory neurons are indispensable to better characterize the relationship between CI stimulation and auditory perception in cochlear implantees.
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Affiliation(s)
- Charles-Alexandre Joly
- Institut de l’Audition, Institut Pasteur, Université de Paris, INSERM, 75012 Paris, France; (C.-A.J.); (P.R.)
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France; (R.H.); (S.G.)
- Service d’Audiologie et d’Explorations Otoneurologiques, Hôpital Edouard Herriot, Hospices Civils de Lyon, 69003 Lyon, France;
| | - Pierre Reynard
- Institut de l’Audition, Institut Pasteur, Université de Paris, INSERM, 75012 Paris, France; (C.-A.J.); (P.R.)
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France; (R.H.); (S.G.)
- Service d’Audiologie et d’Explorations Otoneurologiques, Hôpital Edouard Herriot, Hospices Civils de Lyon, 69003 Lyon, France;
| | - Ruben Hermann
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France; (R.H.); (S.G.)
- Integrative, Multisensory, Perception, Action and Cognition Team (IMPACT), Inserm U1028, CNRS UMR5292, Lyon Neuroscience Research Center, 69675 Bron, France
- Service d’ORL, Chirurgie Cervico-Faciale et d’Audiophonologie, Hospices Civils de Lyon, Hôpital Edouard Herriot, 69003 Lyon, France
| | | | - Stéphane Gallego
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France; (R.H.); (S.G.)
- Neuronal Dynamics and Audition Team (DNA), Laboratory of Cognitive Neuroscience, CNRS UMR7291, Aix-Marseille University, CEDEX 3, 13331 Marseille, France
| | - Samar Idriss
- Service d’Audiologie et d’Explorations Otoneurologiques, Hôpital Edouard Herriot, Hospices Civils de Lyon, 69003 Lyon, France;
| | - Hung Thai-Van
- Institut de l’Audition, Institut Pasteur, Université de Paris, INSERM, 75012 Paris, France; (C.-A.J.); (P.R.)
- Université Claude Bernard Lyon 1, 69100 Villeurbanne, France; (R.H.); (S.G.)
- Service d’Audiologie et d’Explorations Otoneurologiques, Hôpital Edouard Herriot, Hospices Civils de Lyon, 69003 Lyon, France;
- Correspondence:
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Recugnat M, Undurraga JA, McAlpine D. Spike-rate adaptation in a computational model of human-shaped spiral ganglion neurons. IEEE Trans Biomed Eng 2021; 69:602-612. [PMID: 34347592 DOI: 10.1109/tbme.2021.3102129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
OBJECTIVES The purpose of this study is to develop a biophysical model of human spiral ganglion neurons (SGNs) that includes voltage-gated hyperpolarization-activated cation (HCN) channels and low-threshold potassium voltage-gated, delayed-rectifier low-threshold potassium (KLT) channels, providing for a more complete simulation of spike-rate adaptation, a feature of most spiking neurons in which spiking activity is reduced in response to sustained stimulation. METHODS Our model incorporates features of spike-rate adaptation reported from in vivo studies, whilst also displaying similar behaviour to existing models of human SGNs, including the dependence of electrically evoked thresholds on the polarity of electrical pulses. RESULTS Hypothesizing that the mode of stimulation intracellular or extracellular predicts features of spike-rate adaptation similar to in vivo studies, including the influence of stimulus intensity and pulse-rate, we find that the mode of stimulation alters features of spike-rate adaptation. In particular, the reduction in spiking over time with sustained input was generally greater for extracellular, compared to intracellular, stimulation, when simulating a multi-compartment SGN with human morphological features. In contrast, time-constants of spike-rate adaption reported for in vivo data did not fit our predicted responses, highlighting the need for a more complete physiological understanding of the factors contributing to spike-rate adaptation in electrically stimulated human SGNs. CONCLUSION Our model extends previous computational models of SGNs with human morphology with ionic channels accounting for features of spike-rate adaptation. SIGNIFICANCE The significance of this work resides in the ability to improve the modeling of cochlear implant (CI) stimulation and its effects on neural responses. This will help develop novel, and perhaps personalised, stimulation strategies to reduce variability in CI user outcomes.
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Viral-mediated transduction of auditory neurons with opsins for optical and hybrid activation. Sci Rep 2021; 11:11229. [PMID: 34045604 PMCID: PMC8160204 DOI: 10.1038/s41598-021-90764-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Accepted: 05/13/2021] [Indexed: 12/15/2022] Open
Abstract
Optical stimulation is a paradigm-shifting approach to modulating neural activity that has the potential to overcome the issue of current spread that occurs with electrical stimulation by providing focused stimuli. But optical stimulation either requires high power infrared light or genetic modification of neurons to make them responsive to lower power visible light. This work examines optical activation of auditory neurons following optogenetic modification via AAV injection in two species (mouse and guinea pig). An Anc80 viral vector was used to express the channelrhodopsin variant ChR2-H134R fused to a fluorescent reporter gene under the control of the human synapsin-1 promoter. The AAV was administered directly to the cochlea (n = 33) or posterior semi-circular canal of C57BL/6 mice (n = 4) or to guinea pig cochleae (n = 6). Light (488 nm), electrical stimuli or the combination of these (hybrid stimulation) was delivered to the cochlea via a laser-coupled optical fibre and co-located platinum wire. Activation thresholds, spread of activation and stimulus interactions were obtained from multi-unit recordings from the central nucleus of the inferior colliculus of injected mice, as well as ChR2-H134R transgenic mice (n = 4). Expression of ChR2-H134R was examined by histology. In the mouse, transduction of auditory neurons by the Anc80 viral vector was most successful when injected at a neonatal age with up to 89% of neurons transduced. Auditory neuron transductions were not successful in guinea pigs. Inferior colliculus responses to optical stimuli were detected in a cochleotopic manner in all mice with ChR2-H134R expression. There was a significant correlation between lower activation thresholds in mice and higher proportions of transduced neurons. There was no difference in spread of activation between optical stimulation and electrical stimulation provided by the light/electrical delivery system used here (optical fibre with bonded 25 µm platinum/iridium wire). Hybrid stimulation, comprised of sub-threshold optical stimulation to 'prime' or raise the excitability of the neurons, lowered the threshold for electrical activation in most cases, but the impact on excitation width was more variable compared to transgenic mice. This study demonstrates the impact of opsin expression levels and expression pattern on optical and hybrid stimulation when considering optical or hybrid stimulation techniques for neuromodulation.
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Guérit F, Marozeau J, Epp B, Carlyon RP. Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users. J Assoc Res Otolaryngol 2020; 21:497-510. [PMID: 32833160 PMCID: PMC7644659 DOI: 10.1007/s10162-020-00767-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 07/31/2020] [Indexed: 12/21/2022] Open
Abstract
The effect of the relative timing between pairs of same-polarity monophasic pulses has been studied extensively in single-neuron animal studies and has revealed fundamental properties of the neurons. For human cochlear implant listeners, the requirement to use charge-balanced stimulation and the typical use of symmetric, biphasic pulses limits such measures, because currents of opposite polarities interact at the level of the neural membrane. Here, we propose a paradigm to study same-polarity summation of currents while keeping the stimulation charge-balanced within a short time window. We used pairs of mirrored pseudo-monophasic pulses (a long-low phase followed by a short-high phase for the first pulse and a short-high phase followed by a long-low phase for the second pulse). We assumed that most of the excitation would stem from the two adjacent short-high phases, which had the same polarity. The inter-pulse interval between the short-high phases was varied from 0 to 345 μs. The inter-pulse interval had a significant effect on the perceived loudness, and this effect was consistent with both passive (membrane-related) and active (ion-channel-related) neuronal mechanisms contributing to facilitation. Furthermore, the effect of interval interacted with the polarity of the pulse pairs. At threshold, there was an effect of polarity, but, surprisingly, no effect of interval nor an interaction between the two factors. We discuss possible peripheral origins of these results.
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Affiliation(s)
- François Guérit
- Hearing Systems Group, Department of Health Technology, Technical University of Denmark, 352 Ørsteds Plads, 2800, Kgs. Lyngby, Denmark.
- Cambridge Hearing Group, MRC Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom.
| | - Jeremy Marozeau
- Hearing Systems Group, Department of Health Technology, Technical University of Denmark, 352 Ørsteds Plads, 2800, Kgs. Lyngby, Denmark
| | - Bastian Epp
- Hearing Systems Group, Department of Health Technology, Technical University of Denmark, 352 Ørsteds Plads, 2800, Kgs. Lyngby, Denmark
| | - Robert P Carlyon
- Cambridge Hearing Group, MRC Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom
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Thompson AC, Wise AK, Hart WL, Needham K, Fallon JB, Gunewardene N, Stoddart PR, Richardson RT. Hybrid optogenetic and electrical stimulation for greater spatial resolution and temporal fidelity of cochlear activation. J Neural Eng 2020; 17:056046. [PMID: 33036009 DOI: 10.1088/1741-2552/abbff0] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Compared to electrical stimulation, optogenetic stimulation has the potential to improve the spatial precision of neural activation in neuroprostheses, but it requires intense light and has relatively poor temporal kinetics. We tested the effect of hybrid stimulation, which is the combination of subthreshold optical and electrical stimuli, on spectral and temporal fidelity in the cochlea by recording multiunit activity in the inferior colliculus of channelrhodopsin (H134R variant) transgenic mice. APPROACH Pulsed light or biphasic electrical pulses were delivered to cochlear spiral ganglion neurons of acutely deafened mice, either as individual stimuli or as hybrid stimuli for which the timing of the electrical pulse had a varied delay relative to the start of the optical pulse. Response thresholds, spread of activation and entrainment data were obtained from multi-unit recordings from the auditory midbrain. MAIN RESULTS Facilitation occurred when subthreshold electrical stimuli were applied at the end of, or up to 3.75 ms after subthreshold optical pulses. The spread of activation resulting from hybrid stimulation was significantly narrower than electrical-only and optical-only stimulation (p < 0.01), measured at equivalent suprathreshold levels of loudness that are relevant to cochlear implant users. Furthermore, temporal fidelity, measured as maximum following rates to 300 ms pulse trains bursts up to 240 Hz, was 2.4-fold greater than optical-only stimulation (p < 0.05). SIGNIFICANCE By significantly improving spectral resolution of electrical- and optical-only stimulation and the temporal fidelity of optical-only stimulation, hybrid stimulation has the potential to increase the number of perceptually independent stimulating channels in a cochlear implant.
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Lamping W, Goehring T, Marozeau J, Carlyon RP. The effect of a coding strategy that removes temporally masked pulses on speech perception by cochlear implant users. Hear Res 2020; 391:107969. [PMID: 32320925 PMCID: PMC7116331 DOI: 10.1016/j.heares.2020.107969] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 03/26/2020] [Accepted: 04/05/2020] [Indexed: 01/11/2023]
Abstract
Speech recognition in noisy environments remains a challenge for cochlear implant (CI) recipients. Unwanted charge interactions between current pulses, both within and between electrode channels, are likely to impair performance. Here we investigate the effect of reducing the number of current pulses on speech perception. This was achieved by implementing a psychoacoustic temporal-masking model where current pulses in each channel were passed through a temporal integrator to identify and remove pulses that were less likely to be perceived by the recipient. The decision criterion of the temporal integrator was varied to control the percentage of pulses removed in each condition. In experiment 1, speech in quiet was processed with a standard Continuous Interleaved Sampling (CIS) strategy and with 25, 50 and 75% of pulses removed. In experiment 2, performance was measured for speech in noise with the CIS reference and with 50 and 75% of pulses removed. Speech intelligibility in quiet revealed no significant difference between reference and test conditions. For speech in noise, results showed a significant improvement of 2.4 dB when removing 50% of pulses and performance was not significantly different between the reference and when 75% of pulses were removed. Further, by reducing the overall amount of current pulses by 25, 50, and 75% but accounting for the increase in charge necessary to compensate for the decrease in loudness, estimated average power savings of 21.15, 40.95, and 63.45%, respectively, could be possible for this set of listeners. In conclusion, removing temporally masked pulses may improve speech perception in noise and result in substantial power savings.
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Affiliation(s)
- Wiebke Lamping
- Hearing Systems Section, Department of Health Technology, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark; Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom.
| | - Tobias Goehring
- Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom
| | - Jeremy Marozeau
- Hearing Systems Section, Department of Health Technology, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark
| | - Robert P Carlyon
- Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom
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George SS, Shivdasani MN, Fallon JB. Effect of current focusing on the sensitivity of inferior colliculus neurons to amplitude-modulated stimulation. J Neurophysiol 2016; 116:1104-16. [PMID: 27306672 DOI: 10.1152/jn.00126.2016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Accepted: 06/15/2016] [Indexed: 11/22/2022] Open
Abstract
In multichannel cochlear implants (CIs), current is delivered to specific electrodes along the cochlea in the form of amplitude-modulated pulse trains, to convey temporal and spectral cues. Our previous studies have shown that focused multipolar (FMP) and tripolar (TP) stimulation produce more restricted neural activation and reduced channel interactions in the inferior colliculus (IC) compared with traditional monopolar (MP) stimulation, suggesting that focusing of stimulation could produce better transmission of spectral information. The present study explored the capability of IC neurons to detect modulated CI stimulation with FMP and TP stimulation compared with MP stimulation. The study examined multiunit responses of IC neurons in acutely deafened guinea pigs by systematically varying the stimulation configuration, modulation depth, and stimulation level. Stimuli were sinusoidal amplitude-modulated pulse trains (carrier rate of 120 pulses/s). Modulation sensitivity was quantified by measuring modulation detection thresholds (MDTs), defined as the lowest modulation depth required to differentiate the response of a modulated stimulus from an unmodulated one. Whereas MP stimulation showed significantly lower MDTs than FMP and TP stimulation (P values <0.05) at stimulation ≤2 dB above threshold, all stimulation configurations were found to have similar modulation sensitivities at 4 dB above threshold. There was no difference found in modulation sensitivity between FMP and TP stimulation. The present study demonstrates that current focusing techniques such as FMP and TP can adequately convey amplitude modulation and are comparable to MP stimulation, especially at higher stimulation levels, although there may be some trade-off between spectral and temporal fidelity with current focusing stimulation.
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Affiliation(s)
- Shefin S George
- The Bionics Institute, East Melbourne, Australia; and Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - Mohit N Shivdasani
- The Bionics Institute, East Melbourne, Australia; and Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - James B Fallon
- The Bionics Institute, East Melbourne, Australia; and Department of Medical Bionics, University of Melbourne, Melbourne, Australia
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Guevara N, Hoen M, Truy E, Gallego S. A Cochlear Implant Performance Prognostic Test Based on Electrical Field Interactions Evaluated by eABR (Electrical Auditory Brainstem Responses). PLoS One 2016; 11:e0155008. [PMID: 27149268 PMCID: PMC4858145 DOI: 10.1371/journal.pone.0155008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 04/22/2016] [Indexed: 11/18/2022] Open
Abstract
Background Cochlear implants (CIs) are neural prostheses that have been used routinely in the clinic over the past 25 years. They allow children who were born profoundly deaf, as well as adults affected by hearing loss for whom conventional hearing aids are insufficient, to attain a functional level of hearing. The “modern” CI (i.e., a multi-electrode implant using sequential coding strategies) has yielded good speech comprehension outcomes (recognition level for monosyllabic words about 50% to 60%, and sentence comprehension close to 90%). These good average results however hide a very important interindividual variability as scores in a given patients’ population often vary from 5 to 95% in comparable testing conditions. Our aim was to develop a prognostic model for patients with unilateral CI. A novel method of objectively measuring electrical and neuronal interactions using electrical auditory brainstem responses (eABRs) is proposed. Methods and Findings The method consists of two measurements: 1) eABR measurements with stimulation by a single electrode at 70% of the dynamic range (four electrodes distributed within the cochlea were tested), followed by a summation of these four eABRs; 2) Measurement of a single eABR with stimulation from all four electrodes at 70% of the dynamic range. A comparison of the eABRs obtained by these two measurements, defined as the monaural interaction component (MIC), indicated electrical and neural interactions between the stimulation channels. Speech recognition performance without lip reading was measured for each patient using a logatome test (64 "vowel-consonant-vowel"; VCV; by forced choice of 1 out of 16). eABRs were measured in 16 CI patients (CIs with 20 electrodes, Digisonic SP; Oticon Medical ®, Vallauris, France). Significant correlations were found between speech recognition performance and the ratio of the amplitude of the V wave of the eABRs obtained with the two measurements (Pearson's linear regression model, parametric correlation: r2 = 0.26, p<0.05). Conclusions This prognostic model allowed a substantial amount of the interindividual variance in speech recognition scores to be explained. The present study used measurements of electrical and neuronal interactions by eABR to assess patients' bio-electric capacity to use multiple information channels supplied by the implant. This type of prognostic information may be valuable in several ways. On the patient level, it allows customizing of individual treatments. ClinicalTrials.gov Identifier: NCT01805167
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Affiliation(s)
- Nicolas Guevara
- University Head and Neck Institute, CHU de Nice, 31 Avenue de Valombrose, 06107 Nice cedex 2, France
| | - Michel Hoen
- Oticon Medical, Clinical and Scientific Research Department, 2720 chemin St Bernard, 06220 Vallauris, France
| | - Eric Truy
- Department of Audiology and Otorhinolaryngology, Edouard Herriot Hospital, 5 Place d'Arsonval, 69437 Lyon, France
| | - Stéphane Gallego
- Institute for Readaptation Sciences and Techniques, 8 Avenue Rockefeller, 69373 Lyon Cedex 08, France
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Fielden CA, Kluk K, Boyle PJ, McKay CM. The perception of complex pitch in cochlear implants: A comparison of monopolar and tripolar stimulation. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2015; 138:2524-36. [PMID: 26520335 DOI: 10.1121/1.4931910] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Cochlear implant listeners typically perform poorly in tasks of complex pitch perception (e.g., musical pitch and voice pitch). One explanation is that wide current spread during implant activation creates channel interactions that may interfere with perception of temporal fundamental frequency information contained in the amplitude modulations within channels. Current focusing using a tripolar mode of stimulation has been proposed as a way of reducing channel interactions, minimising spread of excitation and potentially improving place and temporal pitch cues. The present study evaluated the effect of mode in a group of cochlear implant listeners on a pitch ranking task using male and female singing voices separated by either a half or a quarter octave. Results were variable across participants, but on average, pitch ranking was at chance level when the pitches were a quarter octave apart and improved when the difference was a half octave. No advantage was observed for tripolar over monopolar mode at either pitch interval, suggesting that previously published psychophysical advantages for focused modes may not translate into improvements in complex pitch ranking. Evaluation of the spectral centroid of the stimulation pattern, plus a lack of significant difference between male and female voices, suggested that participants may have had difficulty in accessing temporal pitch cues in either mode.
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Affiliation(s)
- Claire A Fielden
- School of Psychological Sciences, University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Karolina Kluk
- School of Psychological Sciences, University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Patrick J Boyle
- Advanced Bionics UK Ltd., 2 Breaks House, Mill Court, Great Shelford, Cambridge, CB22 5LD, United Kingdom
| | - Colette M McKay
- School of Psychological Sciences, University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester M13 9PL, United Kingdom
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Cosentino S, Deeks JM, Carlyon RP. Procedural Factors That Affect Psychophysical Measures of Spatial Selectivity in Cochlear Implant Users. Trends Hear 2015; 19:19/0/2331216515607067. [PMID: 26420785 PMCID: PMC4593626 DOI: 10.1177/2331216515607067] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Behavioral measures of spatial selectivity in cochlear implants are important both for guiding the programing of individual users’ implants and for the evaluation of different stimulation methods. However, the methods used are subject to a number of confounding factors that can contaminate estimates of spatial selectivity. These factors include off-site listening, charge interactions between masker and probe pulses in interleaved masking paradigms, and confusion effects in forward masking. We review the effects of these confounds and discuss methods for minimizing them. We describe one such method in which the level of a 125-pps masker is adjusted so as to mask a 125-pps probe, and where the masker and probe pulses are temporally interleaved. Five experiments describe the method and evaluate the potential roles of the different potential confounding factors. No evidence was obtained for off-site listening of the type observed in acoustic hearing. The choice of the masking paradigm was shown to alter the measured spatial selectivity. For short gaps between masker and probe pulses, both facilitation and refractory mechanisms had an effect on masking; this finding should inform the choice of stimulation rate in interleaved masking experiments. No evidence for confusion effects in forward masking was revealed. It is concluded that the proposed method avoids many potential confounds but that the choice of method should depend on the research question under investigation.
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Affiliation(s)
| | - John M Deeks
- MRC Cognition and Brain Sciences Unit, Cambridge, UK
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George SS, Shivdasani MN, Wise AK, Shepherd RK, Fallon JB. Electrophysiological channel interactions using focused multipolar stimulation for cochlear implants. J Neural Eng 2015; 12:066005. [DOI: 10.1088/1741-2560/12/6/066005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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George SS, Wise AK, Shivdasani MN, Shepherd RK, Fallon JB. Evaluation of focused multipolar stimulation for cochlear implants in acutely deafened cats. J Neural Eng 2015; 11:065003. [PMID: 25420148 DOI: 10.1088/1741-2560/11/6/065003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE The conductive nature of the fluids and tissues of the cochlea can lead to broad activation of spiral ganglion neurons using contemporary cochlear implant stimulation configurations such as monopolar (MP) stimulation. The relatively poor spatial selectivity is thought to limit implant performance, particularly in noisy environments. Several current focusing techniques have been proposed to reduce the spread of activation with the aim towards achieving improved clinical performance. APPROACH The present research evaluated the efficacy of focused multipolar (FMP) stimulation, a relatively new focusing technique in the cochlea, and compared its efficacy to both MP stimulation and tripolar (TP) stimulation. The spread of neural activity across the inferior colliculus (IC), measured by recording the spatial tuning curve, was used as a measure of spatial selectivity. Adult cats (n = 6) were acutely deafened and implanted with an intracochlear electrode array before multi-unit responses were recorded across the cochleotopic gradient of the contralateral IC. Recordings were made in response to acoustic and electrical stimulation using the MP, TP and FMP configurations. MAIN RESULTS FMP and TP stimulation resulted in greater spatial selectivity than MP stimulation. However, thresholds were significantly higher (p < 0.001) for FMP and TP stimulation compared to MP stimulation. There were no differences found in spatial selectivity and threshold between FMP and TP stimulation. SIGNIFICANCE The greater spatial selectivity of FMP and TP stimulation would be expected to result in improved clinical performance. However, further research will be required to demonstrate the efficacy of these modes of stimulation after longer durations of deafness.
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George SS, Wise AK, Fallon JB, Shepherd RK. Evaluation of focused multipolar stimulation for cochlear implants in long-term deafened cats. J Neural Eng 2015; 12:036003. [PMID: 25834113 DOI: 10.1088/1741-2560/12/3/036003] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
OBJECTIVE Focused multipolar (FMP) stimulation has been shown to produce restricted neural activation using intracochlear stimulation in animals with a normal population of spiral ganglion neurons (SGNs). However, in a clinical setting, the widespread loss of SGNs and peripheral fibres following deafness is expected to influence the effectiveness of FMP. APPROACH We compared the efficacy of FMP stimulation to both monopolar (MP) and tripolar (TP) stimulation in long-term deafened cat cochleae (n = 8). Unlike our previous study, these cochleae contained <10% of the normal SGN population adjacent to the electrode array. We also evaluated the effect of electrode position on stimulation modes by using either modiolar facing or lateral wall facing half-band electrodes. The spread of neural activity across the inferior colliculus, a major nucleus within the central auditory pathway, was used as a measure of spatial selectivity. MAIN RESULTS In cochleae with significant SGN degeneration, we observed that FMP and TP stimulation resulted in greater spatial selectivity than MP stimulation (p < 0.001). However, thresholds were significantly higher for FMP and TP stimulation compared to MP stimulation (p < 0.001). No difference between FMP and TP stimulation was found in any measures. The high threshold levels for FMP stimulation was significantly reduced without compromising spatial selectivity by varying the degree of current focusing (referred as 'partial-FMP' stimulation). Spatial selectivity of all stimulation modes was unaffected by the electrode position. Finally, spatial selectivity in long-term deafened cochleae was significantly less than that of cochleae with normal SGN population (George S S et al 2014 J. Neural Eng. 11 065003). SIGNIFICANCE The present results indicate that the greater spatial selectivity of FMP and TP stimulation over MP stimulation is maintained in cochleae with significant neural degeneration and is not adversely affected by electrode position. The greater spatial selectivity of FMP and TP stimulation would be expected to result in improved clinical performance.
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Affiliation(s)
- Shefin S George
- The Bionics Institute, East Melbourne 3002, Australia. Department of Medical Bionics, University of Melbourne, Melbourne 3002, Australia
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Wu CC, Luo X. Electrode spanning with partial tripolar stimulation mode in cochlear implants. J Assoc Res Otolaryngol 2014; 15:1023-36. [PMID: 24865767 DOI: 10.1007/s10162-014-0464-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Accepted: 05/07/2014] [Indexed: 11/26/2022] Open
Abstract
The perceptual effects of electrode spanning (i.e., the use of nonadjacent return electrodes) in partial tripolar (pTP) mode were tested on a main electrode EL8 in five cochlear implant (CI) users. Current focusing was controlled by σ (the ratio of current returned within the cochlea), and current steering was controlled by α (the ratio of current returned to the basal electrode). Experiment 1 tested whether asymmetric spanning with α = 0.5 can create additional channels around standard pTP stimuli. It was found that in general, apical spanning (i.e., returning current to EL6 rather than EL7) elicited a pitch between those of standard pTP stimuli on main electrodes EL8 and EL9, while basal spanning (i.e., returning current to EL10 rather than EL9) elicited a pitch between those of standard pTP stimuli on main electrodes EL7 and EL8. The pitch increase caused by apical spanning was more salient than the pitch decrease caused by basal spanning. To replace the standard pTP channel on the main electrode EL8 when EL7 or EL9 is defective, experiment 2 tested asymmetrically spanned pTP stimuli with various α, and experiment 3 tested symmetrically spanned pTP stimuli with various σ. The results showed that pitch increased with decreasing α in asymmetric spanning, or with increasing σ in symmetric spanning. Apical spanning with α around 0.69 and basal spanning with α around 0.38 may both elicit a similar pitch as the standard pTP stimulus. With the same σ, the symmetrically spanned pTP stimulus was higher in pitch than the standard pTP stimulus. A smaller σ was thus required for symmetric spanning to match the pitch of the standard pTP stimulus. In summary, electrode spanning is an effective field-shaping technique that is useful for adding spectral channels and handling defective electrodes with CIs.
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Affiliation(s)
- Ching-Chih Wu
- School of Electrical and Computer Engineering, Purdue University, 500 Oval Drive, West Lafayette, IN, 47907, USA,
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Quasi-monopolar stimulation: a novel electrode design configuration for performance optimization of a retinal neuroprosthesis. PLoS One 2013; 8:e73130. [PMID: 23991175 PMCID: PMC3753255 DOI: 10.1371/journal.pone.0073130] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2012] [Accepted: 02/21/2013] [Indexed: 11/28/2022] Open
Abstract
In retinal neuroprostheses, spatial interaction between electric fields from various electrodes – electric crosstalk – may occur in multielectrode arrays during simultaneous stimulation of the retina. Depending on the electrode design and placement, this crosstalk can either enhance or degrade the functional characteristics of a visual prosthesis. To optimize the device performance, a balance must be satisfied between the constructive interference of crosstalk on dynamic range and power consumption and its negative effect on artificial visual acuity. In the present computational modeling study, we have examined the trade-off in these positive and negative effects using a range of currently available electrode array configurations, compared to a recently proposed stimulation strategy – the quasi monopolar (QMP) configuration – in which the return current is shared between local bipolar guards and a distant monopolar electrode. We evaluate the performance of the QMP configuration with respect to the implantation site and electrode geometry parameters. Our simulation results demonstrate that the beneficial effects of QMP are only significant at electrode-to-cell distances greater than the electrode dimensions. Possessing a relatively lower activation threshold, QMP was found to be superior to the bipolar configuration in terms of providing a relatively higher visual acuity. However, the threshold for QMP was more sensitive to the topological location of the electrode in the array, which may need to be considered when programming the manner in which electrode are simultaneously activated. This drawback can be offset with a wider dynamic range and lower power consumption of QMP. Furthermore, the ratio of monopolar return current to total return can be used to adjust the functional performance of QMP for a given implantation site and electrode parameters. We conclude that the QMP configuration can be used to improve visual information-to-stimulation mapping in a visual prosthesis, while maintaining low power consumption.
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Bader P, Kals M, Schatzer R, Griessner A, Zierhofer C. Compensation for channel interaction in a simultaneous cochlear implant coding strategy. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2013; 133:4124-4132. [PMID: 23742364 DOI: 10.1121/1.4803848] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This study evaluated a concept to reduce detrimental effects of spatial channel interaction in case of simultaneous stimulation with cochlear implants. The hypothesis was that effects of simultaneous channel interaction can be compensated by an algorithm such that no difference in hearing performance between simultaneous pulsatile stimulation and a strictly sequential reference strategy can be found. The simultaneous strategies used in this study stimulated two or three electrodes simultaneously in a monopolar configuration and used a specific compensation algorithm to reduce detrimental effects of simultaneous channel interaction. Overall stimulation rate was kept constant throughout conditions. Three of the configurations applied extended pulse phase durations. The German Oldenburg sentence and a German vowel test were used to measure speech recognition in 12 cochlear implant users. The results support the initial hypothesis. No significant differences in performance were found. A small spatial distance between simultaneous electrodes yielded slightly better results than a large distance. Extending the pulse phase durations had no significant effect on hearing performance. However, it significantly reduced stimulation amplitudes. Thus strategies implementing channel interaction compensated simultaneous stimulation with extended pulse phase durations might be a viable option for reducing power consumption and increasing battery life in cochlear implants.
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Affiliation(s)
- Paul Bader
- Institute of Mechatronics, Faculty of Engineering Science, University of Innsbruck, Innsbruck, Austria.
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Karg S, Lackner C, Hemmert W. Temporal interaction in electrical hearing elucidates auditory nerve dynamics in humans. Hear Res 2013; 299:10-8. [DOI: 10.1016/j.heares.2013.01.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 01/18/2013] [Accepted: 01/23/2013] [Indexed: 11/24/2022]
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Spelman FA. Cochlear Prostheses. Biomater Sci 2013. [DOI: 10.1016/b978-0-08-087780-8.00083-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Current steering with partial tripolar stimulation mode in cochlear implants. J Assoc Res Otolaryngol 2012; 14:213-31. [PMID: 23250685 DOI: 10.1007/s10162-012-0366-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2012] [Accepted: 12/02/2012] [Indexed: 11/27/2022] Open
Abstract
The large spread of excitation is a major cause of poor spectral resolution for cochlear implant (CI) users. Partial tripolar (pTP) mode has been proposed to reduce current spread by returning an equally distributed fraction (0.5 × σ) of current to two flanking electrodes and the rest to an extra-cochlear ground. This study tested the efficacy of incorporating current steering into pTP mode to add spectral channels. Different proportions of current [α × σ and (1 - α) × σ] were returned to the basal and apical flanking electrodes respectively to shape the electric field. Loudness and pitch perception with α from 0 to 1 in steps of 0.1 was simulated with a computational model of CI stimulation and tested on the apical, middle, and basal electrodes of six CI subjects. The highest σ allowing for full loudness growth within the implant compliance limit was chosen for each main electrode. Pitch ranking was measured between pairs of loudness-balanced steered pTP stimuli with an α interval of 0.1 at the most comfortable level. Results demonstrated that steered pTP stimuli with α around 0.5 required more current to achieve equal loudness than those with α around 0 or 1, maybe due to more focused excitation patterns. Subjects usually perceived decreasing pitches as α increased from 0 to 1, somewhat consistent with the apical shift of the center of gravity of excitation pattern in the model. Pitch discrimination was not better with α around 0.5 than with α around 0 or 1, except for some subjects and electrodes. For three subjects with better pitch discrimination, about half of the pitch ranges of two adjacent main electrodes overlapped with each other in steered pTP mode. These results suggest that current steering with focused pTP mode may improve spectral resolution and pitch perception with CIs.
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Littlefield PD, Vujanovic I, Mundi J, Matic AI, Richter CP. Laser stimulation of single auditory nerve fibers. Laryngoscope 2010; 120:2071-82. [PMID: 20830761 DOI: 10.1002/lary.21102] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECTIVES/HYPOTHESIS One limitation with cochlear implants is the difficulty stimulating spatially discrete spiral ganglion cell groups because of electrode interactions. Multipolar electrodes have improved on this some, but also at the cost of much higher device power consumption. Recently, it has been shown that spatially selective stimulation of the auditory nerve is possible with a mid-infrared laser aimed at the spiral ganglion via the round window. However, these neurons must be driven at adequate rates for optical radiation to be useful in cochlear implants. We herein use single-fiber recordings to characterize the responses of auditory neurons to optical radiation. STUDY DESIGN In vivo study using normal-hearing adult gerbils. METHODS Two diode lasers were used for stimulation of the auditory nerve. They operated between 1.844 μm and 1.873 μm, with pulse durations of 35 μs to 1,000 μs, and at repetition rates up to 1,000 pulses per second (pps). The laser outputs were coupled to a 200-μm-diameter optical fiber placed against the round window membrane and oriented toward the spiral ganglion. The auditory nerve was exposed through a craniotomy, and recordings were taken from single fibers during acoustic and laser stimulation. RESULTS Action potentials occurred 2.5 ms to 4.0 ms after the laser pulse. The latency jitter was up to 3 ms. Maximum rates of discharge averaged 97 ± 52.5 action potentials per second. The neurons did not strictly respond to the laser at stimulation rates over 100 pps. CONCLUSIONS Auditory neurons can be stimulated by a laser beam passing through the round window membrane and driven at rates sufficient for useful auditory information. Optical stimulation and electrical stimulation have different characteristics; which could be selectively exploited in future cochlear implants.
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Affiliation(s)
- Philip D Littlefield
- Department of Surgery, ENT Section, Walter Reed Army Medical Center, Washington, DC 20307-5001, USA
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Shivdasani MN, Mauger SJ, Argent RE, Rathbone GD, Paolini AG. Inferior colliculus responses to dual-site intralamina stimulation in the ventral cochlear nucleus. J Comp Neurol 2010; 518:4226-42. [PMID: 20878785 DOI: 10.1002/cne.22450] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A major limitation of the present auditory brainstem implant (ABI) is its inability to access the tonotopic organization of the ventral cochlear nucleus (VCN). A previous study by our group indicated that stimulation of single sites within a given VCN frequency region did not always elicit frequency-specific responses within the central nucleus of the inferior colliculus (CIC) and in some cases did not elicit a response at all. For this study, we hypothesized that sequential stimulation (with a short interpulse delay of 320 μsec) of two VCN sites in similar frequency regions would enhance responsiveness in CIC neurons. Multiunit neural recordings in response to pure tones were obtained at 58 VCN and 164 CIC sites in anesthetized rats. Among the 58 VCN sites, 39 pairs of sites with similar characteristic frequencies were chosen for electrical stimulation. Each member of a VCN pair was electrically stimulated individually, followed by sequential stimulation of the pair, while recording CIC responses. On average, CIC sites were found to respond to dual-site VCN stimulation with significantly lower thresholds, wider dynamic ranges, a greater extent of activation with increasing current levels, and a higher degree of frequency specificity compared with single-site stimulation. Although these effects were positive for the most part, in some cases dual-site stimulation resulted in increased CIC thresholds and decreased dynamic ranges, extent of activation, and frequency specificity. The results suggest that multisite stimulation within VCN isofrequency laminae using penetrating electrodes could significantly improve ABI stimulation strategies and implant performance.
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Affiliation(s)
- Mohit N Shivdasani
- School of Psychological Science, La Trobe University, Bundoora, Victoria, Australia
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Shivdasani MN, Luu CD, Cicione R, Fallon JB, Allen PJ, Leuenberger J, Suaning GJ, Lovell NH, Shepherd RK, Williams CE. Evaluation of stimulus parameters and electrode geometry for an effective suprachoroidal retinal prosthesis. J Neural Eng 2010; 7:036008. [DOI: 10.1088/1741-2560/7/3/036008] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Excitation patterns of simultaneous and sequential dual-electrode stimulation in cochlear implant recipients. Ear Hear 2009; 30:559-67. [PMID: 19617837 DOI: 10.1097/aud.0b013e3181ab2b6f] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE Both simultaneous (SI) and sequential stimulation of intracochlear electrodes can be used to generate pitches that are intermediate to the physical electrodes (PEs). The goal of this study was to compare the spread of neural excitation for SI and sequential dual-electrode stimulation with the spread of neural excitation for the intermediate electrode using electrically evoked compound action potentials. DESIGN Seven Advanced Bionics cochlear implant users with either CII or HiRes 90k implant and HiFocus 1 or HiFocus 1j electrode array participated in this study. A masker-probe subtraction method was used to derive neural excitation patterns for SI nonadjacent dual-electrode stimulation, apical and basal-first sequential nonadjacent dual-electrode stimulation, and the intermediate PE. For apical-first sequential (SEa) stimulation, the masker pulse on the apical electrode immediately preceded the masker pulse on the basal electrode, and vice versa for basal-first sequential stimulation (SEb). The electrodes used for dual-electrode stimulation were separated by an intermediate PE, which represents a spatial distance of approximately 2 mm. Current levels necessary to achieve comfortable loudness were determined for each masker and probe stimulus. During the evoked compound action potential measurements, the masker was fixed in location, whereas the probe was varied across a subset of electrodes in the array. Neural responses were calculated by subtracting the response to the probe from the masked response. RESULTS Neural excitation patterns were normalized to their peak and analyzed in terms of their area and center of gravity. The area and center of gravity for SI nonadjacent dual-electrode stimulation were similar to those of the intermediate PE. In contrast, the area for the two modes of sequential nonadjacent dual-electrode (SEa and SEb) stimulation differed significantly from the intermediate PE. The center of gravity for SEa stimulation also differed significantly from the intermediate PE, whereas there was no significant difference in the center of gravity between SEb stimulation and the intermediate PE. CONCLUSIONS Peripheral neural activation patterns suggest a similar spread of excitation for SI dual-electrode stimulation and the intermediate PE. The spread of excitation associated with sequential dual-electrode stimulation is generally different from the intermediate PE, and it varies depending on the order of the sequential pulses.
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Kwon BJ, van den Honert C. Spatial and temporal effects of interleaved masking in cochlear implants. J Assoc Res Otolaryngol 2009; 10:447-57. [PMID: 19495879 DOI: 10.1007/s10162-009-0168-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 03/13/2009] [Indexed: 11/29/2022] Open
Abstract
Modern cochlear implants utilize interleaved presentation of pulses on different electrodes to avoid physical interference among multiple current fields, yet neural interaction still exists. In the present study, masking was examined with four Nucleus24 users with the banded electrode array in an interleaved masking paradigm, where a probe stimulus was interleaved with a masker stimulus. Spatial and temporal aspects of masking were addressed by fixing the masker at the middle of the electrode array and changing the location of the probe and by testing various stimulation rates: 125, 500, 2,000, and 6,410 Hz. In addition, growth of masking (GOM) was assessed by changing the masker level in six steps. Results indicated that masking patterns were generally much wider, regardless of stimulation rate, than those in acoustic hearing. The amount of masking decreased from the peak at the rate of approximately 0.5 dB/mm even at the highest masker level. The pattern of GOM with the rates higher than 500 Hz was different from that observed in previous masking studies, characterized by markedly shallow growth at low masker levels or overall shallow growth. A facilitating effect of the masker (lowering the threshold) was suspected, except for the 125-Hz condition, due to the fibers that were subliminally excited, but not discharged, by the masker with local perturbations of membrane potentials, and were subsequently discharged easily by a lower level probe when the temporal gap between masker and probe was sufficiently short. These results suggest that both refractory characteristics of neurons and neural summation be considered in interleaved stimulation of pulses at high, but clinically relevant, stimulation rates. Overall, the present masking study might provide a basis for models in psychophysics and speech understanding in current cochlear implant systems utilizing high-rate interleaved stimulation.
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Affiliation(s)
- Bom Jun Kwon
- Department of Communication Sciences and Disorders, University of Utah, Salt Lake City, UT 84112, USA.
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Kim SJ, Badi AN, Normann RA. Selective Activation of Cat Primary Auditory Cortex by way of Direct Intraneural Auditory Nerve Stimulation. Laryngoscope 2009; 117:1053-62. [PMID: 17545868 DOI: 10.1097/mlg.0b013e31804714a7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES/HYPOTHESIS Although cochlear implants have been successfully used by many individuals with profound hearing impairment, limitations still remain with this approach to hearing restoration, including poor stimulation selectivity because of cross-talk between electrodes and poor low-frequency percepts. These limitations may be mitigated by direct intraneural stimulation of the auditory nerve by way of an array of penetrating microelectrodes. Such an approach should provide focal stimulation and selective activation of the nerve fibers, thereby minimizing cross-talk among implanted stimulating electrodes and evoking narrow-band frequency percepts. STUDY DESIGN We investigated the activation of primary auditory cortex evoked by such direct intraneural electrical stimulation of the auditory nerve. METHODS We implanted 11 penetrating microelectrodes in the cat auditory nerve, simulated the nerve by way of these electrodes, and recorded the evoked neuronal activity patterns in cat primary auditory cortex. We compared these activation patterns with acoustically evoked cortical activity patterns obtained in a different animal. RESULTS Our results showed that direct stimulation of the auditory nerve evoked localized activity patterns in primary auditory cortex similar in spatial extent to those evoked by acoustic stimulation and that the extent of cortical activation by both acoustic and electrical stimuli was graded with stimulus intensity. These results suggest that the implanted electrodes can excite independent and small populations of nerve fibers. CONCLUSION This study demonstrates the functional feasibility of direct intraneural auditory nerve stimulation with an array of penetrating microelectrodes and that such an approach could form the foundation for an auditory prosthesis with improved frequency coding.
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Affiliation(s)
- Seung-Jae Kim
- Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112, USA
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Tehovnik EJ, Slocum WM, Smirnakis SM, Tolias AS. Microstimulation of visual cortex to restore vision. PROGRESS IN BRAIN RESEARCH 2009; 175:347-75. [PMID: 19660667 DOI: 10.1016/s0079-6123(09)17524-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This review argues that one reason why a functional visuo-cortical prosthetic device has not been developed to restore even minimal vision to blind individuals is because there is no animal model to guide the design and development of such a device. Over the past 8 years we have been conducting electrical microstimulation experiments on alert behaving monkeys with the aim of better understanding how electrical stimulation of the striate cortex (area V1) affects oculo- and skeleto-motor behaviors. Based on this work and upon review of the literature, we arrive at several conclusions: (1) As with the development of the cochlear implant, the development of a visuo-cortical prosthesis can be accelerated by using animals to test the perceptual effects of microstimulating V1 in intact and blind monkeys. (2) Although a saccade-based paradigm is very convenient for studying the effectiveness of delivering stimulation to V1 to elicit saccadic eye movements, it is less ideal for probing the volitional state of monkeys, as they perceive electrically induced phosphenes. (3) Electrical stimulation of V1 can delay visually guided saccades generated to a punctate target positioned in the receptive field of the stimulated neurons. We call the region of visual space affected by the stimulation a delay field. The study of delay fields has proven to be an efficient way to study the size and shape of phosphenes generated by stimulation of macaque V1. (4) An alternative approach to ascertain what monkeys see during electrical stimulation of V1 is to have them signal the detection of current with a lever press. Monkeys can readily detect currents of 1-2 microA delivered to V1. In order to evoke featured phosphenes currents of under 5 microA will be necessary. (5) Partially lesioning the retinae of monkeys is superior to completely lesioning the retinae when determining how blindness affects phosphene induction. We finish by proposing a future experimental paradigm designed to determine what monkeys see when stimulation is delivered to V1, by assessing how electrical fields generated through multiple electrodes interact for the production of phosphenes, and by depicting a V1 circuit that could mediate electrically induced phosphenes.
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Affiliation(s)
- Edward J Tehovnik
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
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Hughes ML, Stille LJ. Psychophysical and physiological measures of electrical-field interaction in cochlear implants. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2009; 125:247-60. [PMID: 19173412 PMCID: PMC2633105 DOI: 10.1121/1.3035842] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2008] [Revised: 10/31/2008] [Accepted: 11/03/2008] [Indexed: 05/24/2023]
Abstract
The primary purpose of this study was to determine whether the electrically evoked compound action potential (ECAP) can be used to predict psychophysical electrical-field interaction patterns obtained with simultaneous stimulation of intracochlear electrodes. The second goal was to determine whether ECAP patterns are affected by recording location because differences might influence the relation between ECAP and psychophysical measures. The third goal was to investigate whether symmetrical threshold shifts are produced with phase inversion of the interaction stimulus. Nine adults with Advanced Bionics cochlear implants participated. ECAP and psychophysical thresholds were obtained for basal, middle, and apical probe electrodes in the presence of a subthreshold interaction stimulus delivered simultaneously to each of seven to eight interaction electrodes per probe. The results showed highly significant correlations between ECAP and psychophysical threshold shifts for all nine subjects, which suggests that the ECAP can adequately predict psychophysical electrical-field interaction patterns for subthreshold stimuli. ECAP thresholds were significantly higher for recordings from the basal (versus apical) side of the probe, which suggests that recording location may affect relations between ECAP and psychophysical measures. Interaction stimulus phase inversion generally produced symmetrical threshold shifts for psychophysical measures but not for half of ECAP measures.
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Affiliation(s)
- Michelle L Hughes
- Boys Town National Research Hospital, Lied Learning and Technology Center, Omaha, Nebraska 68131, USA
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Gordon KA, Tanaka S, Wong DDE, Papsin BC. Characterizing responses from auditory cortex in young people with several years of cochlear implant experience. Clin Neurophysiol 2008; 119:2347-62. [PMID: 18752993 DOI: 10.1016/j.clinph.2008.06.013] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2006] [Revised: 06/19/2008] [Accepted: 06/22/2008] [Indexed: 11/24/2022]
Abstract
OBJECTIVE To determine if cortical responses evoked by a cochlear implant in children who are deaf differ from normal and to characterize these differences in children who achieve good versus fair speech perception outcomes post-implantation. METHODS Late latency-evoked potential responses were recorded at 28 scalp locations in 16 children who were deaf from infancy and experienced cochlear implant users. Speech perception measures indicated that 8 had good scores and 8 had fair scores. In each child, responses were evoked by 36ms electrical pulse trains delivered from a single-implant electrode at the apical and basal ends of the array and by 36ms tone bursts (0.5, 2, and 6kHz). Responses to the tone bursts were also recorded in 14 age-matched children with normal hearing. RESULTS We found (1) a dominant positive wave in all implant users and (2) a larger than normal negative amplitude peak in users with fair speech perception scores which had similar scalp topography to N1 but did not show the expected changes in amplitude with stimulus frequency. CONCLUSIONS Late latency-evoked potential responses in children using cochlear implants reflect abnormal and/or immature patterns of cortical activity. SIGNIFICANCE Limitations in auditory skills with a cochlear implant in children may be due to developmental processes in the cortex which are either slow to mature or which mature abnormally.
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Affiliation(s)
- K A Gordon
- The Cochlear Implant Program, The Cochlear Implant Laboratory, Room 6D08, The Hospital for Sick Children, 555 University Avenue, Toronto, Ont., Canada M5G 1X8.
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Middlebrooks JC. Cochlear-implant high pulse rate and narrow electrode configuration impair transmission of temporal information to the auditory cortex. J Neurophysiol 2008; 100:92-107. [PMID: 18450583 PMCID: PMC2493502 DOI: 10.1152/jn.01114.2007] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2007] [Accepted: 04/25/2008] [Indexed: 11/22/2022] Open
Abstract
In the most commonly used cochlear prosthesis systems, temporal features of sound are signaled by amplitude modulation of constant-rate pulse trains. Several convincing arguments predict that speech reception should be optimized by use of pulse rates > or approximately 2,000 pulses per second (pps) and by use of intracochlear electrode configurations that produce restricted current spread (e.g., bipolar rather than monopolar configurations). Neither of those predictions has been borne out in consistent improvements in speech reception. Neurons in the auditory cortex of anesthetized guinea pigs phase lock to the envelope of sine-modulated electric pulse trains presented through a cochlear implant. The present study used that animal model to quantify the effects of carrier pulse rate, electrode configuration, current level, and modulator wave shape on transmission of temporal information from a cochlear implant to the auditory cortex. Modulation sensitivity was computed using a signal-detection analysis of cortical phase-locking vector strengths. Increasing carrier pulse rate in 1-octave steps from 254 to 4,069 pps resulted in systematic decreases in sensitivity. Comparison of sine- versus square-wave modulator waveforms demonstrated that some, but not all, of the loss of modulation sensitivity at high pulse rates was a result of the decreasing size of pulse-to-pulse current steps at the higher rates. Use of a narrow bipolar electrode configuration, compared with the monopolar configuration, produced a marked decrease in modulation sensitivity. Results from this animal model suggest explanations for the failure of high pulse rates and/or bipolar electrode configurations to produce hoped-for improvements in speech reception.
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Affiliation(s)
- John C Middlebrooks
- Department of Otolaryngology Head and Neck Surgery, Kresge Hearing Research Institute, University of Michigan, Ann Arbor, Michigan, USA.
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Bonham BH, Litvak LM. Current focusing and steering: modeling, physiology, and psychophysics. Hear Res 2008; 242:141-53. [PMID: 18501539 DOI: 10.1016/j.heares.2008.03.006] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Revised: 03/20/2008] [Accepted: 03/25/2008] [Indexed: 11/25/2022]
Abstract
Current steering and current focusing are stimulation techniques designed to increase the number of distinct perceptual channels available to cochlear implant (CI) users by adjusting currents applied simultaneously to multiple CI electrodes. Previous studies exploring current steering and current focusing stimulation strategies are reviewed, including results of research using computational models, animal neurophysiology, and human psychophysics. Preliminary results of additional neurophysiological and human psychophysical studies are presented that demonstrate the success of current steering strategies in stimulating auditory nerve regions lying between physical CI electrodes, as well as current focusing strategies that excite regions narrower than those stimulated using monopolar configurations. These results are interpreted in the context of perception and speech reception by CI users. Disparities between results of physiological and psychophysical studies are discussed. The differences in stimulation used for physiological and psychophysical studies are hypothesized to contribute to these disparities. Finally, application of current steering and focusing strategies to other types of auditory prostheses is also discussed.
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Affiliation(s)
- Ben H Bonham
- Saul and Ida Epstein Laboratory, Department of Otolaryngology-HNS, 533 Parnassus Avenue, Box 0526, University of California, San Francisco, CA 94143-0526, USA.
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Gordon KA, Papsin BC, Harrison RV. Auditory brainstem activity and development evoked by apical versus basal cochlear implant electrode stimulation in children. Clin Neurophysiol 2007; 118:1671-84. [PMID: 17588811 DOI: 10.1016/j.clinph.2007.04.030] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2006] [Revised: 04/17/2007] [Accepted: 04/30/2007] [Indexed: 11/21/2022]
Abstract
OBJECTIVE The role of apical versus basal cochlear implant electrode stimulation on central auditory development was examined. We hypothesized that, in children with early onset deafness, auditory development evoked by basal electrode stimulation would differ from that evoked more apically. METHODS Responses of the auditory nerve and brainstem, evoked by an apical and a basal implant electrode, were measured over the first year of cochlear implant use in 50 children with early onset severe to profound deafness who used hearing aids prior to implantation. RESULTS Responses at initial stimulation were of larger amplitude and shorter latency when evoked by the apical electrode. No significant effects of residual hearing or age were found on initial response amplitudes or latencies. With implant use, responses evoked by both electrodes showed decreases in wave and interwave latencies reflecting decreased neural conduction time through the brainstem. Apical versus basal differences persisted with implant experience with one exception; eIII-eV interlatency differences decreased with implant use. CONCLUSIONS Acute stimulation shows prolongation of basally versus apically evoked auditory nerve and brainstem responses in children with severe to profound deafness. Interwave latencies reflecting neural conduction along the caudal and rostral portions of the brainstem decreased over the first year of implant use. Differences in neural conduction times evoked by apical versus basal electrode stimulation persisted in the caudal but not rostral brainstem. SIGNIFICANCE Activity-dependent changes of the auditory brainstem occur in response to both apical and basal cochlear implant electrode stimulation.
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Affiliation(s)
- K A Gordon
- Cochlear Implant Laboratory, the Hospital for Sick Children, and Department of Otolaryngology-Head and Neck Surgery, University of Toronto, Ontario, Canada.
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34
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Middlebrooks JC, Snyder RL. Auditory prosthesis with a penetrating nerve array. J Assoc Res Otolaryngol 2007; 8:258-79. [PMID: 17265124 PMCID: PMC2538356 DOI: 10.1007/s10162-007-0070-2] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Accepted: 12/15/2006] [Indexed: 11/28/2022] Open
Abstract
Contemporary auditory prostheses ("cochlear implants") employ arrays of stimulating electrodes implanted in the scala tympani of the cochlea. Such arrays have been implanted in some 100,000 profoundly or severely deaf people worldwide and arguably are the most successful of present-day neural prostheses. Nevertheless, most implant users show poor understanding of speech in noisy backgrounds, poor pitch recognition, and poor spatial hearing, even when using bilateral implants. Many of these limitations can be attributed to the remote location of stimulating electrodes relative to excitable cochlear neural elements. That is, a scala tympani electrode array lies within a bony compartment filled with electrically conductive fluid. Moreover, scala tympani arrays typically do not extend to the apical turn of the cochlea in which low frequencies are represented. In the present study, we have tested in an animal model an alternative to the conventional cochlear implant: a multielectrode array implanted directly into the auditory nerve. We monitored the specificity of stimulation of the auditory pathway by recording extracellular unit activity at 32 sites along the tonotopic axis of the inferior colliculus. The results demonstrate the activation of specific auditory nerve populations throughout essentially the entire frequency range that is represented by characteristic frequencies in the inferior colliculus. Compared to conventional scala tympani stimulation, thresholds for neural excitation are as much as 50-fold lower and interference between electrodes stimulated simultaneously is markedly reduced. The results suggest that if an intraneural stimulating array were incorporated into an auditory prosthesis system for humans, it could offer substantial improvement in hearing replacement compared to contemporary cochlear implants.
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Affiliation(s)
- John C. Middlebrooks
- Kresge Hearing Research Institute, Department of Otorhinolaryngology, University of Michigan, Ann Arbor, MI 48109-0506 USA
| | - Russell L. Snyder
- Epstein Laboratory, Department of Otolaryngology, Head and Neck Surgery, University of California, San Francisco, CA 94143-0526 USA
- Department of Psychology, Utah State University, Logan, UT 84322-2810 USA
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Arnoldner C, Riss D, Baumgartner WD, Kaider A, Hamzavi JS. Cochlear Implant Channel Separation and Its Influence on Speech Perception – Implications for a New Electrode Design. Audiol Neurootol 2007; 12:313-24. [PMID: 17536200 DOI: 10.1159/000103212] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2006] [Accepted: 03/30/2007] [Indexed: 11/19/2022] Open
Abstract
There are a variety of factors which can influence cochlear implantation outcome. Channel interaction is one of the variables responsible for audiological performance deterioration in multichannel implants. Electrode design is--among others--one way to decrease the incidence of channel interaction. At present, electrodes differ in overall length, diameter, contact design and distribution, but none of the electrodes available have a distinct variability in the amount of space between contacts across the length of the electrode. The aim of this study was to investigate whether a new electrode design featuring larger contact spacing in the apical part of deeply inserted electrodes would lead to an increase in speech perception. Eighteen postlingually deafened patients fitted with MedEl Combi 40+ or MedEl Pulsar cochlear implants using the MedEl implementation of continuous interleaved sampling participated in this study. Patients were tested in 6 conditions, in which the channel spacing and distribution of electrode contacts in each patient were artificially varied by activating or deactivating different channels. Performance was tested immediately after each change in setup with a monosyllable and sentence test (Hochmaier, Schultz and Moser). Our results showed that the condition with the highest distance between contacts in the apical part (up to 6.4 mm instead of 2.4 mm) is the most effective for the matched map condition: the results improved statistically significantly for the sentence test from 72% in the standard 12-channel condition to 83.2% and from 40.8 to 50% for the monosyllable test. Based on these findings, we present a new electrode design which can help achieve further increases in speech perception with cochlear implants.
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Affiliation(s)
- Christoph Arnoldner
- Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria
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36
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Bierer JA. Threshold and channel interaction in cochlear implant users: evaluation of the tripolar electrode configuration. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2007; 121:1642-53. [PMID: 17407901 DOI: 10.1121/1.2436712] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The efficacy of cochlear implants is limited by spatial and temporal interactions among channels. This study explores the spatially restricted tripolar electrode configuration and compares it to bipolar and monopolar stimulation. Measures of threshold and channel interaction were obtained from nine subjects implanted with the Clarion HiFocus-I electrode array. Stimuli were biphasic pulses delivered at 1020 pulses/s. Threshold increased from monopolar to bipolar to tripolar stimulation and was most variable across channels with the tripolar configuration. Channel interaction, quantified by the shift in threshold between single- and two-channel stimulation, occurred for all three configurations but was largest for the monopolar and simultaneous conditions. The threshold shifts with simultaneous tripolar stimulation were slightly smaller than with bipolar and were not as strongly affected by the timing of the two channel stimulation as was monopolar. The subjects' performances on clinical speech tests were correlated with channel-to-channel variability in tripolar threshold, such that greater variability was related to poorer performance. The data suggest that tripolar channels with high thresholds may reveal cochlear regions of low neuron survival or poor electrode placement.
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Affiliation(s)
- Julie Arenberg Bierer
- Department of Speech and Hearing Sciences, University of Washington, 1417 NE 42nd Street, Box 354875, Seattle, Washington 98105-6246, USA.
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37
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Carlyon RP, Long CJ, Deeks JM, McKay CM. Concurrent sound segregation in electric and acoustic hearing. J Assoc Res Otolaryngol 2007; 8:119-33. [PMID: 17216383 PMCID: PMC2538412 DOI: 10.1007/s10162-006-0068-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Accepted: 12/04/2006] [Indexed: 10/23/2022] Open
Abstract
We investigated potential cues to sound segregation by cochlear implant (CI) and normal-hearing (NH) listeners. In each presentation interval of experiment 1a, CI listeners heard a mixture of four pulse trains applied concurrently to separate electrodes, preceded by a "probe" applied to a single electrode. In one of these two intervals, which the subject had to identify, the probe electrode was the same as a "target" electrode in the mixture. The pulse train on the target electrode had a higher level than the others in the mixture. Additionally, it could be presented either with a 200-ms onset delay, at a lower rate, or with an asynchrony produced by delaying each pulse by about 5 ms re those on the nontarget electrodes. Neither the rate difference nor the asynchrony aided performance over and above the level difference alone, but the onset delay produced a modest improvement. Experiment 1b showed that two subjects could perform the task using the onset delay alone, with no level difference. Experiment 2 used a method similar to that of experiment 1, but investigated the onset cue using NH listeners. In one condition, the mixture consisted of harmonics 5 to 40 of a 100-Hz fundamental, with the onset of either harmonics 13 to 17 or 26 to 30 delayed re the rest. Performance was modest in this condition, but could be improved markedly by using stimuli containing a spectral gap between the target and nontarget harmonics. The results suggest that (a) CI users are unlikely to use temporal pitch differences between adjacent channels to separate concurrent sounds, and that (b) they can use onset differences between channels, but the usefulness of this cue will be compromised by the spread of excitation along the nerve-fiber array. This deleterious effect of spread-of-excitation can also impair the use of onset cues by NH listeners.
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Affiliation(s)
- Robert P Carlyon
- MRC Cognition & Brain Sciences Unit, 15 Chaucer Rd, Cambridge, CB2 7EF, England.
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38
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Tehovnik EJ, Slocum WM. Phosphene induction by microstimulation of macaque V1. ACTA ACUST UNITED AC 2006; 53:337-43. [PMID: 17173976 PMCID: PMC1850969 DOI: 10.1016/j.brainresrev.2006.11.001] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Revised: 11/01/2006] [Accepted: 11/02/2006] [Indexed: 11/25/2022]
Abstract
Non-human primates are being used to develop a cortical visual prosthesis for the blind. We use the properties of electrical microstimulation of striate cortex (area V1) of macaque monkeys to make inferences about phosphene induction. Our analysis is based on well-established properties of V1: retino-cortical magnification factor, receptive-field size, and the characteristics of hypercolumns. We argue that phosphene size is dependent on the amount of current delivered to V1 and on the retino-cortical magnification factor. We suggest that to improve the correspondence between the site of stimulation within V1 and the visual field location of an elicited phosphene both eyes must be put under experimental control given that phosphene location is retinocentric and given that the vergence angle between the eyes might affect the position of a phosphene in depth. Knowing how electrical microstimulation interacts with cortical tissue to evoke percepts in behaving macaque monkeys is fundamental to the establishment of an effective cortical visual prosthesis for the blind.
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Affiliation(s)
- Edward J Tehovnik
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 USA.
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Tehovnik EJ, Tolias AS, Sultan F, Slocum WM, Logothetis NK. Direct and indirect activation of cortical neurons by electrical microstimulation. J Neurophysiol 2006; 96:512-21. [PMID: 16835359 DOI: 10.1152/jn.00126.2006] [Citation(s) in RCA: 240] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Electrical microstimulation has been used to elucidate cortical function. This review discusses neuronal excitability and effective current spread estimated by using three different methods: 1) single-cell recording, 2) behavioral methods, and 3) functional magnetic resonance imaging (fMRI). The excitability properties of the stimulated elements in neocortex obtained using these methods were found to be comparable. These properties suggested that microstimulation activates the most excitable elements in cortex, that is, by and large the fibers of the pyramidal cells. Effective current spread within neocortex was found to be greater when measured with fMRI compared with measures based on single-cell recording or behavioral methods. The spread of activity based on behavioral methods is in close agreement with the spread based on the direct activation of neurons (as opposed to those activated synaptically). We argue that the greater activation with imaging is attributed to transynaptic spread, which includes subthreshold activation of sites connected to the site of stimulation. The definition of effective current spread therefore depends on the neural event being measured.
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Affiliation(s)
- E J Tehovnik
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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Başkent D. Speech recognition in normal hearing and sensorineural hearing loss as a function of the number of spectral channels. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2006; 120:2908-25. [PMID: 17139748 DOI: 10.1121/1.2354017] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Speech recognition by normal-hearing listeners improves as a function of the number of spectral channels when tested with a noiseband vocoder simulating cochlear implant signal processing. Speech recognition by the best cochlear implant users, however, saturates around eight channels and does not improve when more electrodes are activated, presumably due to reduced frequency selectivity caused by channel interactions. Listeners with sensorineural hearing loss may also have reduced frequency selectivity due to cochlear damage and the resulting reduction in the nonlinear cochlear mechanisms. The present study investigates whether such a limitation in spectral information transmission would be observed with hearing-impaired listeners, similar to implant users. To test the hypothesis, hearing-impaired subjects were selected from a population of patients with moderate hearing loss of cochlear origin, where the frequency selectivity would be expected to be poorer compared to normal hearing. Hearing-impaired subjects were tested for vowel and consonant recognition in steady-state background noise of varying levels using a noiseband vocoder and as a function of the number of spectral channels. For comparison, normal-hearing subjects were tested with the same stimuli at different presentation levels. In quiet and low background noise, performance by normal-hearing and hearing-impaired subjects was similar. In higher background noise, performance by hearing-impaired subjects saturated around eight channels, while performance by normal-hearing subjects continued to increase up to 12-16 channels with vowels, and 10-12 channels with consonants. A similar trend was observed for most of the presentation levels at which the normal-hearing subjects were tested. Therefore, it is unlikely that the effects observed with hearing-impaired subjects were due to insufficient audibility or high presentation levels. Consequently, the results with hearing-impaired subjects were similar to previous results obtained with implant users, but only for background noise conditions.
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Affiliation(s)
- Deniz Başkent
- House Ear Institute, Department of Auditory Implants, 2100 West Third Street, Los Angeles, California 90057, USA.
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41
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Kwon BJ, van den Honert C. Effect of electrode configuration on psychophysical forward masking in cochlear implant listeners. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2006; 119:2994-3002. [PMID: 16708955 DOI: 10.1121/1.2184128] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Bipolar stimulation has been thought to be more beneficial than monopolar stimulation for speech coding in cochlear implants, on the basis of its more restricted current flow. The present study examined whether bipolar stimulation would indeed lead to reduced channel interaction in a behavioral forward masking experiment tested in four Nucleus 24 users. The masker was fixed on one channel and three masker levels that were balanced for loudness between the configurations were chosen. As expected, masking was maximal when the masker and probe channels were spatially close and decreased as they were separated. However, overall masking patterns did not consistently demonstrate sharper tuning with bipolar stimulation than monopolar. This implies that the spatial extent of a bipolar current field is not consistently narrower than that of an equally loud monopolar stimulus; therefore, it should not be assumed that bipolar stimulation leads to reduced channel interaction. Notably, bipolar masking patterns appeared to display more variations across channels, possibly influenced more by anatomical and neural irregularities near electrode contacts than monopolar masking patterns. The present psychophysical results provide a theoretical basis regarding the widespread use (and success) of monopolar configurations by implant users.
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Affiliation(s)
- Bom Jun Kwon
- Cochlear Americas, 400 Inverness Parkway, Suite 400, Englewood, Colorado 80112, USA.
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Tang Q, Liu S, Zeng FG. Loudness adaptation in acoustic and electric hearing. J Assoc Res Otolaryngol 2006; 7:59-70. [PMID: 16425088 PMCID: PMC2504588 DOI: 10.1007/s10162-005-0023-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2005] [Accepted: 11/29/2005] [Indexed: 10/25/2022] Open
Abstract
The present study is aimed to evaluate and compare loudness adaptation between normal hearing and cochlear-implant subjects. Loudness adaptation for 367-s pure tones was measured in five normal-hearing subjects at three frequencies (125, 1,000, and 8,000 Hz) and three levels (30, 60, and 90 dB SPL). In addition, loudness adaptation for 367-s pulse trains was measured in five Clarion cochlear-implant subjects at three stimulation rates (100, 991, and 4,296 Hz), three levels (10, 50, and 90% of the electric dynamic range), three stimulation positions (apical, middle and basal), and two stimulation modes (monopolar and bipolar). The method of successive magnitude estimation was used to quantify loudness adaptation. Similar to the previous results, we found that loudness adaptation in normal-hearing subjects increases with decreasing level and increasing frequency. However, we also found a small but significant loudness enhancement at 90 dB SPL in acoustic hearing. Despite large individual variability, we found that loudness adaptation in cochlear-implant subjects increases with decreasing levels, but is not significantly affected by the rate, place and mode of stimulation. A phenomenological model was proposed to predict loudness adaptation as a function of stimulus frequency and level in acoustic hearing. The present results were not fully compatible with either the restricted excitation hypothesis or the neural adaptation hypothesis. Loudness adaptation may have a central component that is dependent on the peripheral excitation pattern.
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Affiliation(s)
- Qing Tang
- Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697 USA
- Department of Biomedical Engineering, University of California, Irvine, CA 92697 USA
- Department of Cognitive Sciences and Otolaryngology–Head and Neck Surgery, University of California, Irvine, CA 92697 USA
- Hearing and Speech Research Laboratory, University of California, 364 Med Surge II, Irvine, CA 92697-1275 USA
| | - Sheng Liu
- Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697 USA
- Department of Biomedical Engineering, University of California, Irvine, CA 92697 USA
- Department of Cognitive Sciences and Otolaryngology–Head and Neck Surgery, University of California, Irvine, CA 92697 USA
| | - Fan-Gang Zeng
- Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697 USA
- Department of Biomedical Engineering, University of California, Irvine, CA 92697 USA
- Department of Cognitive Sciences and Otolaryngology–Head and Neck Surgery, University of California, Irvine, CA 92697 USA
- Hearing and Speech Research Laboratory, University of California, 364 Med Surge II, Irvine, CA 92697-1275 USA
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Xu L, Zwolan TA, Thompson CS, Pfingst BE. Efficacy of a cochlear implant simultaneous analog stimulation strategy coupled with a monopolar electrode configuration. Ann Otol Rhinol Laryngol 2006; 114:886-93. [PMID: 16363059 DOI: 10.1177/000348940511401113] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVES The present study was performed to evaluate the efficacy and clinical feasibility of using monopolar stimulation with the Clarion Simultaneous Analog Stimulation (SAS) strategy in patients with cochlear implants. METHODS Speech recognition by 10 Clarion cochlear implant users was evaluated by means of 4 different speech processing strategy/electrode configuration combinations; ie, SAS and Continuous Interleaved Sampling (CIS) strategies were each used with monopolar (MP) and bipolar (BP) electrode configurations. The test measures included consonants, vowels, consonant-nucleus-consonant words, and Hearing in Noise Test sentences with a +10 dB signal-to-noise ratio. Additionally, subjective judgments of sound quality were obtained for each strategy/configuration combination. RESULTS All subjects but 1 demonstrated open-set speech recognition with the SAS/MP combination. The group mean Hearing in Noise Test sentence score for the SAS/MP combination was 31.6% (range, 0% to 92%) correct, as compared to 25.0%, 46.7%, and 37.8% correct for the CIS/BP, CIS/MP, and SAS/BP combinations, respectively. Intersubject variability was high, and there were no significant differences in mean speech recognition scores or mean preference ratings among the 4 strategy/configuration combinations tested. Individually, the best speech recognition performance was with the subject's everyday strategy/configuration combination in 72% of the applicable cases. If the everyday strategy was excluded from the analysis, the subjects performed best with the SAS/MP combination in 37.5% of the remaining cases. CONCLUSIONS The SAS processing strategy with an MP electrode configuration gave reasonable speech recognition in most subjects, even though subjects had minimal previous experience with this strategy/configuration combination. The SAS/MP combination might be particularly appropriate for patients for whom a full dynamic range of electrical hearing could not be achieved with a BP configuration.
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Affiliation(s)
- Li Xu
- Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan, Ann Arbor, Michigan, USA
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Abstract
Cochlear implants are very successful devices: more than 60000 people use them throughout the world. Key to the success of these prostheses is the development of electrode arrays that place contacts close to the target neurons, survive for decades in the tissues of the inner ear, and that provide reliable and repeatable excitation to the cells of the auditory nerve. This article describes the early electrode arrays and their development into the arrays that are used presently in clinical cochlear prostheses. While integrated circuit techniques were proposed and tested in the laboratory two decades ago, the present clinical devices still are hand built and made of wire-based technologies. Current approaches that seek to automate the construction of cochlear electrode arrays are described and discussed.
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Chatterjee M, Galvin JJ, Fu QJ, Shannon RV. Effects of stimulation mode, level and location on forward-masked excitation patterns in cochlear implant patients. J Assoc Res Otolaryngol 2005; 7:15-25. [PMID: 16270234 PMCID: PMC2504584 DOI: 10.1007/s10162-005-0019-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 09/28/2005] [Indexed: 10/25/2022] Open
Abstract
In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in the cochlea to approximate the spatial representation of speech. Theoretically, electrode configurations that restrict the current spread within the cochlea (e.g., bi- or tri-polar stimulation) may provide better spatial selectivity, and in turn, better speech recognition than configurations that produce a broader current spread (e.g., monopolar stimulation). However, the effects of electrode configuration on supra-threshold excitation patterns have not been systematically studied in cochlear implant patients. In the present study, forward-masked excitation patterns were measured in cochlear implant patients as functions of stimulation mode, level and location within the cochlea. All stimuli were 500 pulses-per-second biphasic pulse trains (200 micros/phase, 20 micros inter-phase gap). Masker stimuli were 200 ms in duration; the bi-polar configuration was varied from narrow (BP+1) to wide (BP+17), depending on the test condition. Probe stimuli were 20 ms in duration and the masker-probe delay was 5 ms; the probe configuration was fixed at BP+1. The results indicated that as the distance between the active and return electrodes in a bi-polar pair was increased, the excitation pattern broadened within the cochlea. When the distance between active and return electrodes was sufficiently wide, two peaks were often observed in the excitation pattern, comparable to non-overlapping electric fields produced by widely separated dipoles. Analyses of the normalized data showed little effect of stimulation level on the shape of the excitation pattern.
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Affiliation(s)
- Monita Chatterjee
- Department of Auditory Implants and Perception, House Ear Institute, 2100 W. Third St., Los Angeles, CA 90057, USA.
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Abstract
Cochlear implants provide functional hearing to the majority of recipients and have gained widespread acceptance clinically, but the range of performance remains great and largely unexplained. Designs for implanted electrodes and electronics have converged, whereas novel speech processing strategies have proliferated. For each patient, the fitting audiologist must sort empirically through options that produce large but idiosyncratic differences in both objective performance and subjective preference. This review and analysis suggests that the place-pitch and rate-pitch theories on which cochlear implants have been designed are incomplete. The missing component may be related to the phase-locking of auditory nerve activity to both acoustic and electrical stimulation. This component is likely to be highly distorted by electrical stimulation but its importance as one of several different pitch encoding mechanisms may vary widely among patients. Systematic means to control these putative phase effects using modern, high-speed, and high-density cochlear implants may make it possible to identify more efficiently the best strategy for a given patient and to minimize the perceptual confusion that arises from conflicting cues.
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Affiliation(s)
- Gerald E Loeb
- Department of Biomedical Engineering, Viterbi School of Engineering and A. E. Mann Institute for Biomedical Engineering, University of Southern California, Los Angeles 90089-1112, USA.
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Müller J. Technical devices for hearing-impaired individuals: cochlear implants and brain stem implants - developments of the last decade. GMS CURRENT TOPICS IN OTORHINOLARYNGOLOGY, HEAD AND NECK SURGERY 2005; 4:Doc04. [PMID: 22073052 PMCID: PMC3200995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Over the past two decades, the fascinating possibilities of cochlear implants for congenitally deaf or deafened children and adults developed tremendously and created a rapidly developing interdisciplinary research field.The main advancements of cochlear implantation in the past decade are marked by significant improvement of hearing and speech understanding in CI users. These improvements are attributed to the enhancement of speech coding strategies.The Implantation of more (and increasingly younger) children as well as the possibilities of the restoration of binaural hearing abilities with cochlear implants reflect the high standards reached by this development. Despite this progress, modern cochlear implants do not yet enable normal speech understanding, not even for the best patients. In particular speech understanding in noise remains problematic [1]. Until the mid 1990ies research concentrated on unilateral implantation. Remarkable and effective improvements have been made with bilateral implantation since 1996. Nowadays an increasing numbers of patients enjoy these benefits.
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Affiliation(s)
- Joachim Müller
- Schwerpunkt Cochlea Implantate und Hörprothetik, Klinik und Poliklinik für Hals-, Nasen- und Ohrenkranke der Universität Würzburg
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Middlebrooks JC, Bierer JA, Snyder RL. Cochlear implants: the view from the brain. Curr Opin Neurobiol 2005; 15:488-93. [PMID: 16009544 DOI: 10.1016/j.conb.2005.06.004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Accepted: 06/30/2005] [Indexed: 10/25/2022]
Abstract
The cochlear implant arguably is the most successful neural prosthesis. Studies of the responses of the central auditory system to prosthetic electrical stimulation of the cochlea are revealing the success with which electrical stimulation of a deaf ear can mimic acoustic stimulation of a normal-hearing ear. Understanding of the physiology of central auditory structures can lead to improved restoration of hearing with cochlear implants. In turn, the cochlear implant can be exploited as an experimental tool for examining central hearing mechanisms isolated from the effects of cochlear mechanics and transduction.
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Affiliation(s)
- John C Middlebrooks
- Kresge Hearing Research Institute, University of Michigan, 1301 East Ann Street, Ann Arbor, MI 48109-0506, USA.
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Eisen MD, Franck KH. Electrode interaction in pediatric cochlear implant subjects. J Assoc Res Otolaryngol 2005; 6:160-70. [PMID: 15952052 PMCID: PMC2538331 DOI: 10.1007/s10162-005-5057-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2004] [Accepted: 02/16/2005] [Indexed: 10/25/2022] Open
Abstract
Multielectrode cochlear implants rely on differential stimulation of the cochlear nerve for presenting the brain with the spectral and timing information required to understand speech. In implant patients, the degree of overlap among cochlear nerve fibers stimulated by the different electrodes constitutes the electrode interaction. Electrode interaction degrades the spectral resolution of the implant's stimulus. We sought to define electrode interaction in a cohort of pediatric cochlear implant subjects as a function of both stimulus intensity and electrode location along the array. The 27 pediatric subjects that completed the study were implanted with either the Clarion Hi-Focus array with or without positioner, the Nucleus 24 Contour array, or the Nucleus 24 Straight array. All but two of the patients had congenital hearing loss, and none of the patients had meningitis prior to the onset of deafness. The cochlear nerve response was measured with the electrically evoked compound action potential (ECAP). A forward masking protocol was used such that a probe stimulus electrode remained fixed while a preceding masker was moved across the array. Electrode interaction was estimated by measuring the unmasked probe response minus the masked probe response. Three probe locations and three probe intensities were examined for each subject. At all probe locations, electrode interaction increased as probe intensity increased (p < 0.05). Interaction at the basal probe was less than that at either the middle or apical probe locations (p < 0.05), and significant correlation found between probe distance from the basal end of the array and electrode interaction (p < 0.001). These results demonstrate that in this cohort of pediatric subjects, electrode interaction depended on both stimulus intensity and probe location. Implications of these findings on future implant array design and current implant fitting strategies are discussed. The impact of electrode interaction on implant performance is yet to be elucidated.
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Affiliation(s)
- Marc D Eisen
- Center for Childhood Communication, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
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Middlebrooks JC. Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2004; 116:452-68. [PMID: 15296005 DOI: 10.1121/1.1760795] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Interactions among the multiple channels of a cochlear prosthesis limit the number of channels of information that can be transmitted to the brain. This study explored the influence on channel interactions of electrical pulse rates and temporal offsets between channels. Anesthetized guinea pigs were implanted with 2-channel scala-tympani electrode arrays, and spike activity was recorded from the auditory cortex. Channel interactions were quantified as the reduction of the threshold for pulse-train stimulation of the apical channel by sub-threshold stimulation of the basal channel. Pulse rates were 254 or 4069 pulses per second (pps) per channel. Maximum threshold reductions averaged 9.6 dB when channels were stimulated simultaneously. Among nonsimultaneous conditions, threshold reductions at the 254-pps rate were entirely eliminated by a 1966-micros inter-channel offset. When offsets were only 41 to 123 micros, however, maximum threshold shifts averaged 3.1 dB, which was comparable to the dynamic ranges of cortical neurons in this experimental preparation. Threshold reductions at 4069 pps averaged up to 1.3 dB greater than at 254 pps, which raises some concern in regard to high-pulse-rate speech processors. Thresholds for various paired-pulse stimuli, pulse rates, and pulse-train durations were measured to test possible mechanisms of temporal integration.
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Affiliation(s)
- John C Middlebrooks
- Kresge Hearing Research Institute, Department of Otorhinolaryngology, University of Michigan Medical School, 1301 E. Ann St., Ann Arbor, Michigan 48109-0506, USA.
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