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Chen J, Sprigg J, Castle N, Matson C, Hedjoudje A, Dai C. A Virtual Inner Ear Model Selects Ramped Pulse Shapes for Vestibular Afferent Stimulation. Bioengineering (Basel) 2023; 10:1436. [PMID: 38136027 PMCID: PMC10740892 DOI: 10.3390/bioengineering10121436] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 12/03/2023] [Accepted: 12/12/2023] [Indexed: 12/24/2023] Open
Abstract
Bilateral vestibular deficiency (BVD) results in chronic dizziness, blurry vision when moving the head, and postural instability. Vestibular prostheses (VPs) show promise as a treatment, but the VP-restored vestibulo-ocular reflex (VOR) gain in human trials falls short of expectations. We hypothesize that the slope of the rising ramp in stimulation pulses plays an important role in the recruitment of vestibular afferent units. To test this hypothesis, we utilized customized programming to generate ramped pulses with different slopes, testing their efficacy in inducing electrically evoked compound action potentials (eCAPs) and current spread via bench tests and simulations in a virtual inner model created in this study. The results confirmed that the slope of the ramping pulses influenced the recruitment of vestibular afferent units. Subsequently, an optimized stimulation pulse train was identified using model simulations, exhibiting improved modulation of vestibular afferent activity. This optimized slope not only reduced the excitation spread within the semicircular canals (SCCs) but also expanded the neural dynamic range. While the model simulations exhibited promising results, in vitro and in vivo experiments are warranted to validate the findings of this study in future investigations.
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Affiliation(s)
- Joseph Chen
- Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019, USA
- School of Medicine and Biomedical Engineering, University of Oklahoma, Norman, OK 73019, USA
| | - Jayden Sprigg
- Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019, USA
| | - Nicholas Castle
- Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019, USA
| | - Cayman Matson
- School of Medicine and Biomedical Engineering, University of Oklahoma, Norman, OK 73019, USA
| | | | - Chenkai Dai
- Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019, USA
- School of Medicine and Biomedical Engineering, University of Oklahoma, Norman, OK 73019, USA
- Biomedical Engineering Department, Johns Hopkins University, Baltimore, MD 21218, USA
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Garadat SN, Colesa DJ, Swiderski DL, Raphael Y, Pfingst BE. Estimating health of the implanted cochlea using psychophysical strength-duration functions and electrode configuration. Hear Res 2022; 414:108404. [PMID: 34883366 PMCID: PMC8761176 DOI: 10.1016/j.heares.2021.108404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 11/17/2021] [Accepted: 11/25/2021] [Indexed: 02/03/2023]
Abstract
It is generally believed that the efficacy of cochlear implants is partly dependent on the condition of the stimulated neural population. Cochlear pathology is likely to affect the manner in which neurons respond to electrical stimulation, potentially resulting in differences in perception of electrical stimuli across cochlear implant recipients and across the electrode array in individual cochlear implant users. Several psychophysical and electrophysiological measures have been shown to predict cochlear health in animals and were used to assess conditions near individual stimulation sites in humans. In this study, we examined the relationship between psychophysical strength-duration functions and spiral ganglion neuron density in two groups of guinea pigs with cochlear implants who had minimally-overlapping cochlear health profiles. One group was implanted in a hearing ear (N = 10) and the other group was deafened by cochlear perfusion of neomycin, inoculated with an adeno-associated viral vector with an Ntf3-gene insert (AAV.Ntf3) and implanted (N = 14). Psychophysically measured strength-duration functions for both monopolar and tripolar electrode configurations were then compared for the two treatment groups. Results were also compared to their histological outcomes. Overall, there were considerable differences between the two treatment groups in terms of their psychophysical performance as well as the relation between their functional performance and histological data. Animals in the neomycin-deafened, neurotrophin-treated, and implanted group (NNI) exhibited steeper strength-duration function slopes; slopes were positively correlated with SGN density (steeper slopes in animals that had higher SGN densities). In comparison, the implanted hearing (IH) group had shallower slopes and there was no relation between slopes and spiral ganglion density. Across all animals, slopes were negatively correlated with ensemble spontaneous activity levels (shallower slopes with higher ensemble spontaneous activity levels). We hypothesize that differences in strength-duration function slopes between the two treatment groups were related to the condition of the inner hair cells, which generate spontaneous activity that could affect the across-fiber synchrony and/or the size of the population of neural elements responding to electrical stimulation. In addition, it is likely that spiral ganglion neuron peripheral processes were present in the IH group, which could affect membrane properties of the stimulated neurons. Results suggest that the two treatment groups exhibited distinct patterns of variation in conditions near the stimulating electrodes that altered detection thresholds. Overall, the results of this study suggest a complex relationship between psychophysical detection thresholds for cochlear implant stimulation and nerve survival in the implanted cochlea. This relationship seems to depend on the characteristics of the electrical stimulus, the electrode configuration, and other biological features of the implanted cochlea such as the condition of the inner hair cells and the peripheral processes.
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Affiliation(s)
- Soha N. Garadat
- Department of Hearing and Speech Sciences, The University of Jordan, Amman, 11942, Jordan,Kresge Hearing Research Institute, Department of Otolaryngology—Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109-5616, USA
| | - Deborah J. Colesa
- Kresge Hearing Research Institute, Department of Otolaryngology—Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109-5616, USA
| | - Donald L. Swiderski
- Kresge Hearing Research Institute, Department of Otolaryngology—Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109-5616, USA
| | - Yehoash Raphael
- Kresge Hearing Research Institute, Department of Otolaryngology—Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109-5616, USA
| | - Bryan E. Pfingst
- Kresge Hearing Research Institute, Department of Otolaryngology—Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109-5616, USA
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Carlyon RP, Goehring T. Cochlear Implant Research and Development in the Twenty-first Century: A Critical Update. J Assoc Res Otolaryngol 2021; 22:481-508. [PMID: 34432222 PMCID: PMC8476711 DOI: 10.1007/s10162-021-00811-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 08/02/2021] [Indexed: 12/22/2022] Open
Abstract
Cochlear implants (CIs) are the world's most successful sensory prosthesis and have been the subject of intense research and development in recent decades. We critically review the progress in CI research, and its success in improving patient outcomes, from the turn of the century to the present day. The review focuses on the processing, stimulation, and audiological methods that have been used to try to improve speech perception by human CI listeners, and on fundamental new insights in the response of the auditory system to electrical stimulation. The introduction of directional microphones and of new noise reduction and pre-processing algorithms has produced robust and sometimes substantial improvements. Novel speech-processing algorithms, the use of current-focusing methods, and individualised (patient-by-patient) deactivation of subsets of electrodes have produced more modest improvements. We argue that incremental advances have and will continue to be made, that collectively these may substantially improve patient outcomes, but that the modest size of each individual advance will require greater attention to experimental design and power. We also briefly discuss the potential and limitations of promising technologies that are currently being developed in animal models, and suggest strategies for researchers to collectively maximise the potential of CIs to improve hearing in a wide range of listening situations.
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Affiliation(s)
- Robert P Carlyon
- Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, CB2 7EF, UK.
| | - Tobias Goehring
- Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, CB2 7EF, UK
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Zhou N, Zhu Z, Dong L, Galvin J. Sensitivity to Pulse Phase Duration as a Marker of Neural Health Across Cochlear Implant Recipients and Electrodes. J Assoc Res Otolaryngol 2021; 22:177-192. [PMID: 33559041 PMCID: PMC7943680 DOI: 10.1007/s10162-021-00784-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 01/03/2021] [Indexed: 11/19/2022] Open
Abstract
In cochlear implants, loudness has been shown to grow more slowly with increasing pulse phase duration (PPD) than with pulse amplitude (PA), possibly due to “leaky” charge integration. This leakiness has been recently quantified in terms of “charge integration efficiency,” defined as the log difference between the PPD dynamic range and PA dynamic range (both expressed in charge units), relative to a common threshold anchor. Such leakiness may differ across electrodes and/or test ears, and may reflect underlying neural health. In this study, we examined the across-site variation of charge integration in recipients of Cochlear© devices. PPD and PA dynamic ranges were measured relative to two threshold anchors with either a 25- or 50-microsecond PPD. Strength-duration functions, previously shown to relate to survival of spiral ganglion cells and peripheral processes, were compared to charge integration efficiency on selected electrodes. Results showed no significant or systematic relationship between the across-site variation in charge integration efficiency and electrode position or threshold levels. Charge integration efficiency was poorer with the 50-μs threshold anchor, suggesting that greater leakiness was associated with larger PPD dynamic ranges. Poorer and more variable charge integration efficiency across electrodes was associated with longer duration of any hearing loss, consistent with the idea that poor integration is related to neural degeneration. More variable integration efficiency was also associated with poorer speech recognition performance across test ears. The slopes of the strength-duration functions at maximum acceptable loudness were significantly correlated with charge integration efficiency. However, the strength-duration slopes were not predictive of duration of any hearing loss or speech recognition performance in our participants. As such, charge integration efficiency may be a better candidate to measure leakiness in neural populations across the electrode array, as well as the general health of the auditory nerve in human cochlear implant recipients.
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Affiliation(s)
- Ning Zhou
- Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, 27834, USA
| | - Zhen Zhu
- Department of Engineering, East Carolina University, Greenville, NC, 27834, USA
| | - Lixue Dong
- Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, 27834, USA
| | - John Galvin
- House Ear Institute, 2100 W. Third St., Suite 101, Los Angeles, CA, 90057, USA.
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Ramped pulse shapes are more efficient for cochlear implant stimulation in an animal model. Sci Rep 2020; 10:3288. [PMID: 32094368 PMCID: PMC7039949 DOI: 10.1038/s41598-020-60181-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Accepted: 02/03/2020] [Indexed: 01/20/2023] Open
Abstract
In all commercial cochlear implant (CI) devices, the electric stimulation is performed with a rectangular pulse that generally has two phases of opposite polarity. To date, developing new stimulation strategies has relied on the efficacy of this shape. Here, we investigate the potential of a novel stimulation paradigm that uses biophysically-inspired electrical ramped pulses. Using electrically-evoked auditory brainstem response (eABR) recordings in mice, we found that less charge, but higher current level amplitude, is needed to evoke responses with ramped shapes that are similar in amplitude to responses obtained with rectangular shapes. The most charge-efficient pulse shape had a rising ramp over both phases, supporting findings from previous in vitro studies. This was also true for longer phase durations. Our study presents the first physiological data on CI-stimulation with ramped pulse shapes. By reducing charge consumption ramped pulses have the potential to produce more battery-efficient CIs and may open new perspectives for designing other efficient neural implants in the future.
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Naert G, Pasdelou MP, Le Prell CG. Use of the guinea pig in studies on the development and prevention of acquired sensorineural hearing loss, with an emphasis on noise. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2019; 146:3743. [PMID: 31795705 PMCID: PMC7195866 DOI: 10.1121/1.5132711] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Revised: 07/30/2019] [Accepted: 08/12/2019] [Indexed: 05/10/2023]
Abstract
Guinea pigs have been used in diverse studies to better understand acquired hearing loss induced by noise and ototoxic drugs. The guinea pig has its best hearing at slightly higher frequencies relative to humans, but its hearing is more similar to humans than the rat or mouse. Like other rodents, it is more vulnerable to noise injury than the human or nonhuman primate models. There is a wealth of information on auditory function and vulnerability of the inner ear to diverse insults in the guinea pig. With respect to the assessment of potential otoprotective agents, guinea pigs are also docile animals that are relatively easy to dose via systemic injections or gavage. Of interest, the cochlea and the round window are easily accessible, notably for direct cochlear therapy, as in the chinchilla, making the guinea pig a most relevant and suitable model for hearing. This article reviews the use of the guinea pig in basic auditory research, provides detailed discussion of its use in studies on noise injury and other injuries leading to acquired sensorineural hearing loss, and lists some therapeutics assessed in these laboratory animal models to prevent acquired sensorineural hearing loss.
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Affiliation(s)
| | | | - Colleen G Le Prell
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Dallas, Texas 75080, USA
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Mesnildrey Q, Macherey O, Herzog P, Venail F. Impedance measures for a better understanding of the electrical stimulation of the inner ear. J Neural Eng 2018; 16:016023. [PMID: 30523898 DOI: 10.1088/1741-2552/aaecff] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The performance of cochlear implant (CI) listeners is limited by several factors among which the lack of spatial selectivity of the electrical stimulation. Recently, many studies have explored the use of multipolar strategies where several electrodes are stimulated simultaneously to focus the electrical field in a restricted region of the cochlea. OBJECTIVE These strategies are based on several assumptions concerning the electrical properties of the inner ear that need validation. The first, often implicit, assumption is that the medium is purely resistive and that the current waveforms produced by several electrodes sum linearly. The second assumption relates to the estimation of the contribution of each electrode to the overall electrical field. These individual contributions are usually obtained by stimulating each electrode and measuring the resulting voltage with the other inactive electrodes (i.e. the impedance matrix). However, measuring the voltage on active electrodes (i.e. the diagonal of the matrix) is not straightforward because of the polarization of the electrode-fluid interface. In existing multipolar strategies, the diagonal terms of the matrix are therefore inferred using linear extrapolation from measurements made at neighboring electrodes. APPROACH In experiment 1, several impedance measurements were carried out in vitro and in eight CI users using sinusoidal and pulsatile waveforms to test the resistivity and linearity hypotheses. In experiment 2, we used an equivalent electrical model including a constant phase element in order to isolate the polarization component of the contact impedance. MAIN RESULTS In experiment 1, high-resolution voltage recordings (1.1 MHz sampling) showed the resistivity assumption to be valid at 46.4 kHz, the highest frequency tested. However, these measures also revealed the presence of parasitic capacitive effects at high frequency that could be deleterious to multipolar strategies. Experiment 2 showed that the electrical model provides a better account of the high-resolution impedance measurements than previous approaches in the CI field that used resistor-capacitance circuit models. SIGNIFICANCE These results validate the main hypotheses underlying the use of multipolar stimulation but also suggest possible modifications to their implementation, including the use of an impedance model and the modification of the electrical pulse waveform.
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Affiliation(s)
- Quentin Mesnildrey
- Aix Marseille Univ., CNRS, Centrale Marseille, LMA, 4 impasse Nikola TESLA, CS 40006, F-13453, Marseille Cedex 13, France
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Adenis V, Gourévitch B, Mamelle E, Recugnat M, Stahl P, Gnansia D, Nguyen Y, Edeline JM. ECAP growth function to increasing pulse amplitude or pulse duration demonstrates large inter-animal variability that is reflected in auditory cortex of the guinea pig. PLoS One 2018; 13:e0201771. [PMID: 30071005 PMCID: PMC6072127 DOI: 10.1371/journal.pone.0201771] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Accepted: 07/21/2018] [Indexed: 12/20/2022] Open
Abstract
Despite remarkable advances made to ameliorate how cochlear implants process the acoustic environment, many improvements can still be made. One of most fundamental questions concerns a strategy to simulate an increase in sound intensity. Psychoacoustic studies indicated that acting on either the current, or the duration of the stimulating pulses leads to perception of changes in how loud the sound is. The present study compared the growth function of electrically evoked Compound Action Potentials (eCAP) of the 8th nerve using these two strategies to increase electrical charges (and potentially to increase the sound intensity). Both with chronically (experiment 1) or acutely (experiment 2) implanted guinea pigs, only a few differences were observed between the mean eCAP amplitude growth functions obtained with the two strategies. However, both in chronic and acute experiments, many animals showed larger increases of eCAP amplitude with current increase, whereas some animals showed larger of eCAP amplitude with duration increase, and other animals show no difference between either approaches. This indicates that the parameters allowing the largest increase in eCAP amplitude considerably differ between subjects. In addition, there was a significant correlation between the strength of neuronal firing rate in auditory cortex and the effect of these two strategies on the eCAP amplitude. This suggests that pre-selecting only one strategy for recruiting auditory nerve fibers in a given subject might not be appropriate for all human subjects.
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Affiliation(s)
- Victor Adenis
- Paris-Saclay Institute of Neurosciences (Neuro-PSI) Université Paris-Sud, Orsay, France
- CNRS UMR 9197, Orsay, France
- Université Paris-Saclay, Orsay, France
| | - Boris Gourévitch
- Paris-Saclay Institute of Neurosciences (Neuro-PSI) Université Paris-Sud, Orsay, France
- CNRS UMR 9197, Orsay, France
- Université Paris-Saclay, Orsay, France
| | | | | | | | | | - Yann Nguyen
- INSERM UMR-S-1159, Paris, France
- Université Paris-VI, Paris, France
| | - Jean-Marc Edeline
- Paris-Saclay Institute of Neurosciences (Neuro-PSI) Université Paris-Sud, Orsay, France
- CNRS UMR 9197, Orsay, France
- Université Paris-Saclay, Orsay, France
- * E-mail:
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Zhou N, Dong L. Evaluating Multipulse Integration as a Neural-Health Correlate in Human Cochlear-Implant Users: Relationship to Psychometric Functions for Detection. Trends Hear 2018; 21:2331216517690108. [PMID: 28150534 PMCID: PMC5308440 DOI: 10.1177/2331216517690108] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
In electrical hearing, multipulse integration (MPI) describes the rate at which detection threshold decreases with increasing stimulation rate in a fixed-duration pulse train. In human subjects, MPI has been shown to be dependent on the psychophysically estimated spread of neural excitation at a high stimulation rate, with broader spread predicting greater integration. The first aim of the present study was to replicate this finding using alternative methods for measuring MPI and spread of neural excitation. The second aim was to test the hypothesis that MPI is related to the slope of the psychometric function for detection. Specifically, a steep d' versus stimulus level function would predict shallow MPI since the amount of current reduction necessary to compensate for an increase in stimulation rate to maintain threshold would be small. The MPI function was measured by obtaining adaptive detection thresholds at 160 and 640 pulses per second. Spread of neural excitation was measured by forward-masked psychophysical tuning curves. All psychophysical testing was performed in a monopolar stimulation mode (MP 1 + 2). Results showed that MPI was correlated with the slopes of the tuning curves, with broader tuning predicting steeper MPI, confirming the earlier finding. However, there was no relationship between MPI and the slopes of the psychometric functions. These results suggest that a broad stimulation of the cochlea facilitates MPI. MPI however is not related to the estimated neural excitation growth with current level near the behavioral threshold, at least in monopolar stimulation.
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Affiliation(s)
- Ning Zhou
- 1 Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, USA
| | - Lixue Dong
- 1 Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, USA
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Hayashida Y, Umehira Y, Takatani K, Futami S, Kameda S, Kamata T, Khan AU, Takeuchi Y, Imai M, Yagi T. Cortical neural excitations in rats in vivo with using a prototype of a wireless multi-channel microstimulation system. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:1642-5. [PMID: 26736590 DOI: 10.1109/embc.2015.7318690] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Understanding neural responses to multi-site electrical stimuli would be of essential importance for developing cortical neural prostheses. In order to provide a tool for such studies in experimental animals, we recently constructed a prototype of a wireless multi-channel microstimulation system, consisting of a stimulator chip, wireless data/power transmitters and receivers, and microcomputers. The proper operations of the system in cortical neural excitations were examined in anesthetized rats in vivo, with utilizing the voltage-sensitive dye imaging technique.
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11
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Chatterjee M, Kulkarni AM. Sensitivity to pulse phase duration in cochlear implant listeners: effects of stimulation mode. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2014; 136:829-40. [PMID: 25096116 PMCID: PMC4144184 DOI: 10.1121/1.4884773] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Revised: 06/09/2014] [Accepted: 06/11/2014] [Indexed: 05/23/2023]
Abstract
The objective of this study was to investigate charge-integration at threshold by cochlear implant listeners using pulse train stimuli in different stimulation modes (monopolar, bipolar, tripolar). The results partially confirmed and extended the findings of previous studies conducted in animal models showing that charge-integration depends on the stimulation mode. The primary overall finding was that threshold vs pulse phase duration functions had steeper slopes in monopolar mode and shallower slopes in more spatially restricted modes. While the result was clear-cut in eight users of the Cochlear Corporation(TM) device, the findings with the six user of the Advanced Bionics(TM) device who participated were less consistent. It is likely that different stimulation modes excite different neuronal populations and/or sites of excitation on the same neuron (e.g., peripheral process vs central axon). These differences may influence not only charge integration but possibly also temporal dynamics at suprathreshold levels and with more speech-relevant stimuli. Given the present interest in focused stimulation modes, these results have implications for cochlear implant speech processor design and protocols used to map acoustic amplitude to electric stimulation parameters.
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Affiliation(s)
- Monita Chatterjee
- Boys Town National Research Hospital, 555 N 30th Street, Omaha, Nebraska 68131
| | - Aditya M Kulkarni
- Boys Town National Research Hospital, 555 N 30th Street, Omaha, Nebraska 68131
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12
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Ramekers D, Versnel H, Strahl SB, Smeets EM, Klis SFL, Grolman W. Auditory-nerve responses to varied inter-phase gap and phase duration of the electric pulse stimulus as predictors for neuronal degeneration. J Assoc Res Otolaryngol 2014; 15:187-202. [PMID: 24469861 DOI: 10.1007/s10162-013-0440-x] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Accepted: 12/26/2013] [Indexed: 12/17/2022] Open
Abstract
After severe hair cell loss, secondary degeneration of spiral ganglion cells (SGCs) is observed-a gradual process that spans years in humans but only takes weeks in guinea pigs. Being the target for cochlear implants (CIs), the physiological state of the SGCs is important for the effectiveness of a CI. For assessment of the nerve's state, focus has generally been on its response threshold. Our goal was to add a more detailed characterization of SGC functionality. To this end, the electrically evoked compound action potential (eCAP) was recorded in normal-hearing guinea pigs and guinea pigs that were deafened 2 or 6 weeks prior to the experiments. We evaluated changes in eCAP characteristics when the phase duration (PD) and inter-phase gap (IPG) of a biphasic current pulse were varied. We correlated the magnitude of these changes to quantified histological measures of neurodegeneration (SGC packing density and SGC size). The maximum eCAP amplitude, derived from the input-output function, decreased after deafening, and increased with both PD and IPG. The eCAP threshold did not change after deafening, and decreased with increasing PD and IPG. The dynamic range was wider for the 6-weeks-deaf animals than for the other two groups. Excitability increased with IPG (steeper slope of the input-output function and lower stimulation level at the half-maximum eCAP amplitude), but to a lesser extent for the deafened animals than for normal-hearing controls. The latency was shorter for the 6-weeks-deaf animals than for the other two groups. For several of these eCAP characteristics, the effect size of IPG correlated well with histological measures of degeneration, whereas effect size of PD did not. These correlations depend on the use of high current levels, which could limit clinical application. Nevertheless, their potential of these correlations towards assessment of the condition of the auditory nerve may be of great benefit to clinical diagnostics and prognosis in cochlear implant recipients.
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Affiliation(s)
- Dyan Ramekers
- Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands,
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13
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The polarity sensitivity of the electrically stimulated human auditory nerve measured at the level of the brainstem. J Assoc Res Otolaryngol 2013; 14:359-77. [PMID: 23479187 DOI: 10.1007/s10162-013-0377-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 01/31/2013] [Indexed: 10/27/2022] Open
Abstract
Recent behavioral studies have suggested that the human auditory nerve of cochlear implant (CI) users is mainly excited by the positive (anodic) polarity. Those findings were only obtained using asymmetric pseudomonophasic (PS) pulses where the effect of one phase was measured in the presence of a counteracting phase of opposite polarity, longer duration, and lower amplitude than the former phase. It was assumed that only the short high-amplitude phase was responsible for the excitation. Similarly, it has been shown that electrically evoked compound action potentials could only be obtained in response to the anodic phases of asymmetric pulses. Here, experiment 1 measured electrically evoked auditory brainstem responses to standard symmetric, PS, reversed pseudomonophasic, and reversed pseudomonophasic with inter-phase gap (6 ms) pulses presented for both polarities. Responses were time locked to the short high-amplitude phase of asymmetric pulses and were smaller, but still measurable, when that phase was cathodic than when it was anodic. This provides the first evidence that cathodic stimulation can excite the auditory system of human CI listeners and confirms that this stimulation is nevertheless less effective than for the anodic polarity. A second experiment studied the polarity sensitivity at different intensities by means of a loudness balancing task between pseudomonophasic anodic (PSA) and pseudomonophasic cathodic (PSC) stimuli. Previous studies had demonstrated greater sensitivity to anodic stimulation only for stimuli producing loud percepts. The results showed that PSC stimuli required higher amplitudes than PSA stimuli to reach the same loudness and that this held for current levels ranging from 10 to 100% of the dynamic range.
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Ahn JH, Oh SH, Chung JW, Lee KS. Facial nerve stimulation after cochlear implantation according to types of Nucleus 24-channel electrode arrays. Acta Otolaryngol 2009; 129:588-91. [PMID: 18720074 DOI: 10.1080/00016480802325965] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
CONCLUSION In this study, we concluded that electrode design and location did not have a high level of influence on the prevalence of facial nerve stimulation (FNS) in normal cochleae. OBJECTIVE To analysis the prevalence of FNS after cochlear implantation with Nucleus 24-channel devices according to types of electrodes arrays. PATIENTS AND METHODS We retrospectively analyzed medical and mapping records of 394 patients who received cochlear implants (CIs) manufactured by Cochlear Corporation from April 1999 to March 2007. RESULTS In all, 23 of 394 (5.8%) patients had FNS (CI24M 4 of 39 [10.3%], CI24RCS 9 of 192 [4.7%], CI24RST 9 of 21 [42.9%], and CI24RECA 1 of 87 [1.1%]). In addition, 4 of 324 (1.2%) patients with normal cochleae complained of FNS (CI24M 1 of 33 [3.0%], CI24RCS 2 of 173 [1.2%], and CI24RECA 1 of 71 [1.4%]). There was no difference between straight and perimodiolar electrode arrays in patients with normal cochleae. In addition, when comparing two types of Contour electrodes, Contour Advance (soft-tip) electrodes offered significantly lower incidence of FNS than Contour electrode arrays. We could manage these patients with methods such as decrease of C-level, selective channel turning off, and changes of mapping strategies.
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Pfingst BE, Burkholder-Juhasz RA, Xu L, Thompson CS. Across-site patterns of modulation detection in listeners with cochlear implants. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2008; 123:1054-62. [PMID: 18247907 PMCID: PMC2431465 DOI: 10.1121/1.2828051] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
In modern cochlear implants, much of the information required for recognition of important sounds is conveyed by temporal modulation of the charge per phase in interleaved trains of electrical pulses. In this study, modulation detection thresholds (MDTs) were used to assess listeners' abilities to detect sinusoidal modulation of charge per phase at each available stimulation site in their 22-electrode implants. Fourteen subjects were tested. MDTs were found to be highly variable across stimulation sites in most listeners. The across-site patterns of MDTs differed considerably from subject to subject. The subject-specific patterns of across-site variability of MDTs suggest that peripheral site-specific characteristics, such as electrode placement and the number and condition of surviving neurons, play a primary role in determining modulation sensitivity. Across-site patterns of detection thresholds (T levels), maximum comfortable loudness levels (C levels) and dynamic ranges (DRs) were not consistently correlated with across-site patterns of MDTs within subjects, indicating that the mechanisms underlying across-site variation in these measures differed from those underlying across-site variation in MDTs. MDTs sampled from multiple sites in a listener's electrode array might be useful for diagnosing across-subject differences in speech recognition with cochlear implants and for guiding strategies to improve the individual's perception.
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Affiliation(s)
- Bryan E Pfingst
- Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan, Ann Arbor, Michigan 48109-5616, USA.
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16
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Izzo AD, Suh E, Pathria J, Walsh JT, Whitlon DS, Richter CP. Selectivity of neural stimulation in the auditory system: a comparison of optic and electric stimuli. JOURNAL OF BIOMEDICAL OPTICS 2007; 12:021008. [PMID: 17477715 DOI: 10.1117/1.2714296] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Pulsed, mid-infrared lasers were recently investigated as a method to stimulate neural activity. There are significant benefits of optically stimulating nerves over electrically stimulating, in particular the application of more spatially confined neural stimulation. We report results from experiments in which the gerbil auditory system was stimulated by optical radiation, acoustic tones, or electric current. Immunohistochemical staining for the protein c-FOS revealed the spread of excitation. We demonstrate a spatially selective activation of neurons using a laser; only neurons in the direct optical path are stimulated. This pattern of c-FOS labeling is in contrast to that after electrical stimulation. Electrical stimulation leads to a large, more spatially extended population of labeled, activated neurons. In the auditory system, optical stimulation of nerves could have a significant impact on the performance of cochlear implants, which can be limited by the electric current spread.
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Affiliation(s)
- Agnella D Izzo
- Northwestern University, Biomedical Engineering, 2145 Sheridan Road, Tech E310, Evanston, Illinois 60208, USA
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17
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Macherey O, Carlyon RP, van Wieringen A, Wouters J. A dual-process integrator-resonator model of the electrically stimulated human auditory nerve. J Assoc Res Otolaryngol 2007; 8:84-104. [PMID: 17221144 PMCID: PMC2538421 DOI: 10.1007/s10162-006-0066-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Accepted: 11/03/2006] [Indexed: 11/28/2022] Open
Abstract
A phenomenological dual-process model of the electrically stimulated human auditory nerve is presented and compared to threshold and loudness data from cochlear implant users. The auditory nerve is modeled as two parallel processes derived from linearized equations of conductance-based models. The first process is an integrator, which dominates stimulation for short-phase duration biphasic pulses and high-frequency sinusoidal stimuli. It has a relatively short time constant (0.094 ms) arising from the passive properties of the membrane. The second process is a resonator, which induces nonmonotonic functions of threshold vs frequency with minima around 80 Hz. The ion channel responsible for this trend has a relatively large relaxation time constant of about 1 ms. Membrane noise is modeled as a Gaussian noise, and loudness sensation is assumed to relate to the probability of firing of a neuron during a 20-ms rectangular window. Experimental psychophysical results obtained in seven previously published studies can be interpreted with this model. The model also provides a physiologically based account of the nonmonotonic threshold vs frequency functions observed in biphasic and sinusoidal stimulation, the large threshold decrease obtained with biphasic pulses having a relatively long inter-phase gap and the effects of asymmetric pulses.
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Affiliation(s)
- Olivier Macherey
- ExpORL, Department of Neurosciences, Katholieke Universiteit Leuven, Herestraat 49 bus 721, 3000, Leuven, Belgium.
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18
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Le Prell CG, Kawamoto K, Raphael Y, Dolan DF. Electromotile hearing: acoustic tones mask psychophysical response to high-frequency electrical stimulation of intact guinea pig cochleae. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2006; 120:3889-900. [PMID: 17225416 PMCID: PMC3132799 DOI: 10.1121/1.2359238] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
When sinusoidal electric stimulation is applied to the intact cochlea, a frequency-specific acoustic emission can be recorded in the ear canal. Acoustic emissions are produced by basilar membrane motion, and have been used to suggest a corresponding acoustic sensation termed "electromotile hearing." Electromotile hearing has been specifically attributed to electric stimulation of outer hair cells in the intact organ of Corti. To determine the nature of the auditory perception produced by electric stimulation of a cochlea with intact outer hair cells, guinea pigs were tested in a psychophysical task. First, subjects were trained to report detection of sinusoidal acoustic stimuli and dynamic range was assessed using response latency. Subjects were then implanted with a ball electrode placed into scala tympani. Following the surgical implant procedure, subjects were transferred to a task in which acoustic signals were replaced by sinusoidal electric stimulation, and dynamic range was assessed again. Finally, the ability of acoustic pure-tone stimuli to mask the detection of the electric signals was assessed. Based on the masking effects, it is concluded that sinusoidal electric stimulation of the intact cochlea results in perception of a tonal (rather than a broadband or noisy) sound at a frequency of 8 kHz or above.
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Affiliation(s)
- Colleen G Le Prell
- Kresge Hearing Research Institute, 1301 East Ann Street, Ann Arbor, Michigan 48109-0506, USA.
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19
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Prado-Guitierrez P, Fewster LM, Heasman JM, McKay CM, Shepherd RK. Effect of interphase gap and pulse duration on electrically evoked potentials is correlated with auditory nerve survival. Hear Res 2006; 215:47-55. [PMID: 16644157 PMCID: PMC1831823 DOI: 10.1016/j.heares.2006.03.006] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Accepted: 03/07/2006] [Indexed: 11/25/2022]
Abstract
We investigated the effect of pulse duration (PD) and interphase-gap (IPG) on the electrically-evoked auditory brain stem response (EABR) and viiith nerve compound action potential (ECAP) of deafened guinea pigs in order to test the hypothesis that the extent of change in these neural responses is affected by the histological status of the auditory nerve. Fifteen guinea pigs were deafened by co-administration of kanamycin and furosemide. Animals were acutely implanted with an 8-band electrode array at 1, 4 or 12 weeks following deafening. EABR and ECAP input/output functions were recorded in response to charge balanced biphasic current pulses. We determined the change in current required to equalize; (i) the EABR amplitude when the duration of the current pulse was doubled (104-208 micros/phase); and (ii) the EABR and ECAP amplitudes when the IPG was increased from 8 to 58 micros using a 104 micros/phase current pulse. Following the completion of each experiment the cochleae were examined quantitatively for spiral ganglion neuron survival. As expected, the current level required to evoke an EABR with equal amplitude was lower when the animal was stimulated with current pulses of 208 compared with 104 micros/phase. Moreover, the current level required to evoke EABR/ECAPs with equal amplitude was lower when current pulses had an IPG of 58 versus 8 micros. Importantly, there was a reduction in the magnitude of this effect with greater neural loss; the reduced efficacy of changing both PD and IPG on these electrically-evoked potentials was statistically correlated with neural survival. These results may provide a tool for investigating the contribution of auditory nerve survival to clinical performance among cochlear implant subjects.
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20
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Hughes ML, Abbas PJ. Electrophysiologic channel interaction, electrode pitch ranking, and behavioral threshold in straight versus perimodiolar cochlear implant electrode arrays. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2006; 119:1538-47. [PMID: 16583899 DOI: 10.1121/1.2164969] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The primary goal of this study was to examine electrophysiologic measures of channel interaction, electrode pitch discrimination ability using a pitch-ranking task, and behavioral threshold levels in individuals implanted with a straight electrode array versus a perimodiolar array. It was hypothesized that perimodiolar arrays should yield lower thresholds, less channel interaction as measured with the electrically evoked compound action potential (ECAP), and better electrode pitch-ranking ability. Results from ten adult Nucleus 24 recipients (N=5 straight array, N=5 perimodiolar Contour array) showed no significant difference in threshold between the two electrode designs; however, there was significantly better electrode pitch-ranking ability and less channel interaction as measured with the ECAP for perimodiolar electrodes. Additionally, there was a significant positive correlation between behavioral threshold and width of the ECAP interaction function for Contour group data. There was no significant correlation between behavioral threshold and electrode pitch-ranking ability. These data suggest that electrode design and/or perimodiolar position may reduce physiologic channel interaction in the cochlea and improve electrode pitch discrimination ability; however, this positive finding did not translate into significantly better speech perception ability for Contour subjects.
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Affiliation(s)
- Michelle L Hughes
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242, USA.
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21
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Chatterjee M, Oba SI. Noise improves modulation detection by cochlear implant listeners at moderate carrier levels. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2005; 118:993-1002. [PMID: 16158655 DOI: 10.1121/1.1929258] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Envelope detection and processing are very important for cochlear implant (CI) listeners, who must rely on obtaining significant amounts of acoustic information from the time-varying envelopes of stimuli. In previous work, Chatterjee and Robert [JARO 2(2), 159-171 (2001)] reported on a stochastic-resonance-type effect in modulation detection by CI listeners: optimum levels of noise in the envelope enhanced modulation detection under certain conditions, particularly when the carrier level was low. The results of that study suggested that a low carrier level was sufficient to evoke the observed stochastic resonance effect, but did not clarify whether a low carrier level was necessary to evoke the effect. Modulation thresholds in CI listeners generally decrease with increasing carrier level. The experiments in this study were designed to investigate whether the observed noise-induced enhancement is related to the low carrier level per se, or to the poor modulation sensitivity that accompanies it. This was done by keeping the carrier amplitude fixed at a moderate level and increasing modulation frequency so that modulation sensitivity could be reduced without lowering carrier level. The results suggest that modulation sensitivity, not carrier level, is the primary factor determining the effect of the noise.
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Affiliation(s)
- Monita Chatterjee
- Department of Auditory Implants and Perception, House Ear Institute, 2100 W. Third Street, Los Angeles, California 90057, USA.
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22
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van Wieringen A, Carlyon RP, Laneau J, Wouters J. Effects of waveform shape on human sensitivity to electrical stimulation of the inner ear. Hear Res 2005; 200:73-86. [PMID: 15668040 DOI: 10.1016/j.heares.2004.08.006] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2004] [Accepted: 08/05/2004] [Indexed: 11/23/2022]
Abstract
Psychophysical measures of the electrically stimulated human auditory system were obtained for different types of symmetric and asymmetric charge-balanced waveforms. Absolute detection thresholds of biphasic, pseudomonophasic, and 'alternating monophasic' current waveforms delivered by a bipolar intra-cochlear electrode pair were determined for four subjects implanted with the LAURA device. Thresholds for alternating monophasic stimuli, in which anodic and cathodic phases alternated every 5 ms, were 5-8 dB lower than for the biphasic waveforms for all four subjects. For two of the four subjects, thresholds for the pseudomonophasic waveforms were also significantly lower than for the biphasic waveforms. These pseudomonophasic thresholds were greatly affected neither by a 500-micros gap inserted between the two phases, nor by whether the shorter phase preceded or followed the longer one. Loudness balancing measures performed at the most comfortable levels also showed that, for equal loudness, alternating monophasic stimuli required a lower level than biphasic and pseudomonophasic waveforms. For three of the four subjects, the dynamic ranges of the pseudomonophasic (but not alternating monophasic) waveforms were greater than those of the biphasic waveforms. The results demonstrate that thresholds and dynamic ranges of human cochlear implant users can be controlled by manipulating the way in which the charge produced by the initial phase of an electrical pulse is recovered.
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23
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Carlyon RP, van Wieringen A, Deeks JM, Long CJ, Lyzenga J, Wouters J. Effect of inter-phase gap on the sensitivity of cochlear implant users to electrical stimulation. Hear Res 2005; 205:210-24. [PMID: 15953530 DOI: 10.1016/j.heares.2005.03.021] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2004] [Accepted: 03/22/2005] [Indexed: 11/24/2022]
Abstract
Human behavioral thresholds for trains of biphasic pulses applied to a single channel of Nucleus CI24 and LAURA cochlear implants were measured as a function of inter-phase gap (IPG). Experiment 1 used bipolar stimulation, a 100-pps pulse rate, and a 400-ms stimulus duration. In one condition, the two phases of each pulse had opposite polarity. Thresholds continued to drop by 9-10 dB as IPG was increased from near zero to the longest value tested (2900 micros for CI24, 4900 micros for LAURA). This time course is much longer than reported for single-cell recordings from animals. In a second condition, the two phases of each pulse had the same polarity, which alternated from pulse to pulse. Thresholds were independent of IPG, and similar to those in condition 1 at IPG=4900 micros. Experiment 2 used monopolar stimulation. One condition was similar to condition 1 of experiment 1, and thresholds also dropped up to the longest IPG studied (2900 micros). This also happened when the pulse rate was reduced to 20 pps, and when only a single pulse was presented on each trial. Keeping IPG constant at 8 micros and adding an extra biphasic pulse x ms into each period produced thresholds that were roughly independent of x, indicating that the effect of IPG in the other conditions was not due to a release from refractoriness at sites central to the auditory nerve. Experiment 3 measured thresholds at three IPGs, which were less than, equal to, and more than one half of the interval between successive pulses. Thresholds were lowest at the intermediate IPG. The results of all experiments could be fit by a linear model consisting of a lowpass filter based on the function relating threshold to the frequency of sinusoidal electrical stimulation. The data and model have implications for reducing the power consumption of cochlear implants.
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Affiliation(s)
- Robert P Carlyon
- MRC Cognition and Brain Sciences Unit, 15 Chaucer Rd., Cambridge CB2 2EF, England, UK.
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24
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Chen H, Ishihara YC, Zeng FG. Pitch discrimination of patterned electric stimulation. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2005; 118:338-45. [PMID: 16119354 DOI: 10.1121/1.1937228] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
One reason for the poor pitch performance in current cochlear-implant users may be the highly synchronized neural firing in electric hearing that lacks stochastic properties of neural firing in normal acoustic hearing. This study used three different electric stimulation patterns, jittered, probabilistic, and auditory-model-generated pulses, to mimic some aspects of the normal neural firing pattern in acoustic hearing. Pitch discrimination was measured at standard frequencies of 100, 250, 500, and 1000 Hz on three Nucleus-24 cochlear-implant users. To test the utility of the autocorrelation pitch perception model in electric hearing, one, two, and four electrodes were stimulated independently with the same patterned electric stimulation. Results showed no improvement in performance with any experimental pattern compared to the fixed-rate control. Pitch discrimination was actually worsened with the jittered pattern at low frequencies (125 and 250 Hz) than that of the control, suggesting that externally introduced stochastic properties do not improve pitch perception in electric stimulation. The multiple-electrode stimulation did not improve performance but did not degrade performance either. The present results suggest that both "the right time and the right place" may be needed to restore normal pitch perception in cochlear-implant users.
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Affiliation(s)
- Hongbin Chen
- Hearing and Speech Research Laboratory, Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, USA.
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25
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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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26
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Abstract
The dramatic differences observed when comparing auditory neural responses to electrical and acoustic stimulation may illustrate one of the important mechanisms underlying the sometimes poor speech recognition abilities of individuals with cochlear implants. Recent research has suggested that the absence of a stochastic component in neural responses to electrical activation may be an important potential mechanism for this degradation in speech recognition performance. There are few psychophysical data, however, demonstrating that this stochastic behavior can be measured directly in implant subjects. In this study, variability in psychophysical threshold was investigated as a measure of the stochastic nature of the underlying neural response in human and non-human subjects implanted with intracochlear electrode arrays. Threshold data collected in both monopolar and bipolar stimulation modes at several phase durations from cat and human subjects are presented. The nature of the neural input/output curve suggests that threshold variability should increase as the slope of the input/output curve is decreased, i.e. as phase duration is increased. These predictions are confirmed by the pattern of psychophysical results measured experimentally in cat and human subjects. Furthermore, the data may suggest that subjects with higher threshold variability, i.e. a relatively greater stochastic component, are more likely to have higher speech recognition scores.
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Affiliation(s)
- William D Ferguson
- Department of Electrical and Computer Engineering, Box 90291, Duke University, Durham, NC 27708-0291, USA
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27
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Bierer JA, Middlebrooks JC. Auditory cortical images of cochlear-implant stimuli: dependence on electrode configuration. J Neurophysiol 2002; 87:478-92. [PMID: 11784764 DOI: 10.1152/jn.00212.2001] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study examines patterns of auditory cortical activity elicited by single-pulse cochlear implant stimuli that vary in electrode configuration, cochlear place of stimulation, and stimulus level. Recordings were made from the primary auditory cortex (area A1) of ketamine-anesthetized guinea pigs. The spatiotemporal pattern of neural spike activity was measured simultaneously across 16 cortical locations spanning approximately 2-3 octaves of the tonotopic axis. Such a pattern, averaged over 40 presentations of any particular stimulus, was defined as the "cortical image" of that stimulus. Acutely deafened guinea pigs were implanted with a 6-electrode animal version of the 22-electrode Nucleus banded electrode array (Cochlear). Cochlear electrode configurations consisted of monopolar (MP), bipolar (BP + N) with N inactive electrodes between the active and return electrodes (0 < or = N < or = 4), tripolar (TP) with one active electrode and two flanking return electrodes, and common ground (CG) with one active electrode and as many as five return electrodes. Cortical images typically showed a focus of maximum spike probability and minimum latency. Spike probabilities tended to decrease, and latencies tended to increase, with increasing cortical distance from that focus. Cortical images of TP stimuli were the most spatially compact, followed by BP + N images, and then MP images, which were the broadest. Images of CG stimuli were rather variable across animals and stimulus channels. The locations of cortical images shifted systematically from caudal to rostral as the cochlear place of stimulation changed from basal to apical. At the most sensitive cortical site for each condition, the dynamic ranges over which spike rates increased with increased current level were restricted to about 1-2 dB, regardless of configuration. Dynamic ranges tended to increase with increasing cortical distance from the most sensitive site. Electrode configurations that produced compact cortical images (e.g., TP and BP + 0) showed the greatest range of thresholds within each cortical image and the largest dynamic range at cortical sites removed from the most sensitive site.
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Affiliation(s)
- Julie Arenberg Bierer
- Kresge Hearing Research Institute (Department of Otorhinolaryngology) and Neuroscience Program, University of Michigan, Ann Arbor, Michigan 48109-0506, USA
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28
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Frijns JH, Briaire JJ, Grote JJ. The Importance of Human Cochlear Anatomy for the Results of Modiolus-Hugging Multichannel Cochlear Implants. Otol Neurotol 2001; 22:340-9. [PMID: 11347637 DOI: 10.1097/00129492-200105000-00012] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
HYPOTHESIS The fact that the anatomy of the basal turn of the human cochlea, especially, is essentially different from that of other species is likely to influence the outcome of cochlear implantation. BACKGROUND Multichannel cochlear implants give better speech understanding than single-channel devices. They are intended to make use of the tonotopic organization of the cochlea by selectively stimulating subpopulations of the auditory nerve. At higher stimulus levels and with monopolar stimulation, excitation of nerve fibers from other turns may interfere with this concept, especially with modiolus-hugging electrodes. METHODS A three-dimensional spiraling computer model of the human cochlea, based on histologic data, was used to test the spatial selectivity and the dynamic range before cross-turn stimulation takes place for the Clarion HiFocus implant with and without a positioner. The results were compared with a similar model of the guinea pig cochlea. RESULTS In humans (in contrast to the guinea pig), a well-designed modiolus-hugging electrode yielded reduced current thresholds and high spatial selectivity without reduction of the useful dynamic range. The apical turn of the human cochlea, however, is largely comparable in this respect with the guinea pig cochlea, where cross-turn stimulation reduces the dynamic range substantially. CONCLUSION The clinical success of cochlear implantation in humans and the favorable results with modiolus-hugging devices depend on the anatomy of the human cochlea.
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Affiliation(s)
- J H Frijns
- Ear, Nose, and Throat Department, Leiden University Medical Center, The Netherlands
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Abstract
For almost 10 years, chronic stimulation has been known to affect spiral ganglion cell (SGC) survival in the deaf ear. However, the reported effects of chronic stimulation vary across preparations and studies. In this review, the effects of chronic stimulation on the deafened auditory periphery are examined, and variables that may impact on the efficacy of chronic stimulation are identified. The effects of deafening on the unstimulated peripheral and central auditory system are also described, as the deafened, unstimulated system is the canvas upon which stimulation-mediated effects are imposed. Discrepancies in the effects of chronic stimulation across studies may be attributable in large part to the combined effects of the deafening method and the post-deafening delay prior to chronic stimulation, which vary across studies. Emphasis is placed on the need to consider the natural progression of SGC loss following deafening in the absence of chronic stimulation, as the rate of SGC loss almost certainly affects both the efficacy of stimulation, and the impact of any delay between deafening and initiation of stimulation. The differences across preparations complicate direct comparison of protective efficacy of stimulation. At the same time, these differences can be used to our advantage, aiding characterization of the effects of different factors on the efficacy of chronic stimulation as a neuroprotective intervention.
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Affiliation(s)
- A L Miller
- Kresge Hearing Research Institute, 1301 E. Ann Street, Ann Arbor, MI 48109-0506, USA.
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