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Changes in the Electrically Evoked Compound Action Potential over time After Implantation and Subsequent Deafening in Guinea Pigs. J Assoc Res Otolaryngol 2022; 23:721-738. [PMID: 35948695 PMCID: PMC9789241 DOI: 10.1007/s10162-022-00864-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 07/12/2022] [Indexed: 01/06/2023] Open
Abstract
The electrically evoked compound action potential (eCAP) is a direct measure of the responsiveness of the auditory nerve to electrical stimulation from a cochlear implant (CI). CIs offer a unique opportunity to study the auditory nerve's electrophysiological behavior in individual human subjects over time. In order to understand exactly how the eCAP relates to the condition of the auditory nerve, it is crucial to compare changes in the eCAP over time in a controlled model of deafness-induced auditory nerve degeneration. In the present study, 10 normal-hearing young adult guinea pigs were implanted and deafened 4 weeks later, so that the effect of deafening could be monitored within-subject over time. Following implantation, but before deafening, most examined eCAP characteristics significantly changed, suggesting increasing excitation efficacy (e.g., higher maximum amplitude, lower threshold, shorter latency). Conversely, inter-phase gap (IPG) effects on these measures - within-subject difference measures that have been shown to correlate well with auditory nerve survival - did not vary for most eCAP characteristics. After deafening, we observed an initial increase in excitability (steeper slope of the eCAP amplitude growth function (AGF), lower threshold, shorter latency and peak width) which typically returned to normal-hearing levels within a week, after which a slower process, probably reflecting spiral ganglion cell loss, took place over the remaining 6 weeks (e.g., decrease in maximum amplitude, AGF slope, peak area, and IPG effect for AGF slope; increase in IPG effect for latency). Our results suggest that gradual changes in peak width and latency reflect the rate of neural degeneration, while peak area, maximum amplitude, and AGF slope reflect neural population size, which may be valuable for clinical diagnostics.
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Berninger E, Drott M, Romanitan M, Tranebjærg L, Hellström S. Congenital Nonprofound Bilateral Sensorineural Hearing Loss in Children: Comprehensive Characterization of Auditory Function and Hearing Aid Benefit. Audiol Res 2022; 12:539-563. [PMID: 36285911 PMCID: PMC9598400 DOI: 10.3390/audiolres12050054] [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: 08/26/2022] [Revised: 09/28/2022] [Accepted: 10/02/2022] [Indexed: 11/25/2022] Open
Abstract
A prospective cross-sectional design was used to characterize congenital bilateral sensorineural hearing loss (SNHL). The underlying material of >30,000 consecutively screened newborns comprised 11 subjects with nonprofound, alleged nonsyndromic, SNHL. Comprehensive audiological testing was performed at ≈11 years of age. Results showed symmetrical sigmoid-like median pure-tone thresholds (PTTs) reaching 50−60 dB HL. The congenital SNHL revealed recruitment, increased upward spread of masking, distortion product otoacoustic emission (DPOAE) dependent on PTT (≤60 dB HL), reduced auditory brainstem response (ABR) amplitude, and normal magnetic resonance imaging. Unaided recognition of speech in spatially separate competing speech (SCS) deteriorated with increasing uncomfortable loudness level (UCL), plausibly linked to reduced afferent signals. Most subjects demonstrated hearing aid (HA) benefit in a demanding laboratory listening situation. Questionnaires revealed HA benefit in real-world listening situations. This functional characterization should be important for the outline of clinical guidelines. The distinct relationship between DPOAE and PTT, up to the theoretical limit of cochlear amplification, and the low ABR amplitude remain to be elucidated. The significant relation between UCL and SCS has implications for HA-fitting. The fitting of HAs based on causes, mechanisms, and functional characterization of the SNHL may be an individualized intervention approach and deserves future research.
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Affiliation(s)
- Erik Berninger
- Department of Clinical Science, Intervention and Technology, Division of Ear, Nose and Throat Diseases, Karolinska Institutet, 171 77 Stockholm, Sweden
- Department of Audiology and Neurotology, Karolinska University Hospital, 141 86 Stockholm, Sweden
- Correspondence: or
| | - Maria Drott
- Department of Clinical Science, Intervention and Technology, Division of Ear, Nose and Throat Diseases, Karolinska Institutet, 171 77 Stockholm, Sweden
- Department of Audiology and Neurotology, Karolinska University Hospital, 141 86 Stockholm, Sweden
| | - Mircea Romanitan
- Department of Clinical Science, Intervention and Technology, Division of Ear, Nose and Throat Diseases, Karolinska Institutet, 171 77 Stockholm, Sweden
- Department of Audiology and Neurotology, Karolinska University Hospital, 141 86 Stockholm, Sweden
| | - Lisbeth Tranebjærg
- Department of Clinical Genetics, The University Hospital Rigshospital/The Kennedy Centre, DK-2600 Copenhagen, Denmark
- Institute of Clinical Medicine, University of Copenhagen, DK-1165 Copenhagen, Denmark
| | - Sten Hellström
- Department of Clinical Science, Intervention and Technology, Division of Ear, Nose and Throat Diseases, Karolinska Institutet, 171 77 Stockholm, Sweden
- Department of Audiology and Neurotology, Karolinska University Hospital, 141 86 Stockholm, Sweden
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Jahn KN, Arenberg JG. Electrophysiological Estimates of the Electrode-Neuron Interface Differ Between Younger and Older Listeners With Cochlear Implants. Ear Hear 2021; 41:948-960. [PMID: 32032228 PMCID: PMC10424265 DOI: 10.1097/aud.0000000000000827] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES The primary objective of this study was to quantify differences in evoked potential correlates of spiral ganglion neuron (SGN) density between younger and older individuals with cochlear implants (CIs) using the electrically evoked compound action potential (ECAP). In human temporal bone studies and in animal models, SGN density is the lowest in older subjects and in those who experienced long durations of deafness during life. SGN density also varies as a function of age at implantation and hearing loss etiology. Taken together, it is likely that younger listeners who were deafened and implanted during childhood have denser populations of SGNs than older individuals who were deafened and implanted later in life. In animals, ECAP amplitudes, amplitude growth function (AGF) slopes, and their sensitivity to stimulus interphase gap (IPG) are predictive of SGN density. The authors hypothesized that younger listeners who were deafened and implanted as children would demonstrate larger ECAP amplitudes, steeper AGF slopes, and greater IPG sensitivity than older, adult-deafened and implanted listeners. DESIGN Data were obtained from 22 implanted ears (18 individuals). Thirteen ears (9 individuals) were deafened and implanted as children (child-implanted group), and nine ears (9 individuals) were deafened and implanted as adults (adult-implanted group). The groups differed significantly on a number of demographic variables that are implicitly related to SGN density: (1) chronological age; (2) age at implantation; and (3) duration of preimplantation hearing loss. ECAP amplitudes, AGF linear slopes, and thresholds were assessed on a subset of electrodes in each ear in response to two IPGs (7 and 30 µsec). Speech recognition was assessed using a medial vowel identification task. RESULTS Compared with the adult-implanted listeners, individuals in the child-implanted group demonstrated larger changes in ECAP amplitude when the IPG of the stimulus was increased from 7 to 30 µsec (i.e., greater IPG sensitivity). On average, child-implanted participants also had larger ECAP amplitudes and steeper AGF linear slopes than the adult-implanted participants, irrespective of IPG. IPG sensitivity for AGF linear slope and ECAP threshold did not differ between age groups. Vowel recognition performance was not correlated with any of the ECAP measures assessed in this study. CONCLUSIONS The results of this study support the theory that young CI listeners who were deafened and implanted during childhood may have denser neural populations than older listeners who were deafened and implanted as adults. Potential between-group differences in SGN integrity emphasize a need to investigate optimized CI programming parameters for younger and older listeners.
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Affiliation(s)
- Kelly N. Jahn
- Department of Otolaryngology – Head and Neck Surgery, Harvard Medical School, Boston, MA 02114, USA
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114, USA
| | - Julie G. Arenberg
- Department of Otolaryngology – Head and Neck Surgery, Harvard Medical School, Boston, MA 02114, USA
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114, USA
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Jahn KN, Arenberg JG. Identifying Cochlear Implant Channels With Relatively Poor Electrode-Neuron Interfaces Using the Electrically Evoked Compound Action Potential. Ear Hear 2021; 41:961-973. [PMID: 31972772 PMCID: PMC10443089 DOI: 10.1097/aud.0000000000000844] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES The primary objective of this study was to quantify local (within ear) and global (between ear) variation in the cochlear implant (CI) electrode-neuron interface (ENI) using the electrically evoked compound action potential (ECAP). We tested the hypothesis that, within an ear, ECAP measures can be used to identify channels with presumed good and poor ENIs, which may be influenced by a combination of spiral ganglion neuron (SGN) density, electrode position, and cochlear resistivity. We also hypothesized that ECAP responses would reflect age-related differences in the global quality of the ENI between younger and older listeners who theoretically differ in SGN density. DESIGN Data were obtained from 18 implanted ears (13 individuals) with Advanced Bionics HiRes 90K devices. Six participants (8 ears) were adolescents or young adults (age range: 14-32 years), and 7 participants (10 ears) were older adults (age range: 54-88 years). In each ear, single-channel auditory detection thresholds were measured on channels 2 through 15 in response to a spatially focused electrode configuration (steered quadrupolar; focusing coefficient = 0.9). ECAP amplitudes, amplitude growth function (AGF) slopes, and thresholds were assessed on a subset of channels in each ear in response to three interphase gaps (0, 7, and 30 µs). ECAP peak amplitudes were assessed on all channels between 2 and 15. AGFs and ECAP thresholds were measured on the two nonadjacent channels with the lowest and highest focused behavioral thresholds in each ear. ECAP responses were compared across low- and high-threshold channels and between younger and older CI listeners. RESULTS Channels that were estimated to interface poorly with the auditory nerve (i.e., high-focused-threshold channels) had steeper ECAP AGF slopes, smaller dynamic ranges, and higher ECAP thresholds than channels with low focused thresholds. Younger listeners had steeper ECAP AGF slopes and larger ECAP peak amplitudes than older listeners. Moreover, younger listeners showed greater interphase gap sensitivity for ECAP amplitude than older listeners. CONCLUSIONS ECAP responses may be used to quantify both local (within ear) and global (between ear) variation in the quality of the ENI. Results of this study support future investigation into the use of ECAP responses in site-selection CI programming strategies. The present results also support a growing body of evidence suggesting that adolescents and young adults with CIs may have denser populations of functional SGNs relative to older adults. Potential differences in global SGN integrity between younger and older listeners warrant investigation of optimal CI programming interventions based on their divergent hearing histories.
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Affiliation(s)
- Kelly N. Jahn
- Department of Otolaryngology – Head and Neck Surgery, Harvard Medical School, Boston, MA 02114, USA
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114, USA
| | - Julie G. Arenberg
- Department of Otolaryngology – Head and Neck Surgery, Harvard Medical School, Boston, MA 02114, USA
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114, USA
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Jahn KN, DeVries L, Arenberg JG. Recovery from forward masking in cochlear implant listeners: Effects of age and the electrode-neuron interface. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2021; 149:1633. [PMID: 33765782 PMCID: PMC8267874 DOI: 10.1121/10.0003623] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 02/12/2021] [Accepted: 02/12/2021] [Indexed: 06/12/2023]
Abstract
Older adults exhibit deficits in auditory temporal processing relative to younger listeners. These age-related temporal processing difficulties may be further exacerbated in older adults with cochlear implant (CIs) when CI electrodes poorly interface with their target auditory neurons. The aim of this study was to evaluate the potential interaction between chronological age and the estimated quality of the electrode-neuron interface (ENI) on psychophysical forward masking recovery, a measure that reflects single-channel temporal processing abilities. Fourteen CI listeners (age 15 to 88 years) with Advanced Bionics devices participated. Forward masking recovery was assessed on two channels in each ear (i.e., the channels with the lowest and highest signal detection thresholds). Results indicated that the rate of forward masking recovery declined with advancing age, and that the effect of age was more pronounced on channels estimated to interface poorly with the auditory nerve. These findings indicate that the quality of the ENI can influence the time course of forward masking recovery for older CI listeners. Channel-to-channel variability in the ENI likely interacts with central temporal processing deficits secondary to auditory aging, warranting further study of programming and rehabilitative approaches tailored to older listeners.
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Affiliation(s)
- Kelly N Jahn
- Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington 98105, USA
| | - Lindsay DeVries
- Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742, USA
| | - Julie G Arenberg
- Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington 98105, USA
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Mlynski R, Lüsebrink A, Oberhoffner T, Langner S, Weiss NM. Mapping Cochlear Duct Length to Electrically Evoked Compound Action Potentials in Cochlear Implantation. Otol Neurotol 2021; 42:e254-e260. [PMID: 33273309 DOI: 10.1097/mao.0000000000002957] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
OBJECTIVE Objective measurements may assist in indicating cochlear implants and in predicting outcomes of cochlear implantation surgery. Using electrically evoked compound action potentials (ECAP), information about the function of the auditory nerve can be obtained by analyzing responses to electrical stimulation transmitted and derived by the recording electrode. The aim of this study was to determine whether ECAP characteristics differ depending on the stimulated intracochlear region and the size of the cochlea. STUDY DESIGN Retrospective cohort study. SETTING University Medical center, tertiary academic referral center. PATIENTS Patients undergoing cochlear implant surgery between 2015 and 2018. INTERVENTION Cochlear implantation with FLEXsoft electrode arrays (length 31.5 mm, 12 stimulating channels). MAIN OUTCOME MEASURES The cochlear duct length (CDL) and the cochlear coverage (CC) were measured using a new computed tomography-based software and correlated to the postoperative speech performance. Additionally, ECAP were measured and associated to the CDL. RESULTS A total of 59 ears of 53 cochlear implant users with a mean age of 63.6 (SD 14.9) years were included. The mean estimated CDL was 35.0 (SD 2.2) mm. The mean CC was 90.3% (SD 5.5%). A total of 4,873 ECAP were measured. A statistically significant, moderate, negative correlation between the ECAP slope and the site of stimulation was found (r = -0.29, 95% confidence interval: -0.32 to -0.27, p < 0.0001). No correlation between the CC and the speech performance was found (r = -0.08, 95% confidence interval: -0.33 to 0.18 p = 0.52). CONCLUSION ECAP slopes seem to be a reliable tool to identify the electrode's position inside the cochlea and also showed correlations to the anatomy of the patient. A combination of objective measurements such as anatomical parameters and ECAPs are helpful to assist the postoperative fitting and are promising tools to improve patient care.
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Affiliation(s)
- Robert Mlynski
- Department of Otorhinolaryngology, Head and Neck Surgery "Otto Körner"
| | - Adele Lüsebrink
- Department of Otorhinolaryngology, Head and Neck Surgery "Otto Körner"
| | | | - Soenke Langner
- Department of Radiology, Rostock University Medical Center, Rostock, Germany
| | - Nora M Weiss
- Department of Otorhinolaryngology, Head and Neck Surgery "Otto Körner"
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Jahn KN, Arenberg JG. Polarity Sensitivity in Pediatric and Adult Cochlear Implant Listeners. Trends Hear 2019; 23:2331216519862987. [PMID: 31373266 PMCID: PMC6681263 DOI: 10.1177/2331216519862987] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 06/04/2019] [Accepted: 06/19/2019] [Indexed: 12/02/2022] Open
Abstract
Modeling data suggest that sensitivity to the polarity of an electrical stimulus may reflect the integrity of the peripheral processes of the spiral ganglion neurons. Specifically, better sensitivity to anodic (positive) current than to cathodic (negative) current could indicate peripheral process degeneration or demyelination. The goal of this study was to characterize polarity sensitivity in pediatric and adult cochlear implant listeners (41 ears). Relationships between polarity sensitivity at threshold and (a) polarity sensitivity at suprathreshold levels, (b) age-group, (c) preimplantation duration of deafness, and (d) phoneme perception were determined. Polarity sensitivity at threshold was defined as the difference in single-channel behavioral thresholds measured in response to each of two triphasic pulses, where the central high-amplitude phase was either cathodic or anodic. Lower thresholds in response to anodic than to cathodic pulses may suggest peripheral process degeneration. On the majority of electrodes tested, threshold and suprathreshold sensitivity was lower for anodic than for cathodic stimulation; however, dynamic range was often larger for cathodic than for anodic stimulation. Polarity sensitivity did not differ between child- and adult-implanted listeners. Adults with long preimplantation durations of deafness tended to have better sensitivity to anodic pulses on channels that were estimated to interface poorly with the auditory nerve; this was not observed in the child-implanted group. Across subjects, duration of deafness predicted phoneme perception performance. The results of this study suggest that subject- and electrode-dependent differences in polarity sensitivity may assist in developing customized cochlear implant programming interventions for child- and adult-implanted listeners.
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Affiliation(s)
- Kelly N. Jahn
- Department of Speech and Hearing
Sciences,
University
of Washington, Seattle, WA, USA
| | - Julie G. Arenberg
- Massachusetts Eye and Ear, Department of
Otolaryngology, Harvard Medical School, Boston, MA, USA
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Abstract
Sensorineural hearing impairment is the most common form of hearing loss, and encompasses pathologies of the cochlea and the auditory nerve. Hearing impairment caused by abnormal neural encoding of sound stimuli despite preservation of sensory transduction and amplification by outer hair cells is known as 'auditory neuropathy'. This term was originally coined for a specific type of hearing impairment affecting speech comprehension beyond changes in audibility: patients with this condition report that they "can hear but cannot understand". This type of hearing impairment can be caused by damage to the sensory inner hair cells (IHCs), IHC ribbon synapses or spiral ganglion neurons. Human genetic and physiological studies, as well as research on animal models, have recently shown that disrupted IHC ribbon synapse function--resulting from genetic alterations that affect presynaptic glutamate loading of synaptic vesicles, Ca(2+) influx, or synaptic vesicle exocytosis--leads to hearing impairment termed 'auditory synaptopathy'. Moreover, animal studies have demonstrated that sound overexposure causes excitotoxic loss of IHC ribbon synapses. This mechanism probably contributes to hearing disorders caused by noise exposure or age-related hearing loss. This Review provides an update on recently elucidated sensory, synaptic and neural mechanisms of hearing impairment, their corresponding clinical findings, and discusses current rehabilitation strategies as well as future therapies.
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Affiliation(s)
- Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany
| | - Arnold Starr
- Center for Hearing Research, University of California, Irvine, California 92697, USA
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Iwai H, Inaba M. Fetal thymus graft enables recovery from age-related hearing loss and expansion of CD4-Positive T cells expressing IL-1 receptor type 2 and regulatory T Cells. IMMUNITY & AGEING 2015; 12:26. [PMID: 26673738 PMCID: PMC4678479 DOI: 10.1186/s12979-015-0053-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 12/07/2015] [Indexed: 12/25/2022]
Abstract
Background Accumulating evidence has indicated the relationship between the systemic immune system and the central nervous system including the inner ear. Results We have shown that age-related developments of T-cell dysfunction, hearing loss, and degeneration of cochlear spiral ganglion (SG) neurons observed in 6-month-old mice were recovered in 12 months old mice which previously given fetal thymus transplants twice. We have also demonstrated that CD4+ T cells expressing interleukin 1 receptor type 2 (IL-1R2) and naturally occurring regulatory T cells (nTregs), which expanded in aged 12-month-old mice, were reduced in the thymus-grafted mice of the same age. Conclusion It is conceivable that the rejuvenation of systemic immune function by fetal thymus grafts contributes not only to the activation of cellular immunity but also to the decrease of IL-1R2+ CD4+ T cells or nTregs, which cells accelerate both age-related hearing loss (AHL) and neurodegeneration of the cochlear neurons. Further studies on the interactions among IL-1R2 expression on CD4+ T cells, Tregs, and neuronal cells and also on the relationships between fetal thymus grafting and the rejuvenation of systemic immunity should be designed in order to advance towards therapeutic effects on neurosenescence, including AHL.
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Affiliation(s)
- Hiroshi Iwai
- Department of Otolaryngology, Takii Hospital, Kansai Medical University, Moriguchi, Osaka Japan
| | - Muneo Inaba
- First Department of Medicine, Hirakata Hospital, Kansai Medical University, Hirakata, Osaka Japan
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Local Delivery of Brain-Derived Neurotrophic Factor on the Perforated Round Window Membrane in Guinea Pigs. Otol Neurotol 2015; 36:705-13. [DOI: 10.1097/mao.0000000000000634] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Lu J, Li W, Du X, Ewert DL, West MB, Stewart C, Floyd RA, Kopke RD. Antioxidants reduce cellular and functional changes induced by intense noise in the inner ear and cochlear nucleus. J Assoc Res Otolaryngol 2014; 15:353-72. [PMID: 24497307 PMCID: PMC4010594 DOI: 10.1007/s10162-014-0441-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 01/06/2014] [Indexed: 10/25/2022] Open
Abstract
The present study marks the first evaluation of combined application of the antioxidant N-acetylcysteine (NAC) and the free radical spin trap reagent, disodium 2,4-disulfophenyl-N-tert-butylnitrone (HPN-07), as a therapeutic approach for noise-induced hearing loss (NIHL). Pharmacokinetic studies and C-14 tracer experiments demonstrated that both compounds achieve high blood levels within 30 min after i.p injection, with sustained levels of radiolabeled cysteine (released from NAC) in the cochlea, brainstem, and auditory cortex for up to 48 h. Rats exposed to 115 dB octave-band noise (10-20 kHz) for 1 h were treated with combined NAC/HPN-07 beginning 1 h after noise exposure and for two consecutive days. Auditory brainstem responses (ABR) showed that treatment substantially reduced the degree of threshold shift across all test frequencies (2-16 kHz), beginning at 24 h after noise exposure and continuing for up to 21 days. Reduced distortion product otoacoustic emission (DPOAE) level shifts were also detected at 7 and 21 days following noise exposure in treated animals. Noise-induced hair cell (HC) loss, which was localized to the basal half of the cochlea, was reduced in treated animals by 85 and 64% in the outer and inner HC regions, respectively. Treatment also significantly reduced an increase in c-fos-positive neuronal cells in the cochlear nucleus following noise exposure. However, no detectable spiral ganglion neuron loss was observed after noise exposure. The results reported herein demonstrate that the NAC/HPN-07 combination is a promising pharmacological treatment of NIHL that reduces both temporary and permanent threshold shifts after intense noise exposure and acts to protect cochlear sensory cells, and potentially afferent neurites, from the damaging effects of acoustic trauma. In addition, the drugs were shown to reduce aberrant activation of neurons in the central auditory regions of the brain following noise exposure. It is likely that the protective mechanisms are related to preservation of structural components of the cochlea and blocking the activation of immediate early genes in the auditory centers of the brain.
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Affiliation(s)
- Jianzhong Lu
- />Hough Ear Institute, 3400 N.W. 56th Street, Oklahoma City, OK 73112 USA
| | - Wei Li
- />Hough Ear Institute, 3400 N.W. 56th Street, Oklahoma City, OK 73112 USA
| | - Xiaoping Du
- />Hough Ear Institute, 3400 N.W. 56th Street, Oklahoma City, OK 73112 USA
| | - Donald L. Ewert
- />Hough Ear Institute, 3400 N.W. 56th Street, Oklahoma City, OK 73112 USA
| | - Matthew B. West
- />Hough Ear Institute, 3400 N.W. 56th Street, Oklahoma City, OK 73112 USA
| | - Charles Stewart
- />Oklahoma Medical Research Foundation, Oklahoma City, OK 73104 USA
| | - Robert A. Floyd
- />Oklahoma Medical Research Foundation, Oklahoma City, OK 73104 USA
| | - Richard D Kopke
- />Hough Ear Institute, 3400 N.W. 56th Street, Oklahoma City, OK 73112 USA
- />Oklahoma Medical Research Foundation, Oklahoma City, OK 73104 USA
- />Departments of Physiology and Otolaryngology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104 USA
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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: 131] [Impact Index Per Article: 13.1] [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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Tateno T, Nishikawa J, Tsuchioka N, Shintaku H, Kawano S. A hardware model of the auditory periphery to transduce acoustic signals into neural activity. FRONTIERS IN NEUROENGINEERING 2013; 6:12. [PMID: 24324432 PMCID: PMC3840400 DOI: 10.3389/fneng.2013.00012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 10/28/2013] [Indexed: 11/13/2022]
Abstract
To improve the performance of cochlear implants, we have integrated a microdevice into a model of the auditory periphery with the goal of creating a microprocessor. We constructed an artificial peripheral auditory system using a hybrid model in which polyvinylidene difluoride was used as a piezoelectric sensor to convert mechanical stimuli into electric signals. To produce frequency selectivity, the slit on a stainless steel base plate was designed such that the local resonance frequency of the membrane over the slit reflected the transfer function. In the acoustic sensor, electric signals were generated based on the piezoelectric effect from local stress in the membrane. The electrodes on the resonating plate produced relatively large electric output signals. The signals were fed into a computer model that mimicked some functions of inner hair cells, inner hair cell–auditory nerve synapses, and auditory nerve fibers. In general, the responses of the model to pure-tone burst and complex stimuli accurately represented the discharge rates of high-spontaneous-rate auditory nerve fibers across a range of frequencies greater than 1 kHz and middle to high sound pressure levels. Thus, the model provides a tool to understand information processing in the peripheral auditory system and a basic design for connecting artificial acoustic sensors to the peripheral auditory nervous system. Finally, we discuss the need for stimulus control with an appropriate model of the auditory periphery based on auditory brainstem responses that were electrically evoked by different temporal pulse patterns with the same pulse number.
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Affiliation(s)
- Takashi Tateno
- Special Research Promotion Group, Graduate School of Frontier Biosciences, Osaka University Osaka, Japan ; Biomedical Systems Engineering, Bioengineering and Bioinformatics, Graduate School of Information Science and Technology, Hokkaido University Sapporo, Japan
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Electrically evoked amplitude modulation following response in cochlear implant candidates: comparison with auditory nerve response telemetry, subjective electrical stimulation, and speech perception. Otol Neurotol 2012; 33:968-75. [PMID: 22772009 DOI: 10.1097/mao.0b013e31825e7c5d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To establish the objective, noninvasive recording of the electrically evoked amplitude modulation following response (EAMFR) for the assessment of auditory nerve function in cochlear implant candidates. STUDY DESIGN Prospective clinical study from 2007 to 2010. SETTING Cochlear Implant Programme at the Charité-Universitätsmedizin Berlin (Germany). PATIENTS Thirty-eight patients with severe-to-total bilateral sensorineural hearing impairment. INTERVENTION Diagnostic. MAIN OUTCOME MEASURES The EAMFR thresholds were correlated with the mean thresholds of the intraoperative electrically evoked compound action potential (ECAP) derived by auditory nerve response telemetry and with the subjective electrical stimulation test. The intraindividual left-right similarity of the EAMFR and ECAP thresholds was investigated in 9 bilaterally implanted patients. Additionally, the correlation between auditory performance and EAMFR thresholds was investigated. RESULTS The EAMFR auditory nerve function test produced clear responses in all patients. The EAMFR thresholds correlated significantly with the mean ECAP thresholds (r = 0.58, p < 0.01) and the subjective electrical stimulation test (r = 0.32, p < 0.05). In the bilaterally implanted patients, there was either no side difference, or the ear with the lower preoperative EAMFR threshold also was the one with the lower intraoperative mean ECAP threshold. No correlation was found between EAMFR thresholds and postoperative speech recognition scores. CONCLUSION These novel results support the notion that the EAMFR auditory nerve function test is a useful objective and noninvasive tool to provide information about the responsiveness of the auditory nerve to electrical stimulation in cochlear implant candidates.
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Fetal thymus graft prevents age-related hearing loss and up regulation of the IL-1 receptor type II gene in CD4+ T cells. J Neuroimmunol 2012; 250:1-8. [DOI: 10.1016/j.jneuroim.2012.05.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2012] [Revised: 04/08/2012] [Accepted: 05/04/2012] [Indexed: 12/11/2022]
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Development of brainstem-evoked responses in congenital auditory deprivation. Neural Plast 2012; 2012:182767. [PMID: 22792488 PMCID: PMC3389724 DOI: 10.1155/2012/182767] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 04/17/2012] [Indexed: 11/28/2022] Open
Abstract
To compare the development of the auditory system in hearing and completely acoustically deprived animals, naive congenitally deaf white cats (CDCs) and hearing controls (HCs) were investigated at different developmental stages from birth till adulthood. The CDCs had no hearing experience before the acute experiment. In both groups of animals, responses to cochlear implant stimulation were acutely assessed. Electrically evoked auditory brainstem responses (E-ABRs) were recorded with monopolar stimulation at different current levels. CDCs demonstrated extensive development of E-ABRs, from first signs of responses at postnatal (p.n.) day 3 through appearance of all waves of brainstem response at day 8 p.n. to mature responses around day 90 p.n.. Wave I of E-ABRs could not be distinguished from the artifact in majority of CDCs, whereas in HCs, it was clearly separated from the stimulus artifact. Waves II, III, and IV demonstrated higher thresholds in CDCs, whereas this difference was not found for wave V. Amplitudes of wave III were significantly higher in HCs, whereas wave V amplitudes were significantly higher in CDCs. No differences in latencies were observed between the animal groups. These data demonstrate significant postnatal subcortical development in absence of hearing, and also divergent effects of deafness on early waves II–IV and wave V of the E-ABR.
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Earl BR, Chertoff ME. Mapping auditory nerve firing density using high-level compound action potentials and high-pass noise masking. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2012; 131:337-352. [PMID: 22280596 PMCID: PMC4073701 DOI: 10.1121/1.3664052] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Revised: 10/20/2011] [Accepted: 10/25/2011] [Indexed: 05/28/2023]
Abstract
Future implementation of regenerative treatments for sensorineural hearing loss may be hindered by the lack of diagnostic tools that specify the target(s) within the cochlea and auditory nerve for delivery of therapeutic agents. Recent research has indicated that the amplitude of high-level compound action potentials (CAPs) is a good predictor of overall auditory nerve survival, but does not pinpoint the location of neural damage. A location-specific estimate of nerve pathology may be possible by using a masking paradigm and high-level CAPs to map auditory nerve firing density throughout the cochlea. This initial study in gerbil utilized a high-pass masking paradigm to determine normative ranges for CAP-derived neural firing density functions using broadband chirp stimuli and low-frequency tonebursts, and to determine if cochlear outer hair cell (OHC) pathology alters the distribution of neural firing in the cochlea. Neural firing distributions for moderate-intensity (60 dB pSPL) chirps were affected by OHC pathology whereas those derived with high-level (90 dB pSPL) chirps were not. These results suggest that CAP-derived neural firing distributions for high-level chirps may provide an estimate of auditory nerve survival that is independent of OHC pathology.
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Affiliation(s)
- Brian R Earl
- Department of Hearing and Speech, University of Kansas Medical Center, 3031 Miller, 3901 Rainbow Boulevard, Kansas City, Kansas 66160-7605, USA.
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Pfingst BE, Bowling SA, Colesa DJ, Garadat SN, Raphael Y, Shibata SB, Strahl SB, Su GL, Zhou N. Cochlear infrastructure for electrical hearing. Hear Res 2011; 281:65-73. [PMID: 21605648 PMCID: PMC3208788 DOI: 10.1016/j.heares.2011.05.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2011] [Revised: 04/29/2011] [Accepted: 05/01/2011] [Indexed: 11/30/2022]
Abstract
Although the cochlear implant is already the world's most successful neural prosthesis, opportunities for further improvement abound. Promising areas of current research include work on improving the biological infrastructure in the implanted cochlea to optimize reception of cochlear implant stimulation and on designing the pattern of electrical stimulation to take maximal advantage of conditions in the implanted cochlea. In this review we summarize what is currently known about conditions in the cochlea of deaf, implanted humans and then review recent work from our animal laboratory investigating the effects of preserving or reinnervating tissues on psychophysical and electrophysiological measures of implant function. Additionally we review work from our human laboratory on optimizing the pattern of electrical stimulation to better utilize strengths in the cochlear infrastructure. Histological studies of human temporal bones from implant users and from people who would have been candidates for implants show a range of pathologic conditions including spiral ganglion cell counts ranging from approximately 2% to 92% of normal and partial hair cell survival in some cases. To duplicate these conditions in a guinea pig model, we use a variety of deafening and implantation procedures as well as post-deafening therapies designed to protect neurons and/or regenerate neurites. Across populations of human patients, relationships between nerve survival and functional measures such as speech have been difficult to demonstrate, possibly due to the numerous subject variables that can affect implant function and the elapsed time between functional measures and postmortem histology. However, psychophysical studies across stimulation sites within individual human subjects suggest that biological conditions near the implanted electrodes contribute significantly to implant function, and this is supported by studies in animal models comparing histological findings to psychophysical and electrophysiological data. Results of these studies support the efforts to improve the biological infrastructure in the implanted ear and guide strategies which optimize stimulation patterns to match patient-specific conditions in the cochlea.
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Affiliation(s)
- Bryan E Pfingst
- Department of Otolaryngology, Kresge Hearing Research Institute, University of Michigan, 1150 West Medical Center Drive, Ann Arbor, MI 48109-5616, USA.
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Identifying cochlear implant channels with poor electrode-neuron interfaces: electrically evoked auditory brain stem responses measured with the partial tripolar configuration. Ear Hear 2011; 32:436-44. [PMID: 21178633 DOI: 10.1097/aud.0b013e3181ff33ab] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
OBJECTIVES The goal of this study was to compare cochlear implant behavioral measures and electrically evoked auditory brain stem responses (EABRs) obtained with a spatially focused electrode configuration. It has been shown previously that channels with high thresholds, when measured with the tripolar configuration, exhibit relatively broad psychophysical tuning curves. The elevated threshold and degraded spatial/spectral selectivity of such channels are consistent with a poor electrode-neuron interface, defined as suboptimal electrode placement or reduced nerve survival. However, the psychophysical methods required to obtain these data are time intensive and may not be practical during a clinical mapping session, especially for young children. Here, we have extended the previous investigation to determine whether a physiological approach could provide a similar assessment of channel functionality. We hypothesized that, in accordance with the perceptual measures, higher EABR thresholds would correlate with steeper EABR amplitude growth functions, reflecting a degraded electrode-neuron interface. DESIGN Data were collected from six cochlear implant listeners implanted with the HiRes 90k cochlear implant (Advanced Bionics). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the partial tripolar configuration, for which a fraction of current (σ) from a center active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. EABRs were obtained in each subject for the two channels having the highest and lowest tripolar (σ = 1 or 0.9) behavioral threshold. Evoked potentials were measured with both the monopolar (σ = 0) and a more focused partial tripolar (σ ≥ 0.50) configuration. RESULTS Consistent with previous studies, EABR thresholds were highly and positively correlated with behavioral thresholds obtained with both the monopolar and partial tripolar configurations. The Wave V amplitude growth functions with increasing stimulus level showed the predicted effect of shallower growth for the partial tripolar than for the monopolar configuration, but this was observed only for the low-threshold channels. In contrast, high-threshold channels showed the opposite effect; steeper growth functions were seen for the partial tripolar configuration. CONCLUSIONS These results suggest that behavioral thresholds or EABRs measured with a restricted stimulus can be used to identify potentially impaired cochlear implant channels. Channels having high thresholds and steep growth functions would likely not activate the appropriate spatially restricted region of the cochlea, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.
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The relationship between electrically evoked compound action potential and speech perception: a study in cochlear implant users with short electrode array. Otol Neurotol 2010; 31:1041-8. [PMID: 20634770 DOI: 10.1097/mao.0b013e3181ec1d92] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVES To determine the extent to which electrically evoked compound action potential (ECAP) measurements were related with speech perception performance in implant users with a short electrode array and to investigate the relationship between ECAP measures and performance according to specific devices. DESIGN Prospective study. SETTING Tertiary referral center. PATIENTS Seventeen Hybrid cochlear implant users were tested in this study. Subjects were divided into 2 groups: 8 using the Nucleus Hybrid M and 9 using the Nucleus Hybrid RE. In addition, 21 Nucleus Freedom long electrode implant (CI24RE) users also were tested to compare with the results of the old device (CI24M). MAIN OUTCOME MEASURES ECAP growth functions were recorded using either an interphase gap (IPG) of 8 or 45 mus. We then calculated the slope of the growth function and changes in sensitivity with IPG. For each subject, these measures were compared with performance on tests of word recognition. RESULTS The changes in sensitivity using 2 IPGs showed no correlation with the results of word recognition test in Hybrid cochlear implant users. In contrast, relatively strong correlations have been found between the slope of ECAP growth functions and performance on word recognition test. Additionally, when we separate the results of Hybrid M and RE, the slopes of ECAP growth functions from only Hybrid RE CI recipients were significantly correlated with speech performance. The slopes of ECAP growth function in CI24RE users with long electrode also were significantly correlated with performance. However, comparing between 2 independent correlations in RE devices, correlation was higher in Hybrid RE group. CONCLUSION The results presented in this article support the view that slope of the ECAP growth can show significant correlation to performance with a cochlear implant. Furthermore, these results suggest that the strength of the correlation may be related to the specific device. These results suggest that ECAP measures may be useful in developing a test to predict outcomes with the implant.
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Havenith S, Versnel H, Agterberg MJH, de Groot JCMJ, Sedee RJ, Grolman W, Klis SFL. Spiral ganglion cell survival after round window membrane application of brain-derived neurotrophic factor using gelfoam as carrier. Hear Res 2010; 272:168-77. [PMID: 20969940 DOI: 10.1016/j.heares.2010.10.003] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Revised: 09/17/2010] [Accepted: 10/08/2010] [Indexed: 01/29/2023]
Abstract
Several studies have shown that treatment with various neurotrophins protects spiral ganglion cells (SGCs) from degeneration in hair-cell deprived cochleas. In most of these studies the neurotrophins are delivered by means of intracochlear delivery methods. Recently, other application methods that might be more suited in cochlear implant patients have been developed. We have examined if round window membrane application of gelfoam infiltrated with a neurotrophin resulted in SGC survival in deafened guinea pigs. Two weeks after deafening, gelfoam cubes infiltrated with 6 μg of brain-derived neurotrophic factor (BDNF) were deposited onto the round window membrane of the right cochleas. Electric pulses were delivered through an electrode positioned within the round window niche to electrically evoke auditory brainstem responses (eABRs). Two or four weeks after deposition of the gelfoam all cochleas were histologically examined. We found that local BDNF treatment enhances the survival of SGCs in the basal cochlear turn after two and four weeks. The treatment had no effect on SGC size or shape. In animals treated with BDNF, eABR amplitudes were smaller than in normal-hearing control animals and similar to those in deafened controls. We conclude that BDNF delivered by means of local gelfoam application provides a protective effect, which is limited compared to intracochlear delivery methods.
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Affiliation(s)
- Sarah Havenith
- Department of Otorhinolaryngology and Head & Neck Surgery, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, The Netherlands
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Heffer LF, Sly DJ, Fallon JB, White MW, Shepherd RK, O'Leary SJ. Examining the auditory nerve fiber response to high rate cochlear implant stimulation: chronic sensorineural hearing loss and facilitation. J Neurophysiol 2010; 104:3124-35. [PMID: 20926607 DOI: 10.1152/jn.00500.2010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Neural prostheses, such as cochlear and retinal implants, induce perceptual responses by electrically stimulating sensory nerves. These devices restore sensory system function by using patterned electrical stimuli to evoke neural responses. An understanding of their function requires knowledge of the nerves responses to relevant electrical stimuli as well as the likely effects of pathology on nerve function. We describe how sensorineural hearing loss (SNHL) affects the response properties of single auditory nerve fibers (ANFs) to electrical stimuli relevant to cochlear implants. The response of 188 individual ANFs were recorded in response to trains of stimuli presented at 200, 1,000, 2,000, and 5,000 pulse/s in acutely and chronically deafened guinea pigs. The effects of stimulation rate and SNHL on ANF responses during the 0-2 ms period following stimulus onset were examined to minimize the influence of ANF adaptation. As stimulation rate increased to 5,000 pulse/s, threshold decreased, dynamic range increased and first spike latency decreased. Similar effects of stimulation rate were observed following chronic SNHL, although onset threshold and first spike latency were reduced and onset dynamic range increased compared with acutely deafened animals. Facilitation, defined as an increased nerve excitability caused by subthreshold stimulation, was observed in both acute and chronic SNHL groups, although the magnitude of its effect was diminished in the latter. These results indicate that facilitation, demonstrated here using stimuli similar to those used in cochlear implants, influences the ANF response to pulsatile electrical stimulation and may have important implications for cochlear implant signal processing strategies.
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Affiliation(s)
- Leon F Heffer
- Dept. of Otolaryngology, The University of Melbourne, Royal Victorian Eye and Ear Hospital, Level 2, 32 Gisborne St., East Melbourne, VIC, 3002, Australia.
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Chronic electrical stimulation does not prevent spiral ganglion cell degeneration in deafened guinea pigs. Hear Res 2010; 269:169-79. [DOI: 10.1016/j.heares.2010.06.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 06/16/2010] [Accepted: 06/17/2010] [Indexed: 02/08/2023]
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Abstract
OBJECTIVE Advances in cochlear hair-cell regeneration, neural regeneration, and genetic therapy encourage continued development of diagnostic tests that can accurately specify the appropriate target within the cochlea and auditory nerve for delivery of therapeutic agents. In this study, we test the hypothesis that the morphology of the acoustically evoked compound action potential (CAP) may reflect the condition of the auditory nerve in individuals with sensorineural hearing loss. DESIGN CAPs to tone burst stimuli at octave frequencies from 1 to 16 kHz were recorded at low- to high-stimulus levels from sedated Mongolian gerbils with partial lesions of the auditory nerve (n = 10). Distortion-product otoacoustic emissions were measured to ensure preservation of normal outer hair-cell function. CAPs were analyzed with conventional measures of N1 latency and amplitude and by fitting the CAPs with a mathematical model that includes a parameter (N) representing the number of nerve fibers contributing to the CAP and a parameter (f) representing the oscillation frequency of the CAP waveform. Nerve fiber density and percent normal nerve area were estimated from cross-sections of the auditory nerve bundle. RESULTS Despite substantial lesions in the auditory nerve, CAP thresholds remained within normal or were only moderately elevated and were not correlated with histological measures of nerve fiber density and normal nerve area. At high-stimulus levels, the model parameter N was strongly correlated with nerve fiber density for three of the five test frequencies and with normal nerve area for all five test frequencies. Correlations between N1 amplitude measures at high-stimulus levels and our histological measures were also significant for the majority of test frequencies, but they were generally weaker than the correlations for the model parameter N. The model parameter f, at low- and high-stimulus levels, was also positively correlated with measures of normal nerve area. CONCLUSIONS Consistent with previous findings, physiological measures of threshold were not correlated with partial lesions of the auditory nerve. The model parameter N at high-stimulus levels was strongly correlated with normal nerve area suggesting, that it is a good predictor of auditory nerve survival. The model parameter N also seemed to be a better predictor of the condition of the auditory nerve than the conventional measure of N1 amplitude. Because the model parameter f was correlated with normal nerve area at low- and high-stimulus levels, it may provide information on the functional status of the auditory nerve.
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Abstract
HYPOTHESIS Cell replacement therapy in the inner ear will contribute to the functional recovery of hearing loss. BACKGROUND Cell replacement therapy is a potentially powerful approach to replace degenerated or severely damaged spiral ganglion neurons. This study aimed at stimulating the neurite outgrowth of the implanted neurons and enhancing the potential therapeutic of inner ear cell implants. METHODS Chronic electrical stimulation (CES) and exogenous neurotrophic growth factor (NGF) were applied to 46 guinea pigs transplanted with embryonic dorsal root ganglion (DRG) neurons 4 days postdeafening. The animals were evaluated with the electrically evoked auditory brainstem responses (EABRs) at experimental Days 7, 11, 17, 24, and 31. The animals were euthanized at Day 31, and the inner ears were dissected for immunohistochemistry investigation. RESULTS Implanted DRG cells, identified by enhanced green fluorescent protein fluorescence and a neuronal marker, were found close to Rosenthal canal in the adult inner ear for up to 4 weeks after transplantation. Extensive neurite projections clearly, greater than in nontreated animals, were observed to penetrate the bony modiolus and reach the spiral ganglion region in animals supplied with CES and/or NGF. There was, however, no significant difference in the thresholds of EABRs between DRG-transplanted animals supplied with CES and/or NGF and DRG-transplanted animals without CES or NGF supplement. CONCLUSION The results suggest that CES and/or NGF can stimulate neurite outgrowth from implanted neurons, although based on EABR measurement, these interventions did not induce functional connections to the central auditory pathway. Additional time or novel approaches may enhance functional responsiveness of implanted cells in the adult cochlea.
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Lai WK, Aksit M, Akdas F, Dillier N. Longitudinal behaviour of neural response telemetry (NRT) data and clinical implications. Int J Audiol 2009; 43:252-63. [PMID: 15357408 DOI: 10.1080/14992020400050034] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Neural response telemetry (NRT) data from 63 subjects equipped with the Nucleus CI24M Cochlear Implant System generally exhibited little change over up to 4 years. Larger changes, when they occurred, were seen only within the first 15 months postoperatively, and these changes diminished over time. Intraoperative NRT data were generally stable enough to be used for assisting in the initial speech processor fitting sessions. It was not possible to predict changes in the subjective map threshold and comfortable loudness levels (T and C levels, respectively) based on observed changes in the NRT data. The long-term stability of the neural response amplitude and the neural response threshold, however, implies that NRT may be useful as a routine diagnostic tool to detect changes to the neural periphery over time.
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Affiliation(s)
- Wai Kong Lai
- ENT Department, University Hospital, Zurich, Switzerland.
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Agterberg MJH, Versnel H, van Dijk LM, de Groot JCMJ, Klis SFL. Enhanced survival of spiral ganglion cells after cessation of treatment with brain-derived neurotrophic factor in deafened guinea pigs. J Assoc Res Otolaryngol 2009; 10:355-67. [PMID: 19365690 PMCID: PMC2717388 DOI: 10.1007/s10162-009-0170-2] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Accepted: 03/20/2009] [Indexed: 12/12/2022] Open
Abstract
Exogenous delivery of neurotrophic factors into the cochlea of deafened animals rescues spiral ganglion cells (SGCs) from degeneration. To be clinically relevant for human cochlear implant candidates, the protective effect of neurotrophins should persist after cessation of treatment and the treated SGCs should remain functional. In this study, the survival and functionality of SGCs were investigated after temporary treatment with brain-derived neurotrophic factor (BDNF). Guinea pigs in the experimental group were deafened, and 2 weeks later, the right cochleae were implanted with an electrode array and drug delivery cannula. BDNF was administered to the implanted cochleae during a 4-week period via a mini-osmotic pump. After completion of the treatment, the osmotic pumps were removed. Two weeks later, the animals were killed and the survival of SGCs was analyzed. To monitor the functionality of the auditory nerve, electrically evoked auditory brainstem responses (eABRs) were recorded in awake animals throughout the experiment. BDNF treatment resulted in enhanced survival of SGCs 2 weeks after cessation of the treatment and prevented the decreases in size and circularity that are seen in the untreated contralateral cochleae. The amplitude of the suprathreshold eABR response in BDNF-treated animals was significantly larger than in deafened control animals and comparable to that in normal-hearing control animals. The amplitude in the BDNF-treated group did not decrease significantly after cessation of treatment. The eABR latency in BDNF-treated animals was longer than normal and comparable to that in deafened control animals. These morphological and functional findings demonstrate that neurotrophic intervention had a lasting effect, which is promising for future clinical application of neurotrophic factors in implanted human cochleae.
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Affiliation(s)
- Martijn J H Agterberg
- Department of Otorhinolaryngology, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, GA, Utrecht, The Netherlands
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Jeng FC, Abbas PJ, Hu N, Miller CA, Nourski KV, Robinson BK. Effects of temporal properties on compound action potentials in response to amplitude-modulated electric pulse trains in guinea pigs. Hear Res 2009; 247:47-59. [DOI: 10.1016/j.heares.2008.10.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Revised: 10/21/2008] [Accepted: 10/25/2008] [Indexed: 11/27/2022]
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Chertoff ME, Lichtenhan JT, Tourtillott BM, Esau KS. The influence of noise exposure on the parameters of a convolution model of the compound action potential. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2008; 124:2174-2185. [PMID: 19062857 PMCID: PMC2677342 DOI: 10.1121/1.2967890] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 07/03/2008] [Accepted: 07/08/2008] [Indexed: 05/27/2023]
Abstract
The influence of noise exposure on the parameters of a convolution model of the compound action potential (CAP) was examined. CAPs were recorded in normal-hearing gerbils and in gerbils exposed to a 117 dB SPL 8 kHz band of noise for various durations. The CAPs were fitted with an analytic CAP to obtain the parameters representing the number of nerve fibers (N), the probability density function [P(t)] from a population of nerve fibers, and the single-unit waveform [U(t)]. The results showed that the analytic CAP fitted the physiologic CAPs well with correlations of approximately 0.90. A subsequent analysis using hierarchical linear modeling quantified the change in the parameters as a function of both signal level and hearing threshold. The results showed that noise exposure caused some of the parameter-level functions to simply shift along the signal level axis in proportion to the amount of hearing loss, whereas others shifted along the signal level axis and steepened. Significant changes occurred in the U(t) parameters, but they were not related to hearing threshold. These results suggest that noise exposure alters the physiology underlying the CAP, some of which can be explained by a simple lack of gain, whereas others may not.
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Affiliation(s)
- M E Chertoff
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
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Iwai H, Baba S, Omae M, Lee S, Yamashita T, Ikehara S. Maintenance of systemic immune functions prevents accelerated presbycusis. Brain Res 2008; 1208:8-16. [PMID: 18381209 DOI: 10.1016/j.brainres.2008.02.069] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2007] [Accepted: 02/15/2008] [Indexed: 12/20/2022]
Abstract
There is no effective therapy for progressive hearing loss such as presbycusis, the causes of which remain poorly understood because of the difficulty of separating genetic and environmental contributions. In the present study, we show that the age-related dysfunctions of the systemic immune system in an animal model of accelerated presbycusis (SAMP1, senescence-accelerated mouse P1) can be corrected by allogeneic bone marrow transplantation (BMT). We also demonstrate that this presbycusis can be prevented; BMT protects the recipients from age-related hearing impairment and the degeneration of spiral ganglion cells (SGCs) as well as the dysfunctions of T lymphocytes, which have a close relation to immune senescence. No donor cells are infiltrated to the spiral ganglia, confirming that this experimental system using BMT is connected to the systemic immune system and does not contribute to transdifferentiation or fusion by donor hematopoietic stem cells (HSCs), or to the direct maintenance of ganglion cells by locally infiltrated donor immunocompetent cells. Therefore, another procedure which attempts to prevent the age-related dysfunctions of the recipient immune system is the inoculation of syngeneic splenocytes from young donors. These mice show no development of hearing loss, compared with the recipient mice with inoculation of saline or splenocytes from old donors. Our studies on the relationship between age-related systemic immune dysfunctions and neurodegeneration mechanisms open up new avenues of treatment for presbycusis, for which there is no effective therapy.
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Affiliation(s)
- Hiroshi Iwai
- Department of Otolaryngology, Kansai Medical University, Moriguchi City, Osaka, Japan.
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Jeong SW, Kim LS, Kim BY, Bae WY, Kim JR. Cochlear implantation in children with auditory neuropathy: outcomes and rationale. Acta Otolaryngol 2007:36-43. [PMID: 17882568 DOI: 10.1080/03655230701624848] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
CONCLUSION Children with auditory neuropathy (AN) obtain considerable benefit from cochlear implantation. Their performance outcomes are as good as those of implanted children with sensorineural hearing loss (SNHL). The neural status of children with AN would be comparable to that of children with SNHL and be suitable for cochlear implantation. OBJECTIVE The purpose of this study was to evaluate the outcomes of cochlear implantation in children with AN and to assess the status of auditory nerve in these patients. SUBJECTS AND METHODS Nine children with AN who underwent cochlear implantation were included. Their performance outcomes which were measured by Categories of Auditory Performance (CAP), Monosyllabic Word (MW) test for phonemes, and Common Phrases test were compared with those of matched implanted children with SNHL. To assess the status of auditory nerve in children with AN, the slopes of amplitude growth functions of electrically evoked compound action potentials (ECAPs) in implanted children with AN were compared to those of implanted children with SNHL. RESULTS There were no statistically significant differences between two groups in performance outcomes (CAP, p=0.1200; MW test, p=0.5768; Common Phrases test, p=0.3337). No significant difference was found in the slopes of ECAP amplitude growth functions (p=0.970) between two groups, which shows that spiral ganglion cell populations may be comparable in these two groups.
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Affiliation(s)
- Sung-Wook Jeong
- Department of Otolaryngology-Head and Neck Surgery, College of Medicine, Dong-A University, Busan, Korea
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32
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Pettingill LN, Richardson RT, Wise AK, O'Leary SJ, Shepherd RK. Neurotrophic factors and neural prostheses: potential clinical applications based upon findings in the auditory system. IEEE Trans Biomed Eng 2007; 54:1138-48. [PMID: 17551571 PMCID: PMC1886005 DOI: 10.1109/tbme.2007.895375] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Spiral ganglion neurons (SGNs) are the target cells of the cochlear implant, a neural prosthesis designed to provide important auditory cues to severely or profoundly deaf patients. The ongoing degeneration of SGNs that occurs following a sensorineural hearing loss is, therefore, considered a limiting factor in cochlear implant efficacy. We review neurobiological techniques aimed at preventing SGN degeneration using exogenous delivery of neurotrophic factors. Application of these proteins prevents SGN degeneration and can enhance neurite outgrowth. Furthermore, chronic electrical stimulation of SGNs increases neurotrophic factor-induced survival and is correlated with functional benefits. The application of neurotrophic factors has the potential to enhance the benefits that patients can derive from cochlear implants; moreover, these techniques may be relevant for use with neural prostheses in other neurological conditions.
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MESH Headings
- Animals
- Cell Survival/drug effects
- Cell Survival/physiology
- Cochlea/drug effects
- Cochlea/physiopathology
- Cochlear Implants/trends
- Combined Modality Therapy
- Disease Models, Animal
- Electric Stimulation Therapy/instrumentation
- Electric Stimulation Therapy/methods
- Electrodes, Implanted
- Evoked Potentials, Auditory, Brain Stem/drug effects
- Evoked Potentials, Auditory, Brain Stem/physiology
- Hearing Loss, Sensorineural/pathology
- Hearing Loss, Sensorineural/physiopathology
- Hearing Loss, Sensorineural/therapy
- Membrane Potentials/physiology
- Nerve Degeneration/drug therapy
- Nerve Degeneration/physiopathology
- Nerve Degeneration/prevention & control
- Nerve Growth Factors/administration & dosage
- Neurons, Afferent/drug effects
- Neurons, Afferent/physiology
- Recovery of Function/drug effects
- Recovery of Function/physiology
- Spiral Ganglion/drug effects
- Spiral Ganglion/physiology
- Treatment Outcome
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33
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Eisen MD, Franck KH. Electrically evoked compound action potential amplitude growth functions and HiResolution programming levels in pediatric CII implant subjects. Ear Hear 2005; 25:528-38. [PMID: 15604914 DOI: 10.1097/00003446-200412000-00002] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To characterize the amplitude growth functions of the electrically evoked compound action potential (ECAP) in pediatric subjects implanted with the Clarion HiFocus electrode array with respect to electrode position and the presence or absence of a Silastic positioner. Electrophysiologic growth function data are compared with HiResolution (HiRes) psychophysical programming levels. DESIGN ECAP growth functions were measured for all electrodes along the implant's array in 16 pediatric subjects. Nine of the patients were implanted with a Silastic positioner, whereas seven had no positioner. ECAP thresholds and growth function slopes were calculated. Fifteen of the 16 patients had psychophysical threshold and maximum comfort levels available. Programming levels and ECAP thresholds were compared within and among the subjects. RESULTS ECAP thresholds showed variability among patients, ranging from 178 to 920 nA at 32 musec pulse width. ECAP thresholds did not depend on electrode position along the cochlea but were lower in the presence of the Silastic positioner (p < 0.001). Thresholds determined with the masker-probe versus the alternating polarity paradigms revealed moderate (r = 0.76) correlation. Growth function slopes also showed considerable variation among patients. Unlike thresholds, slopes decreased from apical to basal cochlear locations (p < 0.001) but showed no difference between the absence and presence of the positioner. Programming levels in HiRes were correlated with ECAP threshold levels. When ECAP thresholds were adjusted for each patient by the difference between M level and ECAP threshold at electrode 9, however, overall correlation between the two measurements was excellent (r = 0.98, N = 224). CONCLUSIONS In pediatric subjects with the Clarion HiFocus electrode, ECAP growth function thresholds appear to decrease with the presence of the Silastic positioner but are unaffected by electrode position along the array. Growth function slope, however, depends on electrode position along the array but not on the presence of the positioner. ECAP programming levels can reliably predict stimulus intensities within the patients' dynamic ranges, but considerable variability is seen between ECAP thresholds and HiRes programming levels.
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Affiliation(s)
- Marc D Eisen
- Center for Childhood Communication, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
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Thai-Van H, Truy E, Charasse B, Boutitie F, Chanal JM, Cochard N, Piron JP, Ribas S, Deguine O, Fraysse B, Mondain M, Uziel A, Collet L. Modeling the relationship between psychophysical perception and electrically evoked compound action potential threshold in young cochlear implant recipients: clinical implications for implant fitting. Clin Neurophysiol 2004; 115:2811-24. [PMID: 15546789 DOI: 10.1016/j.clinph.2004.06.024] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/17/2004] [Indexed: 11/20/2022]
Abstract
OBJECTIVE In cochlear implant recipients, the threshold of the electrically evoked compound action potential (ECAP) has been shown to correlate with the perceptual detection threshold and maximum comfortable loudness levels (respectively, T- and C-levels) used for implant programming. Our general objective was to model the relationship between ECAP threshold and T/C-levels by taking into account their relative changes within each subject. In particular, we were interested in investigating further the validity of ECAP threshold as a predictor of psychophysical levels, depending on intra-cochlear electrode location and time of testing (from 1 to 18 months post-implantation). METHODS A total of 370 ECAP thresholds, measured in 49 children, using a Nucleus 24 cochlear implant, were compared with the corresponding T- and C-levels obtained at the same visit, for the same electrode. Response profiles for the whole group of patients were modeled across four test electrodes spaced equally along the electrode array from base towards apex. A linear regression model was constructed and the quality of the ECAP threshold-based predictions was assessed by testing for correlation between measured and predicted psychophysics. Comparison was made with a more simplistic model (described here as the 'parallel profiles method') stipulating, within each subject, a 1 microA increase in psychophysical levels for every 1 microA increase in ECAP threshold. RESULTS Offset between ECAP threshold and psychophysics profiles was found to vary significantly along the electrode array for the T-, but not for the C-level. In contrast with the parallel profiles method, our regression model predicted, within each subject, an average increase of 0.23 microA (95% confidence interval: 0.18-0.28) in T-level for every 1 microA increase in ECAP threshold. This correction improved the quality of T-level prediction when our model was run using measured T-level and ECAP threshold from a reference electrode (r=0.77 vs. r=0.62). The shorter the distance between the electrode for which T-level was predicted and the one used as reference, the stronger the correlation between measured and predicted T-levels. In addition, poorer T-level predictions were obtained at the basal end of the array during the first 3 months post-implantation. In contrast to T-level, individual changes in C-level with ECAP threshold exhibited heterogeneous patterns across subjects so that no common coefficient could account for these changes. However, applying the parallel profiles method led to high-quality C-level prediction. CONCLUSIONS AND SIGNIFICANCE The results suggest that covariation between ECAP thresholds and psychophysics plays a decisive role in the relationship of ECAP threshold with T-, but not with C-level. Therefore, our regression model and the parallel profiles method should both be used for predicting, respectively, the T- and the C-levels. Although the predictability of our regression model seems to be better for middle and apical electrodes, its utilization should be extended to basal electrodes after 6 months' implant use.
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Affiliation(s)
- Hung Thai-Van
- CNRS UMR 5020, IFR 19, Institut Fédératif des Neurosciences de Lyon, Université Claude Bernard, Lyon I, France.
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35
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Chertoff ME. Analytic treatment of the compound action potential: estimating the summed post-stimulus time histogram and unit response. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2004; 116:3022-3030. [PMID: 15603147 DOI: 10.1121/1.1791911] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The convolution of an equation representing a summed post-stimulus time histogram computed across auditory nerve fibers [P(t)] with an equation representing a single-unit wave form [U(t)], resulted in an analytic expression for the compound action potential (CAP). The solution was fit to CAPs recorded to low and high frequency stimuli at various signal levels. The correlation between the CAP and the analytic expression was generally greater than 0.90. At high levels the width of P(t) was broader for low frequency stimuli than for high frequency signals, but delays were comparable. This indicates that at high signal levels there is an overlap in the population of auditory nerve fibers contributing to the CAP for both low and high frequency stimuli but low frequencies include contributions from more apical regions. At low signal levels the width of P(t) decreased for most frequencies and delays increased. The frequency of oscillation of U(t) was largest for high frequency stimuli and decreased for low frequency stimuli. The decay of U(t) was largest at 8 kHz and smallest at 1 kHz. These results indicate that the hair cell or neural mechanisms involved in the generation of action potentials may differ along the cochlear partition.
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Affiliation(s)
- Mark E Chertoff
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66103-0001, USA.
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Polak M, Hodges AV, King JE, Balkany TJ. Further prospective findings with compound action potentials from Nucleus 24 cochlear implants. Hear Res 2004; 188:104-16. [PMID: 14759574 DOI: 10.1016/s0378-5955(03)00309-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2003] [Accepted: 09/24/2003] [Indexed: 11/24/2022]
Abstract
The purpose of this study was to gain greater understanding of compound action potential (CAP) specific characteristics including: slope of the growth function, P1-N1 amplitude, threshold and latencies of P1 and N1 measured in cochlear implant users. Experienced adult subjects underwent behavioral threshold (T) measurement and electrically elicited stapedial reflex (eSR) recording, followed by CAP measurements on six selected electrodes. Based on the electrically elicited stapedial reflex threshold (eSRT), maximum stimulation level for each measured electrode was set. Relationships among the three thresholds of the above measures and maximum CAP P1-N1 amplitude and slope of the growth function were statistically evaluated for each measured electrode. Threshold of the CAP response showed relationships of similar strength with eSRT and T (r=0.69 and 0.61, respectively). For both slope of the growth function and CAP P1-N1 amplitude, a statistically significant relationship with cochlear place was found. Both specific characteristics of CAP measurement for the most apical electrodes were roughly double those for the most basal electrode (alpha=0.05). This may be partially explained by cochlear anatomy and is consistent with prior mammalian and human studies showing increasing density and survival of spiral ganglion cells in the regions corresponding to intracochlear electrode placement from basal to apical electrodes (90-360 degrees ).
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Affiliation(s)
- Marek Polak
- University of Miami Ear Institute, Department of Otolaryngology, 1666 NW 10(th) Ave, ACC East, Miami, FL 33131, USA.
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37
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Lang H, Schulte BA, Schmiedt RA. Effects of chronic furosemide treatment and age on cell division in the adult gerbil inner ear. J Assoc Res Otolaryngol 2003; 4:164-75. [PMID: 12943371 PMCID: PMC3202712 DOI: 10.1007/s10162-002-2056-4] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Atrophy of the stria vascularis and spiral ligament and an associated decrease in the endocochlear potential (EP) are significant factors in age-related hearing loss (presbyacusis). To model this EP decrease, furosemide was delivered into the round-window niche of young adult gerbils by osmotic pump for seven days, chronically reducing the EP by 30-40 mV. Compound action potential (CAP) thresholds were correspondingly reduced by 30-40 dB SPL at high frequencies. Two weeks after withdrawal of furosemide, the treated ears showed an EP recovery of up to 20-30 mV along with a similar recovery of CAP thresholds. The influence of cell division on furosemide-induced and age-related decline of the EP was examined using a mitotic tracer, bromodeoxyuridine (BrdU). Cell proliferation was examined in three groups: young control, furosemide-treated, and aged cochleas. Sections immunostained for BrdU were bleached with H2O2 to eliminate ambiguities with melanin pigment in the inner ear. Cell types positively labeled for BrdU in all three groups included Schwann cells in Rosenthal's canal; glial cells in the osseous spiral lamina; fibrocytes in the limbus, sacculus, and spiral ligament (SL); epithelial cells in Reissner's and round-window membranes; intermediate cells in the stria vascularis; and vascular endothelial cells. Quantitative analysis showed that the mean number of BrdU-positive (BrdU+) intermediate cells in the stria did not differ significantly among the three groups. In contrast, there was a significant increase of BrdU + fibrocytes in the SL of furosemide-treated animals as compared to the young control group. Moreover, there was a significant decrease in labeled fibrocytes in the aged versus the young ears, particularly among the type II and type IV subtypes. The results suggest that the increased fibrocyte turnover in the SL after furosemide treatment may be related to the recovery of EP and CAP thresholds, supporting the hypothesis that fibrocyte proliferation may be essential for maintaining the EP and cochlear function in normal and damaged cochleas. Moreover, the decreased turnover of SL fibrocytes with age may be a contributing factor underlying the lateral wall pathology and consequent EP loss that often accompanies presbyacusis.
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Affiliation(s)
- H. Lang
- Department of Otolaryngology and Head–Neck Surgery, Medical University of South Carolina, Charleston, SC 29425, USA
| | - B. A. Schulte
- Department of Otolaryngology and Head–Neck Surgery, Medical University of South Carolina, Charleston, SC 29425, USA
- Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - R. A. Schmiedt
- Department of Otolaryngology and Head–Neck Surgery, Medical University of South Carolina, Charleston, SC 29425, USA
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Maurer J, Collet L, Pelster H, Truy E, Gallégo S. Auditory late cortical response and speech recognition in Digisonic cochlear implant users. Laryngoscope 2002; 112:2220-4. [PMID: 12461344 DOI: 10.1097/00005537-200212000-00017] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
OBJECTIVE The purpose of the study was to test for differences in late electrically evoked auditory potentials between subjects exhibiting "good" versus "poor" speech recognition performances with their cochlear implants. METHODS Late auditory evoked responses were measured in 30 subjects equipped with the Digisonic (MXM, Antibes, France) cochlear implant, 15 of whom had "good" speech recognition scores (i.e., more than 89% correct phoneme identification without lip reading). The 15 other subjects had poorer speech recognition scores (i.e., less than 85%). RESULTS Differences in N1P2 amplitude, as well as P1, N1, and P2 latencies, and N1-P1 and N1-P2 latency intervals were tested. Wave P2 latency was found to be significantly different between the two groups (P =.016), being shorter in "good" than in "poor" performers. The strength of the statistical relationship between electrophysiological and speech recognition variables (r2 = 17%) was substantially smaller than that observed using electrically evoked auditory brainstem response (EABR) for the same implanted device (r2 = 49% for the EABR wave III-V latency interval). CONCLUSIONS Some characteristics of late electrically evoked auditory potentials differ significantly among cochlear implant users depending on their speech recognition performance. However, the relationship between electrophysiological and speech recognition variables is more pronounced when early (brainstem) rather than late (cortical) evoked responses are considered.
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Affiliation(s)
- Jan Maurer
- Department of Otorhinolaryngology, University of Mainz, Medical School, Germany.
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Firszt JB, Chambers And RD, Kraus N. Neurophysiology of cochlear implant users II: comparison among speech perception, dynamic range, and physiological measures. Ear Hear 2002; 23:516-31. [PMID: 12476089 DOI: 10.1097/00003446-200212000-00003] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE The overall objective of this study was to relate electrically evoked potentials recorded from different levels of the auditory pathway with behavioral measures obtained from adult cochlear implant subjects. The hypothesis was that adult recipients of cochlear implants who have open-set speech perception and those recipients with no open-set speech perception would differ in their neurophysiologic responses recorded at one or more levels of the auditory pathway. DESIGN The subjects were 11 adults implanted with the Clarion cochlear implant. The electrical auditory brainstem response (EABR, Wave V), electrical auditory middle latency response (EAMLR, Na-Pa complex), and the electrical late auditory response (ELAR, N1-P2 complex), were recorded from three intra-cochlear electrodes. The stimuli used to record the evoked potentials varied in rate and amplitude. Behavioral measures (between threshold and upper limit of comfortable loudness) were used to define the subject's dynamic range at the different stimulus rates. Word and sentence recognition tests evaluated subjects' speech perception in quiet and noise. Evoked potential and behavioral measures were examined for statistical significance using analysis of variance for repeated measures and correlational analyses. RESULTS Subjects without open-set speech recognition demonstrated 1) poorly formed or absent evoked potential responses, 2) reduced behavioral dynamic ranges, 3) lack of change in the size of the dynamic range with a change in stimulus rate, and 4) longer periods of auditory deprivation. The variables that differentiated the best performers included 1) presence of responses at all three levels of the auditory pathway, with large normalized amplitudes for the EAMLR, 2) lower evoked potential thresholds for the Na-Pa complex, 3) relatively large dynamic ranges, and 4) changes in the size of the dynamic range with changes in stimulus rate. CONCLUSIONS In this study, the inability to follow changes in the temporal characteristics of the stimulus was associated with poor speech perception performance. Results also illustrate that variability in speech perception scores of cochlear implant recipients relates to neurophysiologic responses at higher cortical levels of the auditory pathway. Presumably, limited neural synchrony for elicitation of electrophysiologic responses underlies limited speech perception. Results confirm that neural encoding with electrical stimulation must provide sufficient physiologic responses of the central nervous system to perceive speech through a cochlear implant.
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Affiliation(s)
- Jill B Firszt
- Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee 53226, USA.
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40
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Sauvaget E, Péréon Y, Nguyen The Tich S, Bordure P. Electrically evoked auditory potentials: comparison between transtympanic promontory and round-window stimulations. Neurophysiol Clin 2002; 32:269-74. [PMID: 12448184 DOI: 10.1016/s0987-7053(02)00308-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
OBJECTIVE Electrically evoked auditory potential (eEAP) techniques have been developed in order to assess electrical excitability of auditory nervous pathways in deaf patients before cochlear implantation. The aim of this study was to compare eEAPs recorded after a transtympanic promontory stimulation with those obtained after a round-window stimulation during a surgical approach. DESIGN eEAPs were recorded after promontory and round-window stimulation in 10 deaf subjects (i.e. 14 ears) who were candidates for cochlear implantation. RESULTS eEAPs were successfully recorded in 13 out of 14 (93%) and 11 out of 14 (79%) ears after promontory stimulation and round-window stimulation, respectively. Similar waveforms, latencies, thresholds and eV amplitudes were observed in both cases. CONCLUSIONS Both tests provide objective and useful information for the patient selection process before cochlear implantation. Transtympanic stimulation should be preferred in clinical practice as it is less invasive than round-window stimulation and does not require surgical exposure.
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Affiliation(s)
- Elisabeth Sauvaget
- Service d'ORL et de chirurgie cervico-faciale, Hôtel-dieu, Nantes, France.
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Dillier N, Lai WK, Almqvist B, Frohne C, Müller-Deile J, Stecker M, von Wallenberg E. Measurement of the electrically evoked compound action potential via a neural response telemetry system. Ann Otol Rhinol Laryngol 2002; 111:407-14. [PMID: 12018325 DOI: 10.1177/000348940211100505] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The main aim of this study was to validate a new technique, neural response telemetry (NRT), for measuring the electrically evoked compound action potential in adult cochlear implant users via their Nucleus C124M implant. Thirty-eight adults were evaluated with a variety of measurement procedures with the NRT software. Electrically evoked compound action potentials were obtained in 31 of the 38 adults (81.6%) and in 132 of the 160 electrodes (82.5%) tested. In addition to validating this technique, we also established a set of default clinical test parameters.
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Affiliation(s)
- Norbert Dillier
- Department of Otorhinolaryngology, University Hospital, Zürich, Switzerland
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Zimmerling MJ, Hochmair ES. EAP recordings in ineraid patients--correlations with psychophysical measures and possible implications for patient fitting. Ear Hear 2002; 23:81-91. [PMID: 11951852 DOI: 10.1097/00003446-200204000-00001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE Objective measurements can be helpful for cochlear implant fitting of difficult populations, as for example very young children. One method, the recording of the electrically evoked compound action potential (EAP), measures the nerve recruitment in the cochlea in response to stimulation through the implant. For coding strategies implemented at a moderate stimulation rate of 250 pps per channel, useful correlations between EAP data and psychophysical data have been already found. With new systems running at higher rates, it is important to check these correlations again. DESIGN This study investigates the correlations between psychophysical data and EAP measures calculated from EAP amplitude growth functions. EAP data were recorded in 12 Ineraid subjects. Additionally, behavioral thresholds (THR) and maximum acceptable loudness levels (MAL) were determined for stimulation rates of 80 pps and 2,020 pps for each electrode. RESULTS Useful correlations between EAP data and psychophysical data were found at the low stimulation rate (80 pps). However, at the higher stimulation rate (2,020 pps) correlations were not significant. They were improved substantially, however, by introducing a factor that corrected for disparities due to temporal integration. Incorporation of this factor, which controls for the influence of the stimulation rate on the threshold, improved the correlations between EAP measures recorded at 80 pps and psychophysical MALs measured at 2,020 pps to better than r = 0.70. CONCLUSIONS EAP data as such can only be used to predict behavioral THRs or MCLs at low stimulation rates. To cope with temporal integration effects at higher stimulation rates, EAP data must be rate corrected. The introduction of a threshold-rate-factor is a promising way to achieve that goal. Further investigations need to be performed.
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Franck KH. A model of a nucleus 24 cochlear implant fitting protocol based on the electrically evoked whole nerve action potential. Ear Hear 2002; 23:67S-71S. [PMID: 11883769 DOI: 10.1097/00003446-200202001-00008] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE The goal of this study was to model a cochlear implant fitting protocol based on the electrically evoked whole nerve action potential (EAP) measured using the Neural Response Telemetry capabilities of the Nucleus C124M cochlear implant. The model and data were based on the significant correlations found between the EAP threshold and growth function slope and psychophysical threshold and, dynamic range, respectively, in 12 subjects (Franck, Reference Note 3; Franck & Norton, 2001). DESIGN Using a retrospective split-half study design, these correlations found between psychophysical mapping levels and EAP data from six of the subjects were used in a model to predict psychophysical mapping levels from EAP data of the other six subjects. RESULTS Predicted psychophysical mapping levels from the model of the EAP-based fitting protocol closely approximated measured cochlear implant fitting psychophysics. CONCLUSIONS The close approximation of the measured data to the model data indicates the feasibility of the clinical use of an EAP-based cochlear implant fitting protocol. The realization of this model would only require two loudness judgments from the patient, whereas traditional fitting requires 44, and would be fit in a live-voice mode, accounting for across-electrode loudness summation.
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Affiliation(s)
- Kevin H Franck
- Center for Childhood Communication, Children's Hospital of Philadelphia, Pennsylvania 19104, USA
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44
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Shepherd RK, Hardie NA. Deafness-induced changes in the auditory pathway: implications for cochlear implants. Audiol Neurootol 2001; 6:305-18. [PMID: 11847461 DOI: 10.1159/000046843] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
A profound sensorineural hearing loss induces significant pathological and atrophic changes within the cochlea and central auditory pathway. We describe these deafness-induced morphological and functional changes following controlled lesions of the cochlea in experimental animals. Such changes are generally consistent with the limited number of reports describing deafness-induced changes observed in human material. The implications of these pathophysiological changes within the auditory pathway on cochlear implant function are discussed. Finally, the plastic response of the deafened auditory system to electrical stimulation of the auditory nerve is reviewed in light of the clinical implications for cochlear implant recipients.
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Affiliation(s)
- R K Shepherd
- Department of Otolaryngology, University of Melbourne, East Melbourne, Vic., Australia.
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Miller CA, Abbas PJ, Brown CJ. An improved method of reducing stimulus artifact in the electrically evoked whole-nerve potential. Ear Hear 2000; 21:280-90. [PMID: 10981604 DOI: 10.1097/00003446-200008000-00003] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE Recording a compound action potential in response to electrical stimulation requires attention to minimize contamination due to electrical stimulus artifact. In patients implanted with the Nucleus 24 device, the electrically evoked whole-nerve potential (EAP) is recorded using a neural response telemetry (NRT) system. This system employs a forward-masking technique that greatly reduces stimulus artifact. However, theoretical considerations and experimental animal data suggest that the technique may distort the acquired EAP waveform under some situations. We proposed and evaluated a modification to the forward-masking technique that addresses this concern, particularly during collection of refractory recovery data. DESIGN We first examined neural responses of the electrically stimulated auditory nerve using cat preparations. Through single-fiber recordings from cats, we demonstrated underlying physiological limitations likely encountered with the "standard" forward masking technique. We then recorded feline EAP waveforms using both the standard technique and our proposed, modified, technique. Finally, we collected EAP data from human cochlear implant patients using both artifact reduction methods. These comparisons allowed us to evaluate the effectiveness of our modification. RESULTS The cat EAP data demonstrated that the standard forward-masking technique currently in use in the Nucleus NRT system can distort the EAP waveform when the nerve is partially refractory. In the cat, this distortion resulted in forward-masking recovery curves with artifactually prolonged recovery times and inaccurate latency trends. Similar effects were observed in the comparison of human recovery curves obtained using both the standard and modified techniques. In some cases, the modified technique produced EAP waveforms with more clearly defined peaks than were obtainable with the standard method. CONCLUSIONS Consideration should be given to implementing our modified forward-masking artifact reduction scheme, because it introduces less distortion of the EAP waveform and accordingly provides for more accurate assessment of the refractory properties of the electrically stimulated nerve.
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Affiliation(s)
- C A Miller
- Department of Speech Pathology and Audiology, University of Iowa, Iowa City, USA
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Saito H, Miller JM, Altschuler RA. Cochleotopic fos immunoreactivity in cochlea and cochlear nuclei evoked by bipolar cochlear electrical stimulation. Hear Res 2000; 145:37-51. [PMID: 10867275 DOI: 10.1016/s0378-5955(00)00070-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Fos-like immunoreactivity evoked by basal, second or apical turn bipolar intracochlear electrical stimulation was evaluated in the spiral ganglion and cochlear nuclei. At stimulation levels of six times the electrically evoked auditory brain stem response thresholds, immunoreactive neurons were observed at appropriate discrete cochleotopic regions relative to stimulation site. The number of neurons increased with stimulus level and closely correlated to wave I amplitude. At 10 times thresholds, some spread in fos-like immunoreactivity to adjacent cochlear turns was found. However, fos-like immunoreactivity at this high level of stimulation still clearly showed a differential distribution in density of expression. These results indicated that the restricted topographic distribution of activity evoked by high levels of electrical stimulation is initiated at first order primary neurons of the system. For the profoundly deaf with cochlear implants, this indicates that place (channel) information can be maintained in the spiral ganglion and central nervous system even at very high levels of electrical stimulation. Together with our previous studies, these results indicate that fos provides a marker which can be used for evaluation of extent and pattern of cellular activation throughout the central auditory pathways, including activation of auditory nerve cells.
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Affiliation(s)
- H Saito
- Department of Otolaryngology, Tokyo Medical College, Tokyo, Japan
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Nikolopoulos TP, Mason SM, Gibbin KP, O'Donoghue GM. The prognostic value of promontory electric auditory brain stem response in pediatric cochlear implantation. Ear Hear 2000; 21:236-41. [PMID: 10890732 DOI: 10.1097/00003446-200006000-00007] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To test the hypothesis that children with clear promontory electrically evoked auditory brain stem responses (prom-EABRs) would outperform, after cochlear implantation, children who had no prom-EABR preoperatively. DESIGN A prospective study was undertaken on 47 implanted children assigning them to two groups (group A: 35 children with a clear wave e-V in the preoperative prom-EABR and group B: 12 children with no prom-EABR). Speech perception and speech intelligibility were assessed annually up to 3 yr after implantation with the IOWA sentence test (level A and level B), Connected Discourse Tracking, Categories of Auditory Performance, and Speech Intelligibility Rating. t-test and Mann-Whitney U test were used to compare the above outcome measures in the two groups. RESULTS There was no statistically significant difference between the two groups on any of the outcome measures at any interval. Moreover, the small differences observed showed no consistent trend toward either group of children. Further analysis revealed that the outcomes have not been affected by possible confounding factors (age at implantation, duration of deafness, preoperative unaided pure-tone thresholds, and number of inserted electrodes). CONCLUSIONS The results suggest that children with no prom-EABR performed at levels comparable with children who had clear promontory responses preoperatively. The prognostic value of prom-EABR is limited and absence of a prom-EABR is not, by itself, a contraindication for cochlear implantation. However, in selected cases (congenital malformations, cochlear nerve dysplasia or suspected aplasia, narrow internal auditory canal, etc.) the presence of a prom-EABR is a positive finding in the assessment of candidates for cochlear implantation as it confirms the existence of intact auditory neurones.
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Affiliation(s)
- T P Nikolopoulos
- Department of Otolaryngology, University Hospital, Queen's Medical Center NHS Trust, Nottingham, United Kingdom
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Mason SM, Dodd M, Gibbin KP, O'Donoghue GM. Assessment of the functioning of peripheral auditory pathways after cochlear re-implantation in young children using intra-operative objective measures. BRITISH JOURNAL OF AUDIOLOGY 2000; 34:179-86. [PMID: 10905451 DOI: 10.3109/03005364000000127] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The intra-operative electrical auditory brainstem response (EABR), electrical stapedius reflex threshold (ESRT) and the early post-operative behavioural threshold level (T-level) were recorded in five children undergoing cochlear re-implantation. The aim of the study was to assess objectively the effect of re-implantation on intra-operative objective measures and to investigate neuronal function. The children were aged between 2.06 years and 4.5 years at first implantation. Following failure of the first device, re-implantation was carried out 1.42-5.52 years later. Characteristics of the EABR and ESRT across the electrode array were typical of the expected pattern of responses on both occasions. In particular, the slopes of the amplitude input/output (I/O) functions for wave eV of the intraoperative EABR were similar for both the first and second implants even though absolute thresholds were generally elevated after re-implantation. This elevation in intra-operative threshold was more pronounced than the change in early post-operative behavioural threshold level for electrical stimulation (T-level). Our findings confirm a high level of neuronal survival after re-implantation. Threshold of the intra-operative EABR at the time of re-implantation greatly underestimates the sensitivity of the subsequent early post-operative T-levels.
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Affiliation(s)
- S M Mason
- Medical Physics Department, Queen's Medical Centre, Nottingham, UK.
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Beitel RE, Snyder RL, Schreiner CE, Raggio MW, Leake PA. Electrical cochlear stimulation in the deaf cat: comparisons between psychophysical and central auditory neuronal thresholds. J Neurophysiol 2000; 83:2145-62. [PMID: 10758124 DOI: 10.1152/jn.2000.83.4.2145] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cochlear prostheses for electrical stimulation of the auditory nerve ("electrical hearing") can provide auditory capacity for profoundly deaf adults and children, including in many cases a restored ability to perceive speech without visual cues. A fundamental challenge in auditory neuroscience is to understand the neural and perceptual mechanisms that make rehabilitation of hearing possible in these deaf humans. We have developed a feline behavioral model that allows us to study behavioral and physiological variables in the same deaf animals. Cats deafened by injection of ototoxic antibiotics were implanted with either a monopolar round window electrode or a multichannel scala tympani electrode array. To evaluate the effects of perceptually significant electrical stimulation of the auditory nerve on the central auditory system, an animal was trained to avoid a mild electrocutaneous shock when biphasic current pulses (0.2 ms/phase) were delivered to its implanted cochlea. Psychophysical detection thresholds and electrical auditory brain stem response (EABR) thresholds were estimated in each cat. At the conclusion of behavioral testing, acute physiological experiments were conducted, and threshold responses were recorded for single neurons and multineuronal clusters in the central nucleus of the inferior colliculus (ICC) and the primary auditory cortex (A1). Behavioral and neurophysiological thresholds were evaluated with reference to cochlear histopathology in the same deaf cats. The results of the present study include: 1) in the cats implanted with a scala tympani electrode array, the lowest ICC and A1 neural thresholds were virtually identical to the behavioral thresholds for intracochlear bipolar stimulation; 2) behavioral thresholds were lower than ICC and A1 neural thresholds in each of the cats implanted with a monopolar round window electrode; 3) EABR thresholds were higher than behavioral thresholds in all of the cats (mean difference = 6.5 dB); and 4) the cumulative number of action potentials for a sample of ICC neurons increased monotonically as a function of the amplitude and the number of stimulating biphasic pulses. This physiological result suggests that the output from the ICC may be integrated spatially across neurons and temporally integrated across pulses when the auditory nerve array is stimulated with a train of biphasic current pulses. Because behavioral thresholds were lower and reaction times were faster at a pulse rate of 30 pps compared with a pulse rate of 2 pps, spatial-temporal integration in the central auditory system was presumably reflected in psychophysical performance.
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Affiliation(s)
- R E Beitel
- Department of Otolaryngology, University of California, San Francisco, California 94143-0732, USA
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Shepherd RK, Linahan N, Xu J, Clark GM, Araki S. Chronic electrical stimulation of the auditory nerve using non-charge-balanced stimuli. Acta Otolaryngol 1999; 119:674-84. [PMID: 10587001 DOI: 10.1080/00016489950180621] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
This study was designed to evaluate the pathophysiological response of the cochlea following long-term intracochlear electrical stimulation using a poorly charge-balanced stimulus regime, leading to direct current (DC) levels >0.1 microA. Four normal-hearing adult cats were bilaterally implanted with scala tympani electrode arrays and unilaterally stimulated for periods up to 2200 h. Stimuli consisted of 50 micros monophasic current pulses presented at 2000 pulses per second (pps) per channel, and resulted in DC levels of 0.4-2.8 microA. Both acoustic and electrical (EABR) evoked potentials were periodically recorded during the stimulation program. Frequency-specific stimuli indicated that an extensive and widespread hearing loss occurred over the 4-24 KHz region in all stimulated cochleae, although the 2 KHz region exhibited thresholds close to normal in some animals, despite long-term implantation and chronic stimulation. Longitudinal EABRs showed a statistically significant increase in threshold for three of the four animals. Histopathological evaluation of the cochleae revealed a highly significant reduction in ganglion cell density in stimulated cochleae compared with their controls. Spiral ganglion cell loss was significantly correlated with the degree of inflammation, duration of electrical stimulation, and the level of DC. In conclusion, the present study highlights the potential for neural damage following stimulation using poorly charge-balanced stimuli.
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Affiliation(s)
- R K Shepherd
- Human Communication Research Centre, Department of Otolaryngology, University of Melbourne, East Melbourne, Victoria, Australia.
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