1
|
Hubka P, Schmidt L, Tillein J, Baumhoff P, Konerding W, Land R, Sato M, Kral A. Dissociated Representation of Binaural Cues in Single-Sided Deafness: Implications for Cochlear Implantation. J Neurosci 2024; 44:e1653232024. [PMID: 38830759 PMCID: PMC11236580 DOI: 10.1523/jneurosci.1653-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2023] [Revised: 04/26/2024] [Accepted: 04/26/2024] [Indexed: 06/05/2024] Open
Abstract
Congenital single-sided deafness (SSD) leads to an aural preference syndrome that is characterized by overrepresentation of the hearing ear in the auditory system. Cochlear implantation (CI) of the deaf ear is an effective treatment for SSD. However, the newly introduced auditory input in congenital SSD often does not reach expectations in late-implanted CI recipients with respect to binaural hearing and speech perception. In a previous study, a reduction of the interaural time difference (ITD) sensitivity has been shown in unilaterally congenitally deaf cats (uCDCs). In the present study, we focused on the interaural level difference (ILD) processing in the primary auditory cortex. The uCDC group was compared with hearing cats (HCs) and bilaterally congenitally deaf cats (CDCs). The ILD representation was reorganized, replacing the preference for the contralateral ear with a preference for the hearing ear, regardless of the cortical hemisphere. In accordance with the previous study, uCDCs were less sensitive to interaural time differences than HCs, resulting in unmodulated ITD responses, thus lacking directional information. Such incongruent ITDs and ILDs cannot be integrated for binaural sound source localization. In normal hearing, the predominant effect of each ear is excitation of the auditory cortex in the contralateral cortical hemisphere and inhibition in the ipsilateral hemisphere. In SSD, however, auditory pathways reorganized such that the hearing ear produced greater excitation in both cortical hemispheres and the deaf ear produced weaker excitation and preserved inhibition in both cortical hemispheres.
Collapse
Affiliation(s)
- Peter Hubka
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
| | - Leonard Schmidt
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
| | - Jochen Tillein
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
- Clinics of Otolaryngology, School of Medicine, J.W. Goethe University, Frankfurt am Main D-60590, Germany
- MedEl GmbH, Starnberg 82319, Germany
| | - Peter Baumhoff
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
| | - Wiebke Konerding
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
| | - Rüdiger Land
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
| | - Mika Sato
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
| | - Andrej Kral
- Department of Experimental Otology, Institute of AudioNeuroTechnology, Clinics of Otolaryngology, Hannover Medical School, Hannover D-30625, Germany
- Australian Hearing Hub, School of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
| |
Collapse
|
2
|
Abstract
The auditory cortex of people with sensorineural hearing loss can be re-afferented using a cochlear implant (CI): a neural prosthesis that bypasses the damaged cells in the cochlea to directly stimulate the auditory nerve. Although CIs are the most successful neural prosthesis to date, some CI users still do not achieve satisfactory outcomes using these devices. To explain variability in outcomes, clinicians and researchers have increasingly focused their attention on neuroscientific investigations that examined how the auditory cortices respond to the electric signals that originate from the CI. This chapter provides an overview of the literature that examined how the auditory cortex changes its functional properties in response to inputs from the CI, in animal models and in humans. We focus first on the basic responses to sounds delivered through electrical hearing and, next, we examine the integrity of two fundamental aspects of the auditory system: tonotopy and processing of binaural cues. When addressing the effects of CIs in humans, we also consider speech-evoked responses. We conclude by discussing to what extent this neuroscientific literature can contribute to clinical practices and help to overcome variability in outcomes.
Collapse
Affiliation(s)
- Francesco Pavani
- Center for Mind/Brain Sciences - CIMeC, University of Trento, Rovereto, Italy.
| | | |
Collapse
|
3
|
Abstract
OBJECTIVE To describe our experience with adults undergoing cochlear implantation (CI) for treatment of single-sided deafness (SSD). STUDY DESIGN Retrospective case review. SETTING Tertiary referral center. PATIENTS Fifty-three adults with SSD. INTERVENTIONS Unilateral CI. MAIN OUTCOME MEASURES Speech perception testing in quiet and noise, tinnitus suppression, and device usage from datalogs. RESULTS The mean age at CI was 53.2 years (SD 11.9). The mean duration of deafness was 4.0 years (SD 7.8). The most common etiology was idiopathic sudden SNHL (50%). Word recognition improved from 8.7% (SD 15) preoperatively to 61.8% (SD 20) at a mean follow-up of 3.3 years (SD 1.8) (p < 0.0001). Adaptive speech recognition testing in the "binaural with CI" condition (speech directed toward the front and noise toward the normal hearing ear) revealed a significant improvement by 2.6-dB SNR compared to the preoperative unaided condition (p = 0.0002) and by 3.6-dB SNR compared to when a device to route sound to the contralateral side was used (p < 0.0001). Tinnitus suppression was reported to be complete in 23 patients (43%) and improved in 20 patients (38%) while the device was on. The addition of the CI did not lead to a decrement in hearing performance in any spatial configuration. Device usage averaged 8.7 (SD 3.7) hours/day. CONCLUSIONS Cochlear implantation in adult SSD patients can suppress tinnitus and achieve speech perception outcomes comparable with CI in conventional candidates. Modest improvements in spatial hearing were also observed and primarily attributable to the head shadow effect. Careful patient selection and counseling regarding potential benefits are important to optimize outcomes.
Collapse
|
4
|
Cortical auditory evoked responses in cochlear implant users with early-onset single-sided deafness: indicators of the development of bilateral auditory pathways. Neuroreport 2019; 29:408-416. [PMID: 29489587 DOI: 10.1097/wnr.0000000000000984] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Cochlear implantation (CI) for early-onset single-sided deafness (SSD) provides a unique insight into the development and cortical reorganization of binaural pathways. This case series aimed to investigate the impact of duration of deafness on CI outcomes as measured by cortical evoked auditory potentials (CAEPs). Four adults with early-onset SSD were studied after CI. The adults had a duration of deafness of 22, 24, 42, and 38 years before implantation. CAEPs and speech perception in noise were used to investigate binaural cortical pathways and function. Our four patients lost their hearing at the ages of 3, 6, 5, and 6 (S1, S2, S3, and S4, respectively). CAEPs were present bilaterally in S2, S3, and S4. S1's, who had the least experience with a CI, cortical responses at 1 month after CI activation showed cortical responses from the CI ipsilateral pathway, but no responses from the CI contralateral pathway. At 3 and 6 months, S1 showed significant cortical responses from the CI contralateral pathway for two speech tokens. An improvement in speech perception in noise testing was observed in all four participants. This case series indicates that long duration of deafness for early-onset SSD is not a contraindication for CI and may not impact the long-term outcomes in this population. The electrical stimulation from the CI integrates with the normal-hearing ear to produce bilateral cortical projections and functional improvement in speech perception in noise. These early data provide surprisingly positive results and call for larger scale research to be carried out.
Collapse
|
5
|
Carlyon RP, Guérit F, Billig AJ, Tam YC, Harris F, Deeks JM. Effect of Chronic Stimulation and Stimulus Level on Temporal Processing by Cochlear Implant Listeners. J Assoc Res Otolaryngol 2019; 20:169-185. [PMID: 30543016 PMCID: PMC6453997 DOI: 10.1007/s10162-018-00706-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 10/29/2018] [Indexed: 01/26/2023] Open
Abstract
A series of experiments investigated potential changes in temporal processing during the months following activation of a cochlear implant (CI) and as a function of stimulus level. Experiment 1 tested patients on the day of implant activation and 2 and 6 months later. All stimuli were presented using direct stimulation of a single apical electrode. The dependent variables were rate discrimination ratios (RDRs) for pulse trains with rates centred on 120 pulses per second (pps), obtained using an adaptive procedure, and a measure of the upper limit of temporal pitch, obtained using a pitch-ranking procedure. All stimuli were presented at their most comfortable level (MCL). RDRs decreased from 1.23 to 1.16 and the upper limit increased from 357 to 485 pps from 0 to 2 months post-activation, with no overall change from 2 to 6 months. Because MCLs and hence the testing level increased across sessions, two further experiments investigated whether the performance changes observed across sessions could be due to level differences. Experiment 2 re-tested a subset of subjects at 9 months post-activation, using current levels similar to those used at 0 months. Although the stimuli sounded softer, some subjects showed lower RDRs and/or higher upper limits at this re-test. Experiment 3 measured RDRs and the upper limit for a separate group of subjects at levels equal to 60 %, 80 % and 100 % of the dynamic range. RDRs decreased with increasing level. The upper limit increased with increasing level for most subjects, with two notable exceptions. Implications of the results for temporal plasticity are discussed, along with possible influences of the effects of level and of across-session learning.
Collapse
Affiliation(s)
- Robert P Carlyon
- Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, UK.
| | - François Guérit
- Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, UK
| | - Alexander J Billig
- Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, UK
| | | | | | - John M Deeks
- Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, UK
| |
Collapse
|
6
|
Chung Y, Buechel BD, Sunwoo W, Wagner JD, Delgutte B. Neural ITD Sensitivity and Temporal Coding with Cochlear Implants in an Animal Model of Early-Onset Deafness. J Assoc Res Otolaryngol 2019; 20:37-56. [PMID: 30623319 DOI: 10.1007/s10162-018-00708-w] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 12/17/2018] [Indexed: 01/04/2023] Open
Abstract
Users of cochlear implant (CI) face challenges in everyday situations such as understanding conversations in noise, even with CIs in both ears. These challenges are related to difficulties with tasks that require fine temporal processing such as discrimination of pulse rates or interaural time differences (ITD), a major cue for sound localization. The degradation in temporal processing and ITD sensitivity are especially acute in those who lost hearing in early childhood. Here, we characterized temporal coding and ITD sensitivity of single neurons in a novel animal model of early-onset deafness. Rabbits were deafened as neonates and deprived of auditory stimulation until they reached adult age when single-unit recordings from the auditory midbrain were made chronically using an unanesthetized preparation. The results are compared to measurements from adult-deafened rabbits with normal auditory development to understand the effect of early-onset deafness on neural temporal coding and ITD sensitivity. Neurons in the inferior colliculus (IC) of early-deafened rabbits were less likely to show sustained, excitatory responses to pulse train stimulation and more likely to show suppressive responses compared to neurons in adult-deaf animals. Fewer neurons showed synchronized responses to pulse trains at any rate in the early-deaf group. In addition, fewer neurons showed significant ITD sensitivity in their overall firing rate in the early-deaf group compared to adult-deaf animals. Neural ITD discrimination thresholds in the early-deaf group were poorer than thresholds in adult-deaf group, especially at high pulse rates. The overall degradation in neural ITD sensitivity is consistent with the difficulties encountered by human CI users with early-onset hearing loss. These results lay the groundwork for investigating whether the degradations in temporal coding and ITD sensitivity observed in early-deaf animals can be reversed by appropriate CI stimulation during development.
Collapse
Affiliation(s)
- Yoojin Chung
- Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA, 02114, USA.
- Department of Otolaryngology, Harvard Medical School, Boston, MA, 02115, USA.
| | - Brian D Buechel
- Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA, 02114, USA
- Program in Speech and Hearing Bioscience and Technology, Harvard Medical School, Boston, MA, 02115, USA
| | - Woongsang Sunwoo
- Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA, 02114, USA
- Department of Otolaryngology, Harvard Medical School, Boston, MA, 02115, USA
- Department of Otolaryngology, Gachon University Gil Medical Center, Incheon, 405-760, South Korea
| | - Joseph D Wagner
- Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA, 02114, USA
| | - Bertrand Delgutte
- Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA, 02114, USA
- Department of Otolaryngology, Harvard Medical School, Boston, MA, 02115, USA
| |
Collapse
|
7
|
Chronic Deafness Degrades Temporal Acuity in the Electrically Stimulated Auditory Pathway. J Assoc Res Otolaryngol 2018; 19:541-557. [PMID: 29968099 PMCID: PMC6226412 DOI: 10.1007/s10162-018-0679-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Accepted: 05/29/2018] [Indexed: 11/28/2022] Open
Abstract
Electrical stimulation of the auditory nerve with a penetrating intraneural (IN) electrode in acutely deafened cats produces much more restricted spread of excitation than is obtained in that preparation with a conventional cochlear implant (CI) as reported by Middlebrooks and Snyder (J Assoc Res Otolaryngol 8:258–279, 2007). That suggests that a future auditory prosthesis employing IN stimulation might offer human patients greater frequency selectivity than is available with a present-day CI. Nevertheless, it is a concern that the electrical field produced by an IN electrode might be too restricted to produce adequate stimulation of the partially depopulated auditory nerve of a deaf patient. We evaluated this by testing responses to IN and CI stimulation in adult-deafened cats. Activation of the auditory pathway was monitored by recording from the central nucleus of the inferior colliculus (ICC). Cats deaf for 153–277 days exhibited a ~ 30 % loss of auditory nerve fibers compared to cats deaf for < 18 h. Contrary to our concern, measures of thresholds and dynamic ranges showed no significant deafness-related impairment of excitation by IN or CN stimulation. Surprisingly, however, temporal acuity decreased dramatically in these adult-deafened cats, as demonstrated by a marked decrease in the maximum rate of electrical cochlear stimulation to which ICC neurons synchronized to IN or CI stimulation. For instance, half of ICC neurons synchronized to IN stimulation up to 203 pulses per second (pps) in acute deafness, whereas that number dropped to 79 pps for chronic deafness. Such a loss of temporal acuity might contribute to the poor sensitivity to temporal fine structure that has been reported in human CI users. Seemingly, the degraded temporal acuity that we observed in cats was even worse than the fine-structure sensitivity of human CI users, suggesting that most patients experience some improvement of temporal acuity resulting from restoration of patterned auditory nerve stimulation by a CI.
Collapse
|
8
|
Berger C, Kühne D, Scheper V, Kral A. Congenital deafness affects deep layers in primary and secondary auditory cortex. J Comp Neurol 2017; 525. [PMID: 28643417 PMCID: PMC5599951 DOI: 10.1002/cne.24267] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Congenital deafness leads to functional deficits in the auditory cortex for which early cochlear implantation can effectively compensate. Most of these deficits have been demonstrated functionally. Furthermore, the majority of previous studies on deafness have involved the primary auditory cortex; knowledge of higher-order areas is limited to effects of cross-modal reorganization. In this study, we compared the cortical cytoarchitecture of four cortical areas in adult hearing and congenitally deaf cats (CDCs): the primary auditory field A1, two secondary auditory fields, namely the dorsal zone and second auditory field (A2); and a reference visual association field (area 7) in the same section stained either using Nissl or SMI-32 antibodies. The general cytoarchitectonic pattern and the area-specific characteristics in the auditory cortex remained unchanged in animals with congenital deafness. Whereas area 7 did not differ between the groups investigated, all auditory fields were slightly thinner in CDCs, this being caused by reduced thickness of layers IV-VI. The study documents that, while the cytoarchitectonic patterns are in general independent of sensory experience, reduced layer thickness is observed in both primary and higher-order auditory fields in layer IV and infragranular layers. The study demonstrates differences in effects of congenital deafness between supragranular and other cortical layers, but similar dystrophic effects in all investigated auditory fields.
Collapse
Affiliation(s)
- Christoph Berger
- Institute of AudioNeuroTechnology & Department of Experimental OtologyENT Clinics, School of Medicine, Hannover Medical UniversityHannoverGermany
| | - Daniela Kühne
- Institute of AudioNeuroTechnology & Department of Experimental OtologyENT Clinics, School of Medicine, Hannover Medical UniversityHannoverGermany
| | - Verena Scheper
- Institute of AudioNeuroTechnology & Department of Experimental OtologyENT Clinics, School of Medicine, Hannover Medical UniversityHannoverGermany
| | - Andrej Kral
- Institute of AudioNeuroTechnology & Department of Experimental OtologyENT Clinics, School of Medicine, Hannover Medical UniversityHannoverGermany
- School of Behavioral and Brain SciencesThe University of TexasDallasUSA
| |
Collapse
|
9
|
Vollmer M, Beitel RE, Schreiner CE, Leake PA. Passive stimulation and behavioral training differentially transform temporal processing in the inferior colliculus and primary auditory cortex. J Neurophysiol 2016; 117:47-64. [PMID: 27733594 DOI: 10.1152/jn.00392.2016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 10/05/2016] [Indexed: 11/22/2022] Open
Abstract
In profoundly deaf cats, behavioral training with intracochlear electric stimulation (ICES) can improve temporal processing in the primary auditory cortex (AI). To investigate whether similar effects are manifest in the auditory midbrain, ICES was initiated in neonatally deafened cats either during development after short durations of deafness (8 wk of age) or in adulthood after long durations of deafness (≥3.5 yr). All of these animals received behaviorally meaningless, "passive" ICES. Some animals also received behavioral training with ICES. Two long-deaf cats received no ICES prior to acute electrophysiological recording. After several months of passive ICES and behavioral training, animals were anesthetized, and neuronal responses to pulse trains of increasing rates were recorded in the central (ICC) and external (ICX) nuclei of the inferior colliculus. Neuronal temporal response patterns (repetition rate coding, minimum latencies, response precision) were compared with results from recordings made in the AI of the same animals (Beitel RE, Vollmer M, Raggio MW, Schreiner CE. J Neurophysiol 106: 944-959, 2011; Vollmer M, Beitel RE. J Neurophysiol 106: 2423-2436, 2011). Passive ICES in long-deaf cats remediated severely degraded temporal processing in the ICC and had no effects in the ICX. In contrast to observations in the AI, behaviorally relevant ICES had no effects on temporal processing in the ICC or ICX, with the single exception of shorter latencies in the ICC in short-deaf cats. The results suggest that independent of deafness duration passive stimulation and behavioral training differentially transform temporal processing in auditory midbrain and cortex, and primary auditory cortex emerges as a pivotal site for behaviorally driven neuronal temporal plasticity in the deaf cat. NEW & NOTEWORTHY Behaviorally relevant vs. passive electric stimulation of the auditory nerve differentially affects neuronal temporal processing in the central nucleus of the inferior colliculus (ICC) and the primary auditory cortex (AI) in profoundly short-deaf and long-deaf cats. Temporal plasticity in the ICC depends on a critical amount of electric stimulation, independent of its behavioral relevance. In contrast, the AI emerges as a pivotal site for behaviorally driven neuronal temporal plasticity in the deaf auditory system.
Collapse
Affiliation(s)
- Maike Vollmer
- Comprehensive Hearing Center, University Hospital Wuerzburg, Wuerzburg, Germany;
| | - Ralph E Beitel
- Coleman Memorial Laboratory, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, California
| | - Christoph E Schreiner
- Center for Integrative Neuroscience, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, California; and
| | - Patricia A Leake
- Epstein Laboratory, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, California
| |
Collapse
|
10
|
Connelly CJ, Ryugo DK, Muniak MA. The effect of progressive hearing loss on the morphology of endbulbs of Held and bushy cells. Hear Res 2016; 343:14-33. [PMID: 27473502 DOI: 10.1016/j.heares.2016.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 07/15/2016] [Accepted: 07/18/2016] [Indexed: 10/21/2022]
Abstract
Studies of congenital and early-onset deafness have demonstrated that an absence of peripheral sound-evoked activity in the auditory nerve causes pathological changes in central auditory structures. The aim of this study was to establish whether progressive acquired hearing loss could lead to similar brain changes that would degrade the precision of signal transmission. We used complementary physiologic hearing tests and microscopic techniques to study the combined effect of both magnitude and duration of hearing loss on one of the first auditory synapses in the brain, the endbulb of Held (EB), along with its bushy cell (BC) target in the anteroventral cochlear nucleus. We compared two hearing mouse strains (CBA/Ca and heterozygous shaker-2+/-) against a model of early-onset progressive hearing loss (DBA/2) and a model of congenital deafness (homozygous shaker-2-/-), examining each strain at 1, 3, and 6 months of age. Furthermore, we employed a frequency model of the mouse cochlear nucleus to constrain our analyses to regions most likely to exhibit graded changes in hearing function with time. No significant differences in the gross morphology of EB or BC structure were observed in 1-month-old animals, indicating uninterrupted development. However, in animals with hearing loss, both EBs and BCs exhibited a graded reduction in size that paralleled the hearing loss, with the most severe pathology seen in deaf 6-month-old shaker-2-/- mice. Ultrastructural pathologies associated with hearing loss were less dramatic: minor changes were observed in terminal size but mitochondrial fraction and postsynaptic densities remained relatively stable. These results indicate that acquired progressive hearing loss can have consequences on auditory brain structure, with prolonged loss leading to greater pathologies. Our findings suggest a role for early intervention with assistive devices in order to mitigate long-term pathology and loss of function.
Collapse
Affiliation(s)
- Catherine J Connelly
- Hearing Research Unit, Garvan Institute of Medical Research, Sydney, NSW 2010, Australia; School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia.
| | - David K Ryugo
- Hearing Research Unit, Garvan Institute of Medical Research, Sydney, NSW 2010, Australia; School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia; Department of Otolaryngology, Head, Neck & Skull Base Surgery, St Vincent's Hospital, Sydney, NSW 2010, Australia
| | - Michael A Muniak
- Hearing Research Unit, Garvan Institute of Medical Research, Sydney, NSW 2010, Australia
| |
Collapse
|
11
|
Balancing current levels in children with bilateral cochlear implants using electrophysiological and behavioral measures. Hear Res 2016; 335:193-206. [PMID: 27021590 DOI: 10.1016/j.heares.2016.03.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 03/21/2016] [Accepted: 03/23/2016] [Indexed: 11/22/2022]
Abstract
Children have benefited from bilateral cochlear implants (CIs) over unilateral CIs despite often missing important periods in bilateral auditory development. This suggests a remarkable perceptual ability by children to "work around" abnormal changes in the auditory pathways. Nonetheless, these children rely primarily on interaural level differences as interaural timing cues are more difficult to access or detect. Mismatched levels provided to the two implants could distort interaural level cues thus compromising the benefits of bilateral CI use. We asked whether "balanced" or "centered" perception of bilateral input can be predicted by physiological or behavioral measures. Twenty-four children who had used unilateral CIs for 9.21 ± 2.66 years prior to bilateral implantation participated. "Balanced bilateral levels" were identified by responses occurring with a probability of 50% on the right side of the head and 50% on the left in a two choice lateralization task. Loudness judgments of current presented unilaterally by each implant were measured on a continuous visual scale. Maximum wave eV amplitudes were evoked unilaterally by each implant and matched amplitudes were identified. Balanced bilateral levels were predicted within 10 Clinical Units (CU) in 9 of 13 (69%) children using matched wave eV amplitudes. Bilaterally balanced levels were reasonably predicted by similar loudness judgments (<10% difference between CIs) in only 6 of 13 (46%) children. Results indicate that matching amplitudes of physiological responses can produce a balanced perception of bilateral input despite unilateral strengthening of the auditory pathways and can potentially be used clinically to provide a first approximation of balance/centered levels.
Collapse
|
12
|
Somatic memory and gain increase as preconditions for tinnitus: Insights from congenital deafness. Hear Res 2016; 333:37-48. [DOI: 10.1016/j.heares.2015.12.018] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Revised: 11/27/2015] [Accepted: 12/18/2015] [Indexed: 11/19/2022]
|
13
|
Tillein J, Hubka P, Kral A. Monaural Congenital Deafness Affects Aural Dominance and Degrades Binaural Processing. Cereb Cortex 2016; 26:1762-77. [PMID: 26803166 PMCID: PMC4785956 DOI: 10.1093/cercor/bhv351] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Cortical development extensively depends on sensory experience. Effects of congenital monaural and binaural deafness on cortical aural dominance and representation of binaural cues were investigated in the present study. We used an animal model that precisely mimics the clinical scenario of unilateral cochlear implantation in an individual with single-sided congenital deafness. Multiunit responses in cortical field A1 to cochlear implant stimulation were studied in normal-hearing cats, bilaterally congenitally deaf cats (CDCs), and unilaterally deaf cats (uCDCs). Binaural deafness reduced cortical responsiveness and decreased response thresholds and dynamic range. In contrast to CDCs, in uCDCs, cortical responsiveness was not reduced, but hemispheric-specific reorganization of aural dominance and binaural interactions were observed. Deafness led to a substantial drop in binaural facilitation in CDCs and uCDCs, demonstrating the inevitable role of experience for a binaural benefit. Sensitivity to interaural time differences was more reduced in uCDCs than in CDCs, particularly at the hemisphere ipsilateral to the hearing ear. Compared with binaural deafness, unilateral hearing prevented nonspecific reduction in cortical responsiveness, but extensively reorganized aural dominance and binaural responses. The deaf ear remained coupled with the cortex in uCDCs, demonstrating a significant difference to deprivation amblyopia in the visual system.
Collapse
Affiliation(s)
- Jochen Tillein
- Cluster of Excellence Hearing4all, Institute of AudioNeuroTechnology and Department of Experimental Otology of the ENT Clinics, Hannover Medical School, Hannover, Germany Department of Otorhinolaryngology, J.W. Goethe University, Frankfurt am Main, Germany MED-EL GmbH, Innsbruck, Austria
| | - Peter Hubka
- Cluster of Excellence Hearing4all, Institute of AudioNeuroTechnology and Department of Experimental Otology of the ENT Clinics, Hannover Medical School, Hannover, Germany
| | - Andrej Kral
- Cluster of Excellence Hearing4all, Institute of AudioNeuroTechnology and Department of Experimental Otology of the ENT Clinics, Hannover Medical School, Hannover, Germany School of Behavioral and Brain Sciences, The University of Texas at Dallas, Richardson, TX, USA
| |
Collapse
|
14
|
Boisvert I, McMahon CM, Dowell RC, Lyxell B. Long-term asymmetric hearing affects cochlear implantation outcomes differently in adults with pre- and postlingual hearing loss. PLoS One 2015; 10:e0129167. [PMID: 26043227 PMCID: PMC4456415 DOI: 10.1371/journal.pone.0129167] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Accepted: 05/05/2015] [Indexed: 02/01/2023] Open
Abstract
In many countries, a single cochlear implant is offered as a treatment for a bilateral hearing loss. In cases where there is asymmetry in the amount of sound deprivation between the ears, there is a dilemma in choosing which ear should be implanted. In many clinics, the choice of ear has been guided by an assumption that the reorganisation of the auditory pathways caused by longer duration of deafness in one ear is associated with poorer implantation outcomes for that ear. This assumption, however, is mainly derived from studies of early childhood deafness. This study compared outcomes following implantation of the better or poorer ear in cases of long-term hearing asymmetries. Audiological records of 146 adults with bilateral hearing loss using a single hearing aid were reviewed. The unaided ear had 15 to 72 years of unaided severe to profound hearing loss before unilateral cochlear implantation. 98 received the implant in their long-term sound-deprived ear. A multiple regression analysis was conducted to assess the relative contribution of potential predictors to speech recognition performance after implantation. Duration of bilateral significant hearing loss and the presence of a prelingual hearing loss explained the majority of variance in speech recognition performance following cochlear implantation. For participants with postlingual hearing loss, similar outcomes were obtained by implanting either ear. With prelingual hearing loss, poorer outcomes were obtained when implanting the long-term sound-deprived ear, but the duration of the sound deprivation in the implanted ear did not reliably predict outcomes. Contrary to an apparent clinical consensus, duration of sound deprivation in one ear has limited value in predicting speech recognition outcomes of cochlear implantation in that ear. Outcomes of cochlear implantation are more closely related to the period of time for which the brain is deprived of auditory stimulation from both ears.
Collapse
Affiliation(s)
- Isabelle Boisvert
- Department Linguistics, Macquarie University, Sydney, New South Wales, Australia
- HEARing Cooperative Research Centre, Melbourne, Victoria, Australia
- SCIC Cochlear Implant Program - An RIDBC service, Sydney, New South Wales, Australia
- Linnaeus Centre HEAD, The Swedish Institute for Disability Research, Linköping, Sweden
- * E-mail:
| | - Catherine M. McMahon
- Department Linguistics, Macquarie University, Sydney, New South Wales, Australia
- HEARing Cooperative Research Centre, Melbourne, Victoria, Australia
| | - Richard C. Dowell
- HEARing Cooperative Research Centre, Melbourne, Victoria, Australia
- Department of Audiology and Speech Pathology, The University of Melbourne, Melbourne, Victoria, Australia
- Audiology, Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia
| | - Björn Lyxell
- Department of Behavioural Sciences and Learning, Linköping University, Linköping, Sweden
- Linnaeus Centre HEAD, The Swedish Institute for Disability Research, Linköping, Sweden
| |
Collapse
|
15
|
Kral A, Hubka P, Tillein J. Strengthening of hearing ear representation reduces binaural sensitivity in early single-sided deafness. Audiol Neurootol 2015; 20 Suppl 1:7-12. [PMID: 25998842 DOI: 10.1159/000380742] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Single-sided deafness initiates extensive adaptations in the central auditory system, with the consequence that a stronger and a weaker ear representation develops in the auditory brain. Animal studies demonstrated that the effects are substantially stronger if the condition starts early in development. Sequential binaural cochlear implantations with longer interimplant delays demonstrate that the speech comprehension at the weaker ear is substantially compromised. A pronounced loss of the ability to extract and represent binaural localisation cues accompanies this condition, as shown in animal models.
Collapse
Affiliation(s)
- Andrej Kral
- Institute of AudioNeuroTechnology and Department of Experimental Otology, ENT Clinics, School of Medicine, Hannover Medical University, Hannover, Germany
| | | | | |
Collapse
|
16
|
Objective measures of electrode discrimination with electrically evoked auditory change complex and speech-perception abilities in children with auditory neuropathy spectrum disorder. Ear Hear 2015; 35:e63-74. [PMID: 24231629 DOI: 10.1097/01.aud.0000436605.92129.1b] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVES This study aimed to (1) determine the sensitivity of the electrically evoked auditory change complex (eACC) to changes in stimulating electrode position; and (2) investigate the association between results of eACC measures and behavioral electrode discrimination and their association with speech-perception performance in pediatric cochlear implant (CI) users who have auditory neuropathy spectrum disorder (ANSD). DESIGN Fifteen children with ANSD ranging in age between 5.4 and 18.6 years participated in this study. All subjects used Cochlear Nucleus devices. For each subject, open-set speech-perception ability was assessed using the Phonetically Balanced Kindergarten word lists presented at 60 dB SPL, using monitored live voice in a sound booth. Behavioral and objective measures of electrode discrimination were assessed in a nonclinical test environment. The stimuli used to elicit these measures were 800 msec biphasic pulse trains delivered by a direct interface to the CI. Data were collected from two basic stimulation conditions. In the standard condition, the entire pulse train was delivered to a mid-array electrode (electrode 11 or 12) at the maximum comfortable level (C level). In the change condition, the stimulus was split into two 400 msec pulse train segments presented sequentially on two different electrodes. The stimulation level of the second 400 msec pulse train was loudness balanced to the C level of the mid-array electrode used in the standard condition. The separation between the pair of stimulating electrodes was systematically varied. For behavioral electrode-discrimination measures, each subject was required to determine whether he or she heard one or two sounds for stimuli presented in different stimulation conditions. For the eACC measures, two replicates of 100 artifact-free sweeps were recorded for each stimulation condition. RESULTS The eACC in response to changes in stimulating electrode position was recorded from all subjects with ANSD using direct electrical stimulation. Electrode-discrimination thresholds determined with the eACC and behavioral measures were consistent. Children with ANSD using CIs who showed poorer speech performance also required larger separations between the stimulating electrode pair to reliably elicit the eACC than subjects with better speech-perception performance. There was a robust correlation between electrode-discrimination capacities and speech-perception performances in subjects tested in this study. The effect of electrode separation on eACC amplitudes was not monotonic. CONCLUSIONS These results demonstrate the feasibility of using eACC to evaluate electrode-discrimination capacities in children with ANSD. These results suggest that the eACC elicited by changes in stimulating electrode position holds great promise as an objective tool for evaluating spectral-pattern detection in such subjects, which may be predictive of their potential speech-perception performance.
Collapse
|
17
|
Auditory neuroplasticity, hearing loss and cochlear implants. Cell Tissue Res 2014; 361:251-69. [DOI: 10.1007/s00441-014-2004-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/04/2014] [Indexed: 10/24/2022]
|
18
|
Morphological and physiological development of auditory synapses. Hear Res 2014; 311:3-16. [PMID: 24508369 DOI: 10.1016/j.heares.2014.01.007] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2013] [Revised: 01/13/2014] [Accepted: 01/20/2014] [Indexed: 02/07/2023]
Abstract
Acoustic communication requires gathering, transforming, and interpreting diverse sound cues. To achieve this, all the spatial and temporal features of complex sound stimuli must be captured in the firing patterns of the primary sensory neurons and then accurately transmitted along auditory pathways for additional processing. The mammalian auditory system relies on several synapses with unique properties in order to meet this task: the auditory ribbon synapses, the endbulb of Held, and the calyx of Held. Each of these synapses develops morphological and electrophysiological characteristics that enable the remarkably precise signal transmission necessary for conveying the miniscule differences in timing that underly sound localization. In this article, we review the current knowledge of how these synapses develop and mature to acquire the specialized features necessary for the sense of hearing.
Collapse
|
19
|
Kral A, Heid S, Hubka P, Tillein J. Unilateral hearing during development: hemispheric specificity in plastic reorganizations. Front Syst Neurosci 2013; 7:93. [PMID: 24348345 PMCID: PMC3841817 DOI: 10.3389/fnsys.2013.00093] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 11/05/2013] [Indexed: 02/04/2023] Open
Abstract
The present study investigates the hemispheric contributions of neuronal reorganization following early single-sided hearing (unilateral deafness). The experiments were performed on ten cats from our colony of deaf white cats. Two were identified in early hearing screening as unilaterally congenitally deaf. The remaining eight were bilaterally congenitally deaf, unilaterally implanted at different ages with a cochlear implant. Implanted animals were chronically stimulated using a single-channel portable signal processor for two to five months. Microelectrode recordings were performed at the primary auditory cortex under stimulation at the hearing and deaf ear with bilateral cochlear implants. Local field potentials (LFPs) were compared at the cortex ipsilateral and contralateral to the hearing ear. The focus of the study was on the morphology and the onset latency of the LFPs. With respect to morphology of LFPs, pronounced hemisphere-specific effects were observed. Morphology of amplitude-normalized LFPs for stimulation of the deaf and the hearing ear was similar for responses recorded at the same hemisphere. However, when comparisons were performed between the hemispheres, the morphology was more dissimilar even though the same ear was stimulated. This demonstrates hemispheric specificity of some cortical adaptations irrespective of the ear stimulated. The results suggest a specific adaptation process at the hemisphere ipsilateral to the hearing ear, involving specific (down-regulated inhibitory) mechanisms not found in the contralateral hemisphere. Finally, onset latencies revealed that the sensitive period for the cortex ipsilateral to the hearing ear is shorter than that for the contralateral cortex. Unilateral hearing experience leads to a functionally-asymmetric brain with different neuronal reorganizations and different sensitive periods involved.
Collapse
Affiliation(s)
- Andrej Kral
- Cluster of Excellence, Department of Experimental Otology, Institute of Audioneurotechnology, ENT Clinics, Hannover Medical School Hannover, Germany
| | - Silvia Heid
- Cluster of Excellence, Department of Experimental Otology, Institute of Audioneurotechnology, ENT Clinics, Hannover Medical School Hannover, Germany ; Department of Physiology and Otolaryngology, J. W. Goethe University Frankfurt am Main, Germany
| | - Peter Hubka
- Cluster of Excellence, Department of Experimental Otology, Institute of Audioneurotechnology, ENT Clinics, Hannover Medical School Hannover, Germany
| | - Jochen Tillein
- Cluster of Excellence, Department of Experimental Otology, Institute of Audioneurotechnology, ENT Clinics, Hannover Medical School Hannover, Germany ; Department of Physiology and Otolaryngology, J. W. Goethe University Frankfurt am Main, Germany
| |
Collapse
|
20
|
Gordon KA, Jiwani S, Papsin BC. Benefits and detriments of unilateral cochlear implant use on bilateral auditory development in children who are deaf. Front Psychol 2013; 4:719. [PMID: 24137143 PMCID: PMC3797443 DOI: 10.3389/fpsyg.2013.00719] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2013] [Accepted: 09/18/2013] [Indexed: 12/04/2022] Open
Abstract
We have explored both the benefits and detriments of providing electrical input through a cochlear implant in one ear to the auditory system of young children. A cochlear implant delivers electrical pulses to stimulate the auditory nerve, providing children who are deaf with access to sound. The goals of implantation are to restrict reorganization of the deprived immature auditory brain and promote development of hearing and spoken language. It is clear that limiting the duration of deprivation is a key factor. Additional considerations are the onset, etiology, and use of residual hearing as each of these can have unique effects on auditory development in the pre-implant period. New findings show that many children receiving unilateral cochlear implants are developing mature-like brainstem and thalamo-cortical responses to sound with long term use despite these sources of variability; however, there remain considerable abnormalities in cortical function. The most apparent, determined by implanting the other ear and measuring responses to acute stimulation, is a loss of normal cortical response from the deprived ear. Recent data reveal that this can be avoided in children by early implantation of both ears simultaneously or with limited delay. We conclude that auditory development requires input early in development and from both ears.
Collapse
Affiliation(s)
- Karen A. Gordon
- Archie’s Cochlear Implant Laboratory, The Hospital for Sick ChildrenToronto, ON, Canada
- Institute of Medical Sciences, Faculty of Medicine, University of TorontoToronto, ON, Canada
- Department of Otolaryngology – Head and Neck surgery, Faculty of Medicine, University of TorontoToronto, ON, Canada
| | - Salima Jiwani
- Archie’s Cochlear Implant Laboratory, The Hospital for Sick ChildrenToronto, ON, Canada
- Institute of Medical Sciences, Faculty of Medicine, University of TorontoToronto, ON, Canada
| | - Blake C. Papsin
- Archie’s Cochlear Implant Laboratory, The Hospital for Sick ChildrenToronto, ON, Canada
- Department of Otolaryngology – Head and Neck surgery, Faculty of Medicine, University of TorontoToronto, ON, Canada
| |
Collapse
|
21
|
|
22
|
Lauer AM, Connelly CJ, Graham H, Ryugo DK. Morphological characterization of bushy cells and their inputs in the laboratory mouse (Mus musculus) anteroventral cochlear nucleus. PLoS One 2013; 8:e73308. [PMID: 23991186 PMCID: PMC3753269 DOI: 10.1371/journal.pone.0073308] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Accepted: 07/19/2013] [Indexed: 11/18/2022] Open
Abstract
Spherical and globular bushy cells of the AVCN receive huge auditory nerve endings specialized for high fidelity neural transmission in response to acoustic events. Recent studies in mice and other rodent species suggest that the distinction between bushy cell subtypes is not always straightforward. We conducted a systematic investigation of mouse bushy cells along the rostral-caudal axis in an effort to understand the morphological variation that gives rise to reported response properties in mice. We combined quantitative light and electron microscopy to investigate variations in cell morphology, immunostaining, and the distribution of primary and non-primary synaptic inputs along the rostral-caudal axis. Overall, large regional differences in bushy cell characteristics were not found; however, rostral bushy cells received a different complement of axosomatic input compared to caudal bushy cells. The percentage of primary auditory nerve terminals was larger in caudal AVCN, whereas non-primary excitatory and inhibitory inputs were more common in rostral AVCN. Other ultrastructural characteristics of primary auditory nerve inputs were similar across the rostral and caudal AVCN. Cross sectional area, postsynaptic density length and curvature, and mitochondrial volume fraction were similar for axosomatic auditory nerve terminals, although rostral auditory nerve terminals contained a greater concentration of synaptic vesicles near the postsynaptic densities. These data demonstrate regional differences in synaptic organization of inputs to mouse bushy cells rather than the morphological characteristic of the cells themselves.
Collapse
Affiliation(s)
- Amanda M Lauer
- Department of Otolaryngology-HNS, Johns Hopkins University, Baltimore, MD, USA.
| | | | | | | |
Collapse
|
23
|
Hancock KE, Chung Y, Delgutte B. Congenital and prolonged adult-onset deafness cause distinct degradations in neural ITD coding with bilateral cochlear implants. J Assoc Res Otolaryngol 2013; 14:393-411. [PMID: 23462803 PMCID: PMC3642270 DOI: 10.1007/s10162-013-0380-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 02/15/2013] [Indexed: 10/27/2022] Open
Abstract
Bilateral cochlear implant (CI) users perform poorly on tasks involving interaural time differences (ITD), which are critical for sound localization and speech reception in noise by normal-hearing listeners. ITD perception with bilateral CI is influenced by age at onset of deafness and duration of deafness. We previously showed that ITD coding in the auditory midbrain is degraded in congenitally deaf white cats (DWC) compared to acutely deafened cats (ADC) with normal auditory development (Hancock et al., J. Neurosci, 30:14068). To determine the relative importance of early onset of deafness and prolonged duration of deafness for abnormal ITD coding in DWC, we recorded from single units in the inferior colliculus of cats deafened as adults 6 months prior to experimentation (long-term deafened cats, LTDC) and compared neural ITD coding between the three deafness models. The incidence of ITD-sensitive neurons was similar in both groups with normal auditory development (LTDC and ADC), but significantly diminished in DWC. In contrast, both groups that experienced prolonged deafness (LTDC and DWC) had broad distributions of best ITDs around the midline, unlike the more focused distributions biased toward contralateral-leading ITDs present in both ADC and normal-hearing animals. The lack of contralateral bias in LTDC and DWC results in reduced sensitivity to changes in ITD within the natural range. The finding that early onset of deafness more severely degrades neural ITD coding than prolonged duration of deafness argues for the importance of fitting deaf children with sound processors that provide reliable ITD cues at an early age.
Collapse
Affiliation(s)
- Kenneth E. Hancock
- />Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA 02114 USA
- />Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02115 USA
| | - Yoojin Chung
- />Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA 02114 USA
- />Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02115 USA
| | - Bertrand Delgutte
- />Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA 02114 USA
- />Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02115 USA
- />Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| |
Collapse
|
24
|
Kral A, Hubka P, Heid S, Tillein J. Single-sided deafness leads to unilateral aural preference within an early sensitive period. ACTA ACUST UNITED AC 2012; 136:180-93. [PMID: 23233722 DOI: 10.1093/brain/aws305] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Unilateral deafness has a high incidence in children. In addition to children who are born without hearing in one ear, children with bilateral deafness are frequently equipped only with one cochlear implant, leaving the other ear deaf. The present study investigates the effects of such single-sided deafness during development in the congenitally deaf cat. The investigated animals were either born with unilateral deafness or received a cochlear implant in one ear and were subjected to chronic monaural stimulation. In chronically stimulated animals, implantation ages were at the following three critical developmental points: 'early' during the peak of functional cortical synaptogenesis in deaf animals; 'intermediate' at the age when synaptic activity in the deaf cats dropped to the level of hearing control cats and finally, 'late' at the age when the evoked synaptic activity fell below the level of hearing control cats. After periods of unilateral hearing, local field potentials were recorded from the cortical surface using a microelectrode at ∼100 recording positions. Stimulation was with cochlear implants at both ears. The measures evaluated were dependent only on the symmetry of aural input: paired differences of onset latencies and paired relations of peak amplitudes of local field potentials. A massive reorganization of aural preference in favour of the hearing ear was found in these measures if the onset of unilateral hearing was early (before or around the peak of functional synaptogenesis). The effect was reduced if onset of unilateral hearing was in the intermediate period, and it disappeared if the onset was late. In early onset of unilateral deafness, the used ear became functionally dominant with respect to local field potential onset latency and amplitude. This explains the inferior outcome of implantations at the second-implanted ear compared with first-implanted ear in children. However, despite a central disadvantage for the deaf ear, it still remained capable of activating the auditory cortex. Appropriate training may thus help to improve the performance at the second-implanted ear. In conclusion, periods of monaural stimulation should be kept as short as possible, and training focused on the deaf ear should be introduced after delayed second implantation in children.
Collapse
Affiliation(s)
- Andrej Kral
- Institute of Audioneurotechnology, Feodor-Lynen-Strasse 35, D-30625 Hannover, Germany.
| | | | | | | |
Collapse
|
25
|
Abstract
Cats have among the best hearing of all mammals in that they are extremely sensitive to a broad range of frequencies. The ear is a highly complex structure that is delicately balanced in terms of its biochemistry, types of receptors, ion channels, mechanical properties, and cellular organization. Sensorineural deafness is caused by "flawed" genes that are inherited from one or both parents. Hearing loss can also be acquired as a result of noise trauma from industrialized environment, viral infection, or blunt trauma. To date, it is not practical to intervene and attempt to correct these forms of deafness in cats.
Collapse
Affiliation(s)
- David K Ryugo
- Hearing Research Program, Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia.
| | | |
Collapse
|
26
|
Tirko NN, Ryugo DK. Synaptic plasticity in the medial superior olive of hearing, deaf, and cochlear-implanted cats. J Comp Neurol 2012; 520:2202-17. [PMID: 22237661 DOI: 10.1002/cne.23038] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The medial superior olive (MSO) is a key auditory brainstem structure that receives binaural inputs and is implicated in processing interaural time disparities used for sound localization. The deaf white cat, a proven model of congenital deafness, was used to examine how deafness and cochlear implantation affected the synaptic organization at this binaural center in the ascending auditory pathway. The patterns of axosomatic and axodendritic organization were determined for principal neurons from the MSO of hearing, deaf, and deaf cats with cochlear implants. The nature of the synapses was evaluated through electron microscopy, ultrastructure analysis of the synaptic vesicles, and immunohistochemistry. The results show that the proportion of inhibitory axosomatic terminals was significantly smaller in deaf animals when compared with hearing animals. However, after a period of electrical stimulation via cochlear implants the proportion of inhibitory inputs resembled that of hearing animals. Additionally, the excitatory axodendritic boutons of hearing cats were found to be significantly larger than those of deaf cats. Boutons of stimulated cats were significantly larger than the boutons in deaf cats, although not as large as in the hearing cats, indicating a partial recovery of excitatory inputs to MSO dendrites after stimulation. These results exemplify dynamic plasticity in the auditory brainstem and reveal that electrical stimulation through cochlear implants has a restorative effect on synaptic organization in the MSO.
Collapse
Affiliation(s)
- Natasha N Tirko
- Department of Biomedical Engineering, Center for Hearing and Balance, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | | |
Collapse
|
27
|
|
28
|
O’Neil JN, Connelly CJ, Limb CJ, Ryugo DK. Synaptic morphology and the influence of auditory experience. Hear Res 2011; 279:118-30. [PMID: 21310226 PMCID: PMC3116016 DOI: 10.1016/j.heares.2011.01.019] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 01/26/2011] [Accepted: 01/29/2011] [Indexed: 11/27/2022]
Abstract
The auditory experience is crucial for the normal development and maturation of brain structure and the maintenance of the auditory pathways. The specific aims of this review are (i) to provide a brief background of the synaptic morphology of the endbulb of Held in hearing and deaf animals; (ii) to argue the importance of this large synaptic ending in linking neural activity along ascending pathways to environmental acoustic events; (iii) to describe how the re-introduction of electrical activity changes this synapse; and (iv) to examine how changes at the endbulb synapse initiate trans-synaptic changes in ascending auditory projections to the superior olivary complex, the inferior complex, and the auditory cortex.
Collapse
Affiliation(s)
- Jahn N. O’Neil
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Catherine J. Connelly
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Charles J. Limb
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - David K. Ryugo
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
- Program in Neuroscience, Garvan Institute of Medical Research, Darlinghurst, NSW 2010, Australia
| |
Collapse
|
29
|
Nayagam BA, Muniak MA, Ryugo DK. The spiral ganglion: connecting the peripheral and central auditory systems. Hear Res 2011; 278:2-20. [PMID: 21530629 PMCID: PMC3152679 DOI: 10.1016/j.heares.2011.04.003] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 03/26/2011] [Accepted: 04/03/2011] [Indexed: 12/15/2022]
Abstract
In mammals, the initial bridge between the physical world of sound and perception of that sound is established by neurons of the spiral ganglion. The cell bodies of these neurons give rise to peripheral processes that contact acoustic receptors in the organ of Corti, and the central processes collect together to form the auditory nerve that projects into the brain. In order to better understand hearing at this initial stage, we need to know the following about spiral ganglion neurons: (1) their cell biology including cytoplasmic, cytoskeletal, and membrane properties, (2) their peripheral and central connections including synaptic structure; (3) the nature of their neural signaling; and (4) their capacity for plasticity and rehabilitation. In this report, we will update the progress on these topics and indicate important issues still awaiting resolution.
Collapse
Affiliation(s)
- Bryony A Nayagam
- Department of Otolaryngology, University of Melbourne, Melbourne, VIC Australia
| | - Michael A Muniak
- Department of Neuroscience, Johns Hopkins University, Baltimore, MD USA
| | - David K Ryugo
- Department of Neuroscience, Johns Hopkins University, Baltimore, MD USA
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University, Baltimore, MD USA
- Garvan Institute, Darlinghurst, NSW Australia
| |
Collapse
|
30
|
Chen I, Limb CJ, Ryugo DK. The effect of cochlear-implant-mediated electrical stimulation on spiral ganglion cells in congenitally deaf white cats. J Assoc Res Otolaryngol 2010; 11:587-603. [PMID: 20821032 PMCID: PMC2975880 DOI: 10.1007/s10162-010-0234-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Accepted: 08/13/2010] [Indexed: 10/19/2022] Open
Abstract
It has long been observed that loss of auditory receptor cells is associated with the progressive degeneration of spiral ganglion cells. Chronic electrical stimulation via cochlear implantation has been used in an attempt to slow the rate of degeneration in cats neonatally deafened by ototoxic agents but with mixed results. The present study examined this issue using white cats with a history of hereditary deafness as an alternative animal model. Nineteen cats provided new data for this study: four normal-hearing cats, seven congenitally deaf white cats, and eight congenitally deaf white cats with unilateral cochlear implants. Data from additional cats were collected from the literature. Electrical stimulation began at 3 to 4 or 6 to 7 months after birth, and cats received stimulation for approximately 7 h a day, 5 days a week for 12 weeks. Quantitative analysis of spiral ganglion cell counts, cell density, and cell body size showed no marked improvement between cochlear-implanted and congenitally deaf subjects. Average ganglion cell size from cochlear-implanted and congenitally deaf cats was statistically similar and smaller than that of normal-hearing cats. Cell density from cats with cochlear implants tended to decrease within the upper basal and middle cochlear turns in comparison to congenitally deaf cats but remained at congenitally deaf levels within the lower basal and apical cochlear turns. These results provide no evidence that chronic electrical stimulation enhances spiral ganglion cell survival, cell density, or cell size compared to that of unstimulated congenitally deaf cats. Regardless of ganglion neuron status, there is unambiguous restoration of auditory nerve synapses in the cochlear nucleus of these cats implanted at the earlier age.
Collapse
Affiliation(s)
- Iris Chen
- Department of Otolaryngology-HNS, Center for Hearing and Balance, Johns Hopkins University School of Medicine, Traylor 510, 720 Rutland Ave, Baltimore, MD 21205 USA
| | - Charles J. Limb
- Department of Otolaryngology-HNS, Center for Hearing and Balance, Johns Hopkins University School of Medicine, Traylor 510, 720 Rutland Ave, Baltimore, MD 21205 USA
| | - David K. Ryugo
- Department of Otolaryngology-HNS, Center for Hearing and Balance, Johns Hopkins University School of Medicine, Traylor 510, 720 Rutland Ave, Baltimore, MD 21205 USA
- Department of Neuroscience, Center for Hearing and Balance, Johns Hopkins University School of Medicine, Baltimore, MD 21205 USA
- Garvan Institute of Medical Research, Darlinghurst, Sydney, NSW 2010 Australia
| |
Collapse
|
31
|
Baker CA, Montey KL, Pongstaporn T, Ryugo DK. Postnatal development of the endbulb of held in congenitally deaf cats. Front Neuroanat 2010; 4:19. [PMID: 20640179 PMCID: PMC2904654 DOI: 10.3389/fnana.2010.00019] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Accepted: 04/24/2010] [Indexed: 11/13/2022] Open
Abstract
The endbulbs of Held are formed by the ascending branches of myelinated auditory nerve fibers and represent one of the largest synaptic endings in the brain. Normally, these endings are highly branched and each can form up to 1000 dome-shaped synapses. The deaf white cat is a model of congenital deafness involving a type of cochleosaccular degeneration that mimics the Scheibe deformity in humans. Endbulbs of mature deaf white cats exhibit reduced branching, hypertrophy of postsynaptic densities (PSDs), and changes in synaptic vesicle density. Because cats are essentially deaf at birth, we sought to determine if the progression of brain abnormalities was linked in time to the failure of normal hearing development. The rationale was that the lack of sound-evoked activity would trigger pathologic change in deaf kittens. The cochleae of deaf cats did not exhibit abnormal morphology at birth. After the first postnatal week, however, the presence of a collapsed scala media signaled the difference between deaf and hearing cats. By working backwards in age, endbulbs of deaf cats expressed flattened and elongated PSDs and increased synaptic vesicle density as compared to normal endbulbs. These differences are present at birth in some white kittens, presaging deafness despite their normal cochlear histology. We speculate that hearing pathology is signaled by a perinatal loss of spontaneous bursting activity in auditory nerve fibers or perhaps by some factor released by hair cell synapses before obliteration of the organ of Corti.
Collapse
Affiliation(s)
- Christa A Baker
- Department of Otolaryngology, Johns Hopkins University Baltimore, MD, USA
| | | | | | | |
Collapse
|