The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
David K Ryugo - One of the best experts on this subject based on the ideXlab platform.
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descending projections from the inferior colliculus to medial olivocochlear efferents mice with normal hearing early onset hearing loss and Congenital Deafness
Hearing Research, 2017Co-Authors: Kirupa Suthakar, David K RyugoAbstract:Auditory efferent neurons reside in the brain and innervate the sensory hair cells of the cochlea to modulate incoming acoustic signals. Two groups of efferents have been described in mouse and this report will focus on the medial olivocochlear (MOC) system. Electrophysiological data suggest the MOC efferents function in selective listening by differentially attenuating auditory nerve fiber activity in quiet and noisy conditions. Because speech understanding in noise is impaired in age-related hearing loss, we asked whether pathologic changes in input to MOC neurons from higher centers could be involved. The present study investigated the anatomical nature of descending projections from the inferior colliculus (IC) to MOCs in 3-month old mice with normal hearing, and in 6-month old mice with normal hearing (CBA/CaH), early onset progressive hearing loss (DBA/2), and Congenital Deafness (homozygous Shaker-2). Anterograde tracers were injected into the IC and retrograde tracers into the cochlea. Electron microscopic analysis of double-labelled tissue confirmed direct synaptic contact from the IC onto MOCs in all cohorts. These labelled terminals are indicative of excitatory neurotransmission because they contain round synaptic vesicles, exhibit asymmetric membrane specializations, and are co-labelled with antibodies against VGlut2, a glutamate transporter. 3D reconstructions of the terminal fields indicate that in normal hearing mice, descending projections from the IC are arranged tonotopically with low frequencies projecting laterally and progressively higher frequencies projecting more medially. Along the mediolateral axis, the projections of DBA/2 mice with acquired high frequency hearing loss were shifted medially towards expected higher frequency projecting regions. Shaker-2 mice with Congenital Deafness had a much broader spatial projection, revealing abnormalities in the topography of connections. These data suggest that loss in precision of IC directed MOC activation could contribute to impaired signal detection in noise.
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Bilateral effects of unilateral cochlear implantation in Congenitally deaf cats.
The Journal of Comparative Neurology, 2010Co-Authors: Jahn N. O’neil, Charles J. Limb, Christa A. Baker, David K RyugoAbstract:Congenital Deafness results in synaptic abnormalities in auditory nerve endings. These abnormalities are most prominent in terminals called endbulbs of Held, which are large, axosomatic synaptic endings whose size and evolutionary conservation emphasize their importance. Transmission jitter, delay, or failures, which would corrupt the processing of timing information, are possible consequences of the perturbations at this synaptic junction. We sought to determine whether electrical stimulation of the Congenitally deaf auditory system via cochlear implants would restore the endbulb synapses to their normal morphology. Three and 6-month-old Congenitally deaf cats received unilateral cochlear implants and were stimulated for a period of 10–19 weeks by using human speech processors. Implanted cats exhibited acoustic startle responses and were trained to approach their food dish in response to a specific acoustic stimulus. Endbulb synapses were examined by using serial section electron microscopy from cohorts of cats with normal hearing, Congenital Deafness, or Congenital Deafness with a cochlear implant. Synapse restoration was evident in endbulb synapses on the stimulated side of cats implanted at 3 months of age but not at 6 months. In the young implanted cats, postsynaptic densities exhibited normal size, shape, and distribution, and synaptic vesicles had density values typical of hearing cats. Synapses of the contralateral auditory nerve in early implanted cats also exhibited synapses with more normal structural features. These results demonstrate that electrical stimulation with a cochlear implant can help preserve central auditory synapses through direct and indirect pathways in an age-dependent fashion. J. Comp. Neurol. 518:2382– 2404, 2010.
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the effects of Congenital Deafness on auditory nerve synapses and globular bushy cells in cats
Hearing Research, 2000Co-Authors: Elizabeth E Redd, Tan Pongstaporn, David K RyugoAbstract:It is well known that auditory deprivation affects the structure and function of the central nervous system. Congenital Deafness represents one form of deprivation, and in the adult white cat, it has been shown to have a clear effect upon the synaptic interface between endbulbs of Held and spherical bushy cells. It is not known, however, whether all primary synapses are affected and/or whether they are affected in the same way and to the same extent. Thus, we studied a second neuronal circuit in the deaf white cat involving modified (small) endbulbs and globular bushy cells. Compared to normal hearing cats, modified endbulbs of Congenitally deaf cats were 52.2% smaller but unchanged in structural complexity. There was also a striking loss of extracellular space between ending and cell body. The somata of postsynaptic globular bushy cells were 13.4% smaller and had enlarged postsynaptic densities. These data reveal that axosomatic synapses demonstrate abnormal structure as a consequence of Deafness and that the extent of the abnormalities can vary with respect to the circuits involved. The implication of these observations is that synaptic anomalies would introduce differential delays within separate circuits, thereby desynchronizing neural activity from sound stimuli. This loss of synchronization could in turn disrupt temporal processing and compromise a host of related functions, including language comprehension.
Andrej Kral - One of the best experts on this subject based on the ideXlab platform.
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Congenital Deafness reduces but does not eliminate auditory responsiveness in cat extrastriate visual cortex
Neuroscience, 2018Co-Authors: Rudiger Land, Janole Radecke, Andrej KralAbstract:Abstract Congenital Deafness not only affects the development of the auditory cortex, but also the interrelation between the visual and auditory system. For example, Congenital Deafness leads to visual modulation of the deaf auditory cortex in the form of cross-modal plasticity. Here we asked, whether Congenital Deafness additionally affects auditory modulation in the visual cortex. We demonstrate that auditory activity, which is normally present in the lateral suprasylvian visual areas in normal hearing cats, can also be elicited by electrical activation of the auditory system with cochlear implants. We then show that in adult Congenitally deaf cats auditory activity in this region was reduced when tested with cochlear implant stimulation. However, the change in this area was small and auditory activity was not completely abolished despite years of Congenital Deafness. The results document that Congenital Deafness leads not only to changes in the auditory cortex but also affects auditory modulation of visual areas. However, the results further show a persistence of fundamental cortical sensory functional organization despite Congenital Deafness.
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Congenital Deafness affects deep layers in primary and secondary auditory cortex
The Journal of Comparative Neurology, 2017Co-Authors: Christoph Berger, Verena Scheper, D. Kühne, Andrej KralAbstract: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 (DZ) 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 was 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. This article is protected by copyright. All rights reserved.
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higher order auditory areas in Congenital Deafness top down interactions and corticocortical decoupling
Hearing Research, 2017Co-Authors: Andrej Kral, Prasandhya Astagiri Yusuf, Rudiger LandAbstract:The theory of predictive coding assumes that higher-order representations influence lower-order representations by generating predictions about sensory input. In Congenital Deafness, one identified dysfunction is a reduced activation of deep layers in the auditory cortex. Since these layers play a central role for processing top-down influences, Congenital Deafness might interfere with the integration of top-down and bottom-up information flow. Studies in humans suggest more deficits in higher-order than in primary cortical areas in Congenital Deafness. That opens up the question how well neurons in higher-order areas can be activated by the input through the deprived auditory pathway after restoration of hearing with cochlear implants. Further it is unclear whether their interconnections to lower order areas are impaired by absence of hearing. Corticocortical anatomical fiber tracts and general auditory responsiveness in both primary and higher-order areas are generally preserved in absence of auditory experience. However, the existing data suggest a dichotomy between preservation of anatomical cortical connectivity in Congenital Deafness and functional deficits in corticocortical coupling. Further, cross-modal reorganization observed in Congenital Deafness in specific cortical areas appears to be established by functional synaptic changes and rests on anatomically preserved, genetically-predetermined and molecularly patterned circuitry connecting the sensory systems. Current data indicate a reduced corticocortical functional coupling between cortical auditory areas in Congenital Deafness, both in bottom-up and top-down information stream. Consequently, Congenital Deafness is likely to result in a deficit in predictive coding that affects learning ability after late cochlear implantation.
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monaural Congenital Deafness affects aural dominance and degrades binaural processing
Cerebral Cortex, 2016Co-Authors: Andrej Kral, Jochen Tillein, Peter HubkaAbstract: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.
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somatic memory and gain increase as preconditions for tinnitus insights from Congenital Deafness
Hearing Research, 2016Co-Authors: Jos J Eggermont, Andrej KralAbstract:Abstract Tinnitus is the conscious perception of sound heard in the absence of physical sound sources internal or external to the body. The characterization of tinnitus by its spectrum reflects the missing frequencies originally represented in the hearing loss, i.e., partially or completely deafferented, region. The tinnitus percept, despite a total hearing loss, may thus be dependent on the persisting existence of a somatic memory for the “lost” frequencies. Somatic memory in this context is the reference for phantom sensations attributed to missing sensory surfaces or parts thereof. This raises the question whether tinnitus can exist in Congenital Deafness, were somatic representations have not been formed. We review the development of tonotopic maps in altricial and precocial animals evidence for a lack of tinnitus in Congenital Deafness and the effects of cochlear implants on the formation of tonotopic maps in the Congenitally deaf. The latter relates to the emergence of tinnitus in these subjects. The reviewed material is consistent with the hypothesis that tinnitus requires an established and actively used somatotopic map that leads to a corresponding somatic memory. The absence of such experience explains the absence of tinnitus in Congenital bilateral and unilateral Deafness.
Jochen Tillein - One of the best experts on this subject based on the ideXlab platform.
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monaural Congenital Deafness affects aural dominance and degrades binaural processing
Cerebral Cortex, 2016Co-Authors: Andrej Kral, Jochen Tillein, Peter HubkaAbstract: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.
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cortical representation of interaural time difference in Congenital Deafness
Cerebral Cortex, 2010Co-Authors: Jochen Tillein, R Hartmann, Andreas K Engel, P Hubka, Emilie Syed, Andrej KralAbstract:Binaural cues are required for localization of sound sources. In the present paper, representation of binaural cues has been investigated in the adult auditory cortex. Hearing and Congenitally deaf cats were stimulated through binaural cochlear implants and unit responses were collected in the subregion of field A1 showing the largest amplitudes of evoked local field potentials. Sensitivity to interaural time difference (ITD) in the range from 2600 to 600 ms was tested at intensities of 0--10 dB above hearing threshold. Template ITD functions were fitted to the data and parameters of ITD functions were compared between deaf and hearing animals. In deaf animals, fewer units responded to binaural stimulation, and those that responded had smaller maximal evoked firing rate. The fit to the template ITD functions was significantly worse in deaf animals, and the modulation depth in ITD functions was smaller, demonstrating a decrease in ITD sensitivity. With increasing binaural levels, hearing controls demonstrated systematic changes in ITD functions not found in deaf animals. Bimodal responses, likely related to precedence effect, were rare in deaf animals. The data demonstrate that despite some rudimentary sensitivity to interaural timing, cortical representation of ITDs is substantially altered by Congenital auditory deprivation.
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spatiotemporal patterns of cortical activity with bilateral cochlear implants in Congenital Deafness
The Journal of Neuroscience, 2009Co-Authors: Andrej Kral, Jochen Tillein, Peter Hubka, Silvia Heid, Dorrit Schiemann, Rainer Hartmann, Andreas K EngelAbstract:Congenital Deafness affects developmental processes in the auditory cortex. In this study, local field potentials (LFPs) were mapped at the cortical surface with microelectrodes in response to cochlear implant stimulation. LFPs were compared between hearing controls and Congenitally deaf cats (CDCs). Pulsatile electrical stimulation initially evoked cortical activity in the rostral parts of the primary auditory field (A1). This progressed both in the approximate dorsoventral direction (along the isofrequency stripe) and in the rostrocaudal direction. The dorsal branch of the wavefront split into a caudal branch (propagating in A1) and another smaller one propagating rostrally into the AAF (anterior auditory field). After the front reached the caudal border of A1, a “reflection wave” appeared, propagating back rostrally. In total, the waves took ∼13–15 ms to propagate along A1 and return back. In CDCs, the propagation pattern was significantly disturbed, with a more synchronous activation of distant cortical regions. The maps obtained from contralateral and ipsilateral stimulation overlapped in both groups of animals. Although controls showed differences in the latency–amplitude patterns, cortical waves evoked by contralateral and ipsilateral stimulation were more similar in CDCs. Additionally, in controls, LFPs with contralateral and ipsilateral stimulation were more similar in caudal A1 than in rostral A1. This dichotomy was lost in deaf animals. In conclusion, propagating cortical waves are specific for the contralateral ear, they are affected by auditory deprivation, and the specificity of the cortex for stimulation of the contralateral ear is reduced by deprivation.
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hearing after Congenital Deafness central auditory plasticity and sensory deprivation
Cerebral Cortex, 2002Co-Authors: Andrej Kral, Jochen Tillein, R Hartmann, Silvia Heid, Rainer KlinkeAbstract:The Congenitally deaf cat suffers from a degeneration of the inner ear. The organ of Corti bears no hair cells, yet the auditory afferents are preserved. Since these animals have no auditory experience, they were used as a model for Congenital Deafness. Kittens were equipped with a cochlear implant at different ages and electrostimulated over a period of 2.0–5.5 months using a monopolar single-channel compressed analogue stimulation strategy (VIENNAtype signal processor). Following a period of auditory experience, we investigated cortical field potentials in response to electrical biphasic pulses applied by means of the cochlear implant. In comparison to naive unstimulated deaf cats and normal hearing cats, the chronically stimulated animals showed larger cortical regions producing middle-latency responses at or above 300 µV amplitude at the contralateral as well as the ipsilateral auditory cortex. The cortex ipsilateral to the chronically stimulated ear did not show any signs of reduced responsiveness when stimulating the ‘untrained’ ear through a second cochlear implant inserted in the final experiment. With comparable duration of auditory training, the activated cortical area was substantially smaller if implantation had been performed at an older age of 5–6 months. The data emphasize that young sensory systems in cats have a higher capacity for plasticity than older ones and that there is a sensitive period for the cat’s auditory system.
George M Strain - One of the best experts on this subject based on the ideXlab platform.
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Congenital Deafness in jack russell terriers prevalence and association with phenotype
Veterinary Journal, 2012Co-Authors: B Comito, K E Knowles, George M StrainAbstract:Congenital hereditary sensorineural Deafness is the most common form of Deafness in dogs. The objectives of this study were to determine a reliable measure of the prevalence of Deafness in Jack Russell terriers, an affected breed, and associations between Deafness and phenotypic characteristics. Brainstem auditory evoked response recordings and phenotypic parameters (coat color, coat texture, sex, eye color, sire and dam hearing status) were recorded for 1009 Jack Russell terriers. The prevalence of unilateral and bilateral Deafness was 3.57% and 0.50%, respectively, lower by a factor of three to four than in earlier reports based on smaller and closely related kindreds. Significant association with Deafness was identified with white coat color and parental hearing status, but not with sex or coat type. Lack of significant sex or coat type associations and the significant association with white coat color are consistent with previous reports. In conclusion the prevalence of Deafness in Jack Russell terriers is lower than initially reported. Deafness was associated with white coat color and parental hearing status. The association with parental hearing status supports this form of Deafness being a heritable trait in the breed and the association with white coat color supports an inheritance linked to pigmentation genes.
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Congenital Deafness and its recognition
Veterinary Clinics of North America-small Animal Practice, 1999Co-Authors: George M StrainAbstract:: Congenital Deafness in dogs and cats is primarily of the hereditary sensorineural form associated with white pigmentation genes, although acquired forms of Deafness are possible. Highest prevalence is seen in white cats, especially those with blue eyes, and the Dalmatian, with many other dog breeds affected to some extent. This Deafness results from degeneration of the cochlear blood supply at age 3-4 weeks, presumably resulting from suppression of melanocytes by the white (cat) or merle or piebald (dog) genes. Mechanism of inheritance is not understood for most breeds. Such animals should not be bred and may present liabilities for their owners. Objective diagnosis of Deafness, especially when unilateral, relies on the brainstem auditory evoked response, an electrodiagnostic test where electrical activity in response to a click stimulus is recorded from the scalp using needle electrodes and a special purpose computer. Client counseling guidelines are presented.
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brainstem auditory evoked potential assessment of Congenital Deafness in dalmatians associations with phenotypic markers
Journal of Veterinary Internal Medicine, 1992Co-Authors: George M Strain, Michael T Kearney, Ivan J Gignac, Donald Levesque, Holly J Nelson, Bruce L Tedford, Laura G RemsenAbstract:To screen for Congenital Deafness, brainstem auditory-evoked potential (BAEP) testing was performed on 1031 Dalmatians from three geographically separated areas. Phenotypic marker assessment was done to determine markers possibly associated with Deafness. Markers included sex, hair coat color, pigmentation of different areas of skin (eye rims, nose, and ears), presence of a patch, spot size and marking (density of spotting), sire and dam BAEP status, and presence of iris and retinal tapetal pigmentation. Combined data from all test sites showed 8.1 % bilateral Deafness (N = 83 dogs) and 21.60/0 unilateral Deafness (N = 223), or an overall 29.70/0 incidence of hearing disorders. Significant (P < 0.05) associations with Deafness for the data from all test sites combined were seen for patch, sire and dam BAEP, iris pigment, and retinal pigment. However, results differed for several of the significant pheno typic markers when analyses were done on the data from the individual test sites; changes from signifi cant to not significant were found. This suggested the existence of multiple populations of Deafness patterns, and reinforced the precautionary conclusion that associations of phenotypic markers with Deafness are not necessarily functionally significant. (Journal of Veterinary Internal Medicine 1992; 6:175-182)
Kirupa Suthakar - One of the best experts on this subject based on the ideXlab platform.
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descending projections from the inferior colliculus to medial olivocochlear efferents mice with normal hearing early onset hearing loss and Congenital Deafness
Hearing Research, 2017Co-Authors: Kirupa Suthakar, David K RyugoAbstract:Auditory efferent neurons reside in the brain and innervate the sensory hair cells of the cochlea to modulate incoming acoustic signals. Two groups of efferents have been described in mouse and this report will focus on the medial olivocochlear (MOC) system. Electrophysiological data suggest the MOC efferents function in selective listening by differentially attenuating auditory nerve fiber activity in quiet and noisy conditions. Because speech understanding in noise is impaired in age-related hearing loss, we asked whether pathologic changes in input to MOC neurons from higher centers could be involved. The present study investigated the anatomical nature of descending projections from the inferior colliculus (IC) to MOCs in 3-month old mice with normal hearing, and in 6-month old mice with normal hearing (CBA/CaH), early onset progressive hearing loss (DBA/2), and Congenital Deafness (homozygous Shaker-2). Anterograde tracers were injected into the IC and retrograde tracers into the cochlea. Electron microscopic analysis of double-labelled tissue confirmed direct synaptic contact from the IC onto MOCs in all cohorts. These labelled terminals are indicative of excitatory neurotransmission because they contain round synaptic vesicles, exhibit asymmetric membrane specializations, and are co-labelled with antibodies against VGlut2, a glutamate transporter. 3D reconstructions of the terminal fields indicate that in normal hearing mice, descending projections from the IC are arranged tonotopically with low frequencies projecting laterally and progressively higher frequencies projecting more medially. Along the mediolateral axis, the projections of DBA/2 mice with acquired high frequency hearing loss were shifted medially towards expected higher frequency projecting regions. Shaker-2 mice with Congenital Deafness had a much broader spatial projection, revealing abnormalities in the topography of connections. These data suggest that loss in precision of IC directed MOC activation could contribute to impaired signal detection in noise.