Clinical differentiation of conductive hearing loss

Stroud, Malcolm H.

doi:10.1288/00005537-197808000-00002

Cited by 360 publications

(228 citation statements)

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“…Thus, these animals have no normal auditory experience and model congenital bilateral profound hearing loss. Hair cell degeneration in these animals leads to subsequent degeneration of the primary afferent cochlear spiral ganglion (SG) neurons and their central axons that form the auditory nerve, as in virtually all deafness etiologies in humans, (Hawkins et al, 1977;Johnson et al, 1981;Nadol, 1981;Otte et al, 1978;Ylikoski, 1974). Initial SG cell degeneration is evident by 2-3 weeks postnatal (Leake et al, 1997) and is progressive and continues for many months to years (Leake and Hradek,'88).…”

Section: Data From Animal Models Suggest Two Phases In Spiral Gangliomentioning

confidence: 99%

Factors influencing neurotrophic effects of electrical stimulation in the deafened developing auditory system

et al. 2008

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Research in animal models has demonstrated that electrical stimulation from a cochlear implant (CI) may help prevent degeneration of the cochlear spiral ganglion (SG) neurons after deafness. In cats deafened early in life, effective stimulation of the auditory nerve with complex signals for several months preserved a greater density of SG neurons in the stimulated cochleae as compared to the contralateral deafened ear. However, SG survival was still far from normal even with early intervention with an implant. Thus, pharmacologic agents and neurotrophic factors that might be used in combination with an implant are of great interest. Exogenous administration of GM1 ganglioside significantly reduces SG degeneration in deafened animals studied at 7-8 weeks of age, but after several months of stimulation, GM1-treated animals show only modestly better preservation of SG density compared to age-matched non-treated animals. A significant factor influencing neurotrophic effects in animal models is insertion trauma, which results in significant regional SG degeneration. Thus, an important goal is to further improve human CI electrode designs and insertion techniques to minimize trauma.Another important issue for studies of neurotrophic effects in the developing auditory system is the potential role of critical periods. Studies examining animals deafened at 30 days of age (rather than at birth) have explored whether a brief initial period of normal auditory experience affects the vulnerability of the SG or cochlear nucleus (CN) to auditory deprivation. Interestingly, SG survival in animals deafened at 30-days was not significantly different from age-matched neonatally deafened animals, but significant differences were observed in the central auditory system. CN volume was significantly closer to normal in the animals deafened at 30 days as compared to neonatally deafened animals. However, no difference was observed between the stimulated and contralateral CN volumes in either deafened group. Measurements of AVCN spherical cell somata showed that after later onset of deafness in the 30-day deafened group, mean cell size was significantly closer to normal than in the neonatally deafened group. Further, electrical stimulation elicited a significant increase in spherical cell size in the CN ipsilateral to the implant as compared to the contralateral CN in both deafened groups.Neuronal tracer studies have examined the primary afferent projections from the SG to the CN in neonatally deafened cats. CN projections exhibit a clear cochleotopic organization despite severe auditory deprivation from birth. However, when normalized for the smaller CN size after deafness, projections were 30-50% broader than normal. After unilateral electrical stimulation there was no difference between projections from the stimulated and non-stimulated ears. These findings suggest that early normal auditory experience may be essential for the normal development (or subsequent Publisher's Disclaimer: This is a PDF file of an unedited manuscript...

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Section: Data From Animal Models Suggest Two Phases In Spiral Gangliomentioning

confidence: 99%

Factors influencing neurotrophic effects of electrical stimulation in the deafened developing auditory system

et al. 2008

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“…Given that the larger numbers of channels available with the latest CI technology (e.g., Bvirtual channels^) may allow more flexibility in the frequency ranges delivered to different cochlear regions, further improvement of CI performance may depend on optimizing the tonotopic mapping of individual channels relative to the actual position of stimulation sites in the cochlea. A number of recent studies have been directed toward providing a better understanding of the role of electrode location and spacing on various perceptual attributes of hearing with a CI (Blamey et al 1996;Ketten et al 1998;Pfingst et al 2001;Skinner et al 2002;Yukawa et al 2004;Baumann and Nobbe 2006;Boex et al 2006). Several psychophysical studies have shown that spectral distortions such as apical or basal shift (Dorman et al 1997;Fu and Shannon 1999), nonlinear warping (Shannon et al 1998), and compression or expansion of the applied frequency map Shannon 2003, 2004) decrease speech perception, thus suggesting that an optimum fit of the frequency map for a given electrode position may significantly improve the performance of the CI listener.…”

Section: Introductionmentioning

confidence: 99%

“…A potentially important consideration is that Greenwood_s equation may provide an accurate estimate of frequency for CI electrodes only if the site of spike initiation in electrical excitation of the spiral ganglion (SG) neurons is near the OC, i.e., at the first node of Ranvier on the radial nerve fibers. However, radial nerve fibers begin to degenerate soon after the OC is damaged (Otte et al 1978;Hinojosa et al 1983; Leake and Hradek 1988;Nadol et al 1989;Nadol 1990;McFadden et al 2004). In contrast, SG cell somata degenerate relatively slowly in humans, and significant populations often survive even after decades of deafness, and/or after many years of CI use, even when radial nerve fibers are largely absent (Fayad et al 1991;Nadol 1997;Khan et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Frequency Map for the Human Cochlear Spiral Ganglion: Implications for Cochlear Implants

Stakhovskaya

Sridhar

Bonham

et al. 2007

JARO

356

357

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The goals of this study were to derive a frequencyposition function for the human cochlear spiral ganglion (SG) to correlate represented frequency along the organ of Corti (OC) to location along the SG, to determine the range of individual variability, and to calculate an Baverage^frequency map (based on the trajectories of the dendrites of the SG cells). For both OC and SG frequency maps, a potentially important limitation is that accurate estimates of cochlear place frequency based upon the Greenwood function require knowledge of the total OC or SG length, which cannot be determined in most temporal bone and imaging studies. Therefore, an additional goal of this study was to evaluate a simple metric, basal coil diameter that might be utilized to estimate OC and SG length. Cadaver cochleae (n = 9) were fixed G24 h postmortem, stained with osmium tetroxide, microdissected, decalcified briefly, embedded in epoxy resin, and examined in surface preparations. In digital images, the OC and SG were measured, and the radial nerve fiber trajectories were traced to define a series of frequency-matched coordinates along the two structures. Images of the cochlear turns were reconstructed and measurements of basal turn diameter were made and correlated with OC and SG measurements. The data obtained provide a mathematical function for relating represented frequency along the OC to that of the SG.Results showed that whereas the distance along the OC that corresponds to a critical bandwidth is assumed to be constant throughout the cochlea, estimated critical band distance in the SG varies significantly along the spiral. Additional findings suggest that measurements of basal coil diameter in preoperative images may allow prediction of OC/SG length and estimation of the insertion depth required to reach specific angles of rotation and frequencies. Results also indicate that OC and SG percentage length expressed as a function of rotation angle from the round window is fairly constant across subjects. The implications of these findings for the design and surgical insertion of cochlear implants are discussed.

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“…Open-set speech recognition is a key indicator of clinical success for humans who have received cochlear implants. Variables that influence implant outcomes include duration of deafness, cause of deafness, and ganglion cell survival (Otte et al 1978;Nadol et al 1989;Moore et al 1997;Linthicum and Fayad 2009). Other possible peripheral variables that are more difficult to assess are degree of auditory nerve fiber myelination, peripheral process survival, proximity of electrodes to primary neurons, amount of scar tissue resulting from surgical trauma and implantation, and blood supply to primary neurons.…”

Section: Figmentioning

confidence: 99%

“…Yet the exact contribution of the total number of spiral ganglion cells to auditory performance remains unclear (Otte et al 1978;Fayad and Linthicum 2006). In light of the fact that more than 120,000 individuals worldwide have received cochlear implants for the treatment of profound sensorineural hearing impairment (Wilson and Dorman 2008), clarification of the relationship between electrical stimulation of the cochlea and spiral ganglion cell viability is of paramount significance.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Cochlear-Implant-Mediated Electrical Stimulation on Spiral Ganglion Cells in Congenitally Deaf White Cats

Chen

Limb

Ryugo

2010

JARO

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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.

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Clinical differentiation of conductive hearing loss

Cited by 360 publications

References 0 publications

Factors influencing neurotrophic effects of electrical stimulation in the deafened developing auditory system

Factors influencing neurotrophic effects of electrical stimulation in the deafened developing auditory system

Frequency Map for the Human Cochlear Spiral Ganglion: Implications for Cochlear Implants

The Effect of Cochlear-Implant-Mediated Electrical Stimulation on Spiral Ganglion Cells in Congenitally Deaf White Cats

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