Histopathology of human cochlear implants: Correlation of psychophysical and anatomical measures

Khan, Aayesha M.; Whiten, Darren M.; Nadol, Joseph B.; Eddington, Donald K.

doi:10.1016/j.heares.2005.03.003

Cited by 52 publications

(42 citation statements)

References 40 publications

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“…It is particularly interesting to note that the correlation between neural density and electrophysiological thresholds is improved if we estimate the SG density in the region near the stimulating electrodes, rather than the overall SG density averaged for the entire cochlea ( Fig. 3a,b), similar to the findings by Khan et al (2005b) in human temporal bone studies.…”

Section: Functional Significance Of Sg Neuron Survivalsupporting

confidence: 76%

“…to determine CI performance. In fact, more detailed analyses using 2D reconstructions to evaluate the number of surviving SG cells in the regions near individual electrodes (Khan et al, 2005b) have reported significant correlations between psychophysical measures (last threshold and maximum comfortable loudness levels for individual electrodes) and SG counts in 2 of 5 subjects. These authors suggest that 3D reconstruction techniques will be required to fully assess the impact of peripheral anatomy on patient performance.…”

Section: Functional Significance Of Sg Neuron Survivalmentioning

confidence: 99%

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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: Functional Significance Of Sg Neuron Survivalsupporting

confidence: 76%

Section: Functional Significance Of Sg Neuron Survivalmentioning

confidence: 99%

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

et al. 2008

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“…Although conventional 2-D reconstruction of the cochlea provides valuable information, 3-D reconstruction provides additional data [Kahn et al, 2005]. In addition, as demonstrated in the present study, it facilitates a quantitative evaluation of histological changes within the cochlea.…”

Section: -D Reconstructionmentioning

confidence: 67%

Quantitative Evaluation of New Bone and Fibrous Tissue in the Cochlea following Cochlear Implantation in the Human

et al. 2007

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The formation of new bone and fibrous tissue in the human inner ear following cochlear implantation was evaluated by computer-assisted 3-D reconstruction. Seven temporal bones from patients who in life had undergone cochlear implantation were prepared for histological study with the implant in situ. The specimens were sectioned in the axial plane at a thickness of 20 µm. At least every tenth section was digitally reconstructed in three dimensions and volumes of new bone and fibrous tissue were calculated per millimeter length of the cochlea. New bone and fibrous tissue were found in all seven specimens, particularly at the cochleostomy site. In addition, new bone and fibrous tissue had extended to variable lengths along the track of the cochlear implant and in some cases extended beyond the distal end of the implanted electrode. This methodology provides a quantitative tool for evaluation of new bone and fibrous tissue in the inner ear following implantation. This should assist in correlating psychophysical and speech perception tests with intracochlear pathology, evaluating both electrode design and the techniques of preserving residual auditory function.

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“…Although there is no clear evidence that the degree of SGC degeneration is a predictor of speech perception (e.g., Fayad and Linthicum 2006;Khan et al 2005a,b), it is generally assumed that SGC survival plays a critical role for word recognition, especially if the number of SGCs is very low (Clopton et al 1980;Incesulu and Nadol 1998;Khan et al 2005b;Nadol 1984;Nadol et al 1989;Otte et al 1978). However, many other variables, especially including alterations in the central auditory pathway and its signal processing capacity, likely play important roles in the success of cochlear implantation.…”

Section: Cochlear Pathologymentioning

confidence: 99%

Spatial Selectivity to Intracochlear Electrical Stimulation in the Inferior Colliculus is Degraded After Long-Term Deafness in Cats

Vollmer¹,

Beitel²,

Snyder³

et al. 2007

Journal of Neurophysiology

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Vollmer M, Beitel RE, Snyder RL, Leake PA. Spatial selectivity to intracochlear electrical stimulation in the inferior colliculus is degraded after long-term deafness in cats. J Neurophysiol 98: 2588 -2603, 2007. First published September 12, 2007 doi:10.1152/jn.00011.2007. In an animal model of electrical hearing in prelingually deaf adults, this study examined the effects of deafness duration on response thresholds and spatial selectivity (i.e., cochleotopic organization, spatial tuning and dynamic range) in the central auditory system to intracochlear electrical stimulation. Electrically evoked auditory brain stem response (EABR) thresholds and neural response thresholds in the external (ICX) and central (ICC) nuclei of the inferior colliculus were estimated in cats after varying durations of neonatally induced deafness: in animals deafened Ͻ1.5 yr (short-deafened unstimulated, SDU cats) with a mean spiral ganglion cell (SGC) density of ϳ45% of normal and in animals deafened Ͼ2.5 yr (long-deafened, LD cats) with severe cochlear pathology (mean SGC density Ͻ7% of normal). LD animals were subdivided into unstimulated cats and those that received chronic intracochlear electrical stimulation via a feline cochlear implant. Acutely deafened, implanted adult cats served as controls. Independent of their stimulation history, LD animals had significantly higher EABR and ICC thresholds than SDU and control animals. Moreover, the spread of electrical excitation was significantly broader and the dynamic range significantly reduced in LD animals. Despite the prolonged durations of deafness the fundamental cochleotopic organization was maintained in both the ICX and the ICC of LD animals. There was no difference between SDU and control cats in any of the response properties tested. These findings suggest that long-term auditory deprivation results in a significant and possibly irreversible degradation of response thresholds and spatial selectivity to intracochlear electrical stimulation in the auditory midbrain.

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Histopathology of human cochlear implants: Correlation of psychophysical and anatomical measures

Cited by 52 publications

References 40 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

Quantitative Evaluation of New Bone and Fibrous Tissue in the Cochlea following Cochlear Implantation in the Human

Spatial Selectivity to Intracochlear Electrical Stimulation in the Inferior Colliculus is Degraded After Long-Term Deafness in Cats

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