Graeme Clark Collection
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ItemHistological and physiological effects of the central auditory prosthesis: surface versus penetrating electrodes( 1997)Unavailable due to copyright.
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ItemDoes age at cochlear implantation affect the distribution of 2-deoxyglucose label in cat inferior colliculus?( 1996)Cochlear implants are one treatment for children who are born deaf or become deaf before acquiring language. The question of optimum age for implantation arises. Using an animal model, we have studied the response of the auditory brainstem to implantation at various ages. Neonatally, pharmacologically deafened cats were implanted with a 4-electrode array in the left cochlea at ages from 100 to over 180 days. Eleven were chronically stimulated (1000 h if possible) with charge-balanced, biphasic current pulses: eight were unstimulated controls. In a terminal experiment, each animal received [^14C]2-deoxyglucose i.v. preceding a 45-min stimulation program. The fraction of the right inferior colliculus (IC) with a significant accumulation of label was calculated. If age at implantation were a significant factor in determining the size of the responding region, the fraction would depend on the age: this was not observed. However, there was considerable variation in the IC fraction sizes within both stimulated and unstimulated groups, leading to the conclusion that there are factors other than age which determine the size of the responding region. Thus, for deaf children of corresponding ages, age at implantation may not be of critical importance.
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ItemComparison of monaural acoustic and electric stimulation: unit types in the cat inferior colliculus( 1995)This study has shown that 1) the ratio of excitatory and inhibitory inputs to units in the central nucleus of the inferior colliculus is altered when one cochlea is neomycin-deafened and/or electrically stimulated; 2) prestimulus threshold shift and lateral inhibition mechanisms can be used to explain these results; and 3) at high current levels a leakage current into the modiolus can evoke unit population responses.
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ItemExperimental animal model of intracochlear ossification in relation to cochlear implantation( 1995)Histopathologic examinations of the temporal bones of implanted human patients and experimental animals have demonstrated various degrees of abnormal fibrous tissue or new bone formation within the cochlea; in some cases, extensive new bone formation was reported. The presence of new bone following cochlear implantation is undesirable, since it may adversely affect current distributions in the electrically stimulated cochlea. The pathogenesis of intracochlear osteoneogenesis as a direct result of cochlear implantation is unclear. The aim of this study is to use an experimental animal model to investigate some of the factors underlying the formation of new bone and fibrous tissue within the implanted cochlea, especially the role of insertion trauma and bone chips, and also a possible way of inhibiting such a process using an anticalcific agent of the diphosphonate family, disodium ethane-1-hydroxy-1, 1-diphosphonate(EHDP). The local release of EHDP from a polydimethylsiloxane (Silastic silicone rubber, Dow Corning Corp) controlled delivery system has been shown effective in the context of bioprosthetic heart valve. Its application within the cochlea has not been documented, to our knowledge.
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ItemDischarge rate-level functions from dorsal cochlear nucleus single units in response to acoustic and electrical stimulation of the auditory nerve( 1995)Discharge rate-level (I/O) functions possessed by dorsal cochlear nucleus (DCN) units were examined, in response to bipolar electrical stimulation of the cochlea of the barbiturate-anesthetized cat. Spontaneously active units usually possessed nonmonotonic functions with a minimum, and spontaneously inactive units usually possessed monotonic functions or nonmonotonic functions with a maximum (NM+). In response to acoustic high-pass filtered noise, the function relating discharge rate and cut off frequency resembled the same unit's I/O function to electrical stimulation. The I/O functions to acoustic characteristic tones were usually monotonic or NM+. These results suggest that in the DCN, a prerequisite for the generation of acoustic-like responses with an electrical stimulus may be the matching of the cochlear place and spatial extent activated by each stimulus.
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ItemCochlear implants in children: the value of cochleostomy seals in the prevention of labyrinthitis following pneumococcal otitis media( 1995)Cochlea implantation at an early age is important in rehabilitating profoundly hearing impaired children. Given the incidence of pneumococcal otitis media in young children, there has been concern that cochlear implantation could increase the possibility of otitis media, leading to labyrinthitis in this age group. Clinical experience has not indicated an increase in the frequency of otitis media and labyrinthitis in implanted adults or children over two years. However, labyrinthitis has occurred in implanted animals with otitis media. In order to assess the impact of cochlear implants on the occurrence of labyrinthitis, pneumococcal otitis media was induced in 21 kittens. Thirty-two kitten cochleas were implanted, of which 9 had a fascial graft and 9 a Gelfoam® graft. Nine control cochleas were unimplanted. Labyrinthitis occurred in 44% of unimplanted controls. 50% of implanted ungrafted cochleas, and 6% of implanted grafted cochleas. There was no statistically significant difference between the incidence of labyrinthitis in the implanted cochleas and the unimplanted controls. However there was a statistically significant difference between the ungrafted and grafted cochleas, but not between the two types of graft.