Graeme Clark Collection
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ItemA physiological investigation of chronic electrical stimulation with scala tympani electrodes in kittens( 1992)A physiological investigation of cochlear electrical stimulation was undertaken in six two-month-old kittens. The scala tympani electrodes were implanted and electrically stimulated using biphasic balanced electrical pulses' for periods of 1000-1500h in four ears. Four ears received implants for same period but without electrical stimulation. The other two ears served as normal control. The results indicated: 1) Chronic electrical stimulation of the cochlea within electrochemically safe limits did not influence the hearing of kittens and the normal delivery of impulses evoked by acoustic and electrical signals on the auditory brainstem pathway. 2) The wave shapes of EABRs were similar to those of ABRs. The aptitudes of EABRs showed a significant increase following chronic electrical stimulation, resulting in a leftward shift in the input/ output function. The absolute latencies and interwave latencies of waves II-III , III -IV and II -IV were significantly shorter than those of ABRs. These results imply that there was no adverse effect of chronic electrical stimulation on the maturing auditory systems of kittens using these electrical parameters and the mechanism of electrical hearing should be further studied.
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ItemExperimental study on extracochlear electric stimulation [Abstract]( 1992)The efficiency and feasibility of chronic extracochlear implantation and electric stimulation were studied in two adult cats and four 2-month kittens. The first electrode was placed on the round window by fixing the leadwire on the bridge of aditus between the middle ear and bulla cavity; the second electrode was placed on the surface of the tympanic promontory; the third was inserted into the temporal muscle out of the bulla and the forth fixed in transverse sinus with dental cement. ABRs and EABRs were recorded pre-and postoperatively and during electric stimulation.
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ItemCochlear implantation in young children: studies on head growth, leadwire design and electrode fixation in the monkey model [Abstract]( 1992)For the safety of cochlear implantation in children under two, the implant assembly must not adversely effect the tissue of compromise head growth. Furthermore, growth changes and tissue responses should not impair functioning of the device. Dummy receiver-stimulators, interconnect plugs and leadwire-lengthening systems have been implanted for periods of 40 months in the young monkey to most effectively model the implantation of the young human child. The results show that implanting a receiver-stimulator package has no effect on skull growth or brain tissue under the package. The system for fixing the electrode at the fossa includes proved effective. There was marked osteoneogenesis in the mastoid cavity and this also resulted in fixation of the leadwire outside the cochlea. This study provides evidence for the safety of cochlear implantation in young children.
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ItemCochlear implantation in young children: long-term effects of implantation on the skull and underlying central nervous system tissues in a primate model [Abstract]( 1992)Recent independent studies reporting results obtained by profoundly deaf children implanted with the Melbourne 22-channel cochlear implant have provided further impetus for assessing the feasibility of implanting children under two. Studies in appropriate animal models must first establish the safety of this procedure.
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ItemCochlear implantation in young children: long-term effects of implantation on normal hair cells and spiral ganglion cells in the monkey model [Abstract]( 1992)Recent independent results obtained by profoundly deaf children implanted with the Melbourne 22-channel cochlear implant (1) have provided further impetus. for examining thefeasibility of implanting children under two and children with profound deafness. Safety st1,ldies, in appropriate animal models, must first establish the safety of this procedure.
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ItemElectrical stimulation of the auditory nerve in deaf kittens: effects on cochlear nuclei [Abstract]( 1990)Acoustic experience plays an important role in the development of the auditory system. Neonatal sound deprivation will result in significant reduction of both the cell soma area and total volume of the ventral cochlear nuclei (VCN) in adult animals (Webster, 1988). The present study has been undertaken to investigate this phenomenon by examining the effects of electrical stimulation of the auditory nerve of the kitten, on the morphology of the cochlear nucleus in animals deprived of sound following the administration of ototoxic drugs.
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ItemClinical results for children using the 22-channel cochlear prosthesis [Abstract]( 1991)Twenty five profoundly/totally hearing-impaired children aged between 2 and 18 years have been implanted with the 22-channel cochlear prosthesis (Cochlear Pty. Ltd.) at The University of Melbourne over the last five years. Speech perception, speech production and language development have been monitored for these children both pre- and postoperatively. Results have shown improvements for all children in speech perception, postoperatively. The younger children (< 12 years) and those with an acquired (postlinguistic) profound hearing loss, have demonstrated some open-set speech recognition without visual clues. In general, older children with a prelinguistic profound hearing loss have not attained this level of performance. Improvements in speech production and language have also been demonstrated and tend to occur faster in younger children. Importantly, a number of congenitally deaf young children have shown significant improvements in speech perception, production and language. Important factors in the success of cochlear implants in children appear to be: educational environment - it is vital to have a strong auditory component (i.e. non-signing); careful attention to correct programming and maintenance of the prosthesis; support of family and other professionals.