Graeme Clark Collection
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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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ItemRapid and permanent hearing loss in cats following co-administration of kanamycin and ethacrynic acid [Abstract]( 1990)A safe, simple and effective technique for producing profound-totally deaf animal models in both young and adult cats is required for auditory prosthesis related research. Exposure to loud noises can result in a partial hearing loss, the degree of which varies significantly among animals. Long-term systemic injection of an aminoglycoside ototoxic drug frequently results in renal dysfunction and can show significant variation in response among animals (Shepherd & Clark, 1985). Finally, direct infusion of ototoxic drugs produces extensive and highly variable cochlear pathology, unsuitable for auditory prosthesis research.
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ItemThe effect of position of the scala tympani electrode array on auditory nerve excitation [Abstract]( 1990)Multiple-channel auditory prostheses provide both temporal and formant information to profoundly-totally deaf patients. This is achieved via direct electrical stimulation of selective regions of the residual auditory nerve using an electrode array located in the scala tympani. Histological evidence has shown that these electrode arrays lie along the outer wall of the scala tympani, some distance from the residual nerve elements. In the present study we systematically varied the position of the electrode array within the cat scala tympani in order to investigate the influence of electrode position on neural excitation. Such knowledge may contribute to the development of improved electrode arrays for auditory prostheses.
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ItemVentral cochlear nucleus and auditory nerve fibre responses to electrical stimulation of the cat cochlea [Abstract]( 1987)Discharge patterns of cat auditory nerve fibres and ventral cochlear nucleus neurones to constant-current biphasic pulses have been recorded. The study was carried out to determine the input-output characteristics of the neurones, for variations in the rate and intensity of electrical stimulation. Neural discharges were highly synchronized with the current pulses at suprathreshold stimulus intensities, and saturation discharge rates usually equalled stimulus pulse rates up to 800 pulses/s. The electrically-driven discharge patterns of ventral cochlear nucleus neurones exhibiting "primary-like" responses were similar to those recorded from electrically-stimulated auditory nerve fibres. Comparison of the neural responses to electrical and acoustic stimulation may help in the design of improved speech processors for cochlear implants. Field potential responses were depressed at high stimulus rates and charge densities, suggesting stimulus-induced reduction in neural excitability. The effects of stimulus parameter variations on field potentials may help in determining safety limits of the electrical stimulus.
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ItemElectrical stimulation of the auditory nerve: effects of high stimulus rates [Abstract](Australian Physiological and Pharmacological Society, 1986)We have previously described non-damaging stimulus levels for chronic intracochlear electrical stimulation (Shepherd et al, 1983). However, maximum safe stimulus levels have yet to be clearly defined. Moreover, the importance of various stimulus parameters and their effects on the auditory nerve is not well understood. In the present study we have examined the effects of stimulus repetition rate on the auditory nerve by monitoring the Electrically-evoked Auditory Brainstem Response (EABR). Such information is necessary if speech processing strategies incorporating high pulse rates (i.e. > 300 pps) are to be made available to cochlear implant patients.
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ItemChronic electrical stimulation of the auditory nerve in cats( 1982)One requirement for the success of a cochlear hearing prosthesis is that long-term electrical stimulation must not have adverse effects on the residual spiral ganglion cell population. Electrochemically 'safe' stimulation regimes have been defined for the cortex (Brummer &Turner, 1977). However, few investigators have examined the effects of long-term intracochlear electrical stimulation. Walsh et al (1980), stimulating with current densities greater than the 'safe' limits defined by Brummer &Turner (1977), for periods of up to 800 hours at current levels of 4.0-8.0 mA, recorded slight local neural degeneration adjacent to the electrodes.