Graeme Clark Collection

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    Direct current measurements in cochlear implants: an in vivo and in vitro study
    Huang, Christie Q. ; Carter, Paul M. ; Shepherd, Robert K. ; Seligman, Peter M. ; Tabor, Bruce ; Clark, Graeme M. ( 1998)
    Direct current (DC) was measured both in vivo and in vitro in cochlear implant electrodes with stimulation at moderate to high pulse rates in monopolar and bipolar modes. In vivo DC was approximately 2-3 times higher than that measured in vitro. In vivo DC levels were <100 nA even at very high rates, although DC levels increased as a function of stimulus rate and charge intensity. DC levels were lower: in the monopolar than in the bipolar stimulation condition. Stimulation with a monopolar capacitively coupled extracochlear electrode showed even lower DC levels in the intracochlear .electrodes. Our results indicated that the Nucleus electrode shorting system is able to maintain a low level of DC during very high rate stimulation for both monopolar and bipolar modes.
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    Peri-modiolar electrode arrays: a comparison of electrode position n the human temporal bone
    Shepherd, R. K. ; Treaba, C. G. ; Cohen, L. ; Pyman, B. ; Huigen, J. ; Xu, J. ; Clark, Graeme M. (Monduzzi Editore, 1997)
    This paper describes a radiologic evaluation of three types of peri-modiolar arrays, comparing their trajectory within the scala tympani with a standard Mini-22 electrode. All peri-modiolar arrays were found to lie closer to the modiolus for much of their insertion length compared with the standard array. While one design showed evidence for the potential of increased insertion trauma, two designs produced satisfactory results. Although further electrode development, temporal bone and histopathologic studies arE required, it would appear that the benefits of peri-modiolar electrode arrays will be realised clinically.
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    The interactions between the cytokine LIF and the neurotrophins on spiral ganglion cells
    Marzella, P. L. ; Clark, Graeme M. ; Shepherd, R. K. ; Bartlett, P. F. ; Kilpatrick, T. J. (Monduzzi Editore, 1997)
    The survival of auditory neurones depends on the continued supply of trophic factors. Early post-natal spiral ganglion cells (SGC) in a dissociated cell culture were used as a model of auditory innervation to test the trophic factors leukaemia inhibitory factor (LIF) and neurotrophin-3 (NT-3) for their ability, individually or in combination, to promote neuronal survival.
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    Electrical stimulation of the auditory nerve: the influence of electrode position on neural excitation
    Hatsushika, Shin-ichi ; Shepherd, Robert K. ; Clark, Graeme M. ; Funasaka, Sotaro (Kugler & Ghendini, 1990)
    Improved speech recognition among cochlear implant patients would appear to be dependent on a number of factors including improved speech processing strategies and an improvement in the effectiveness of electrically stimulating residual auditory nerve fibers (i.e. lower thresholds, wider dynamic ranges and more localized current spread). Previous human temporal bone studies have shown that free fit scala tympani electrode arrays generally lay along the outer wall of the scala tympani. Therefore, there is a relatively large distance between the electrode array and the residual neural elements within Rosenthal's canal. In the present study, we systematically varied the location of the electrode within the scala tympani to examine the influence of electrode position on neural excitation.