Graeme Clark Collection
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ItemA multiple-electrode intracochlear implant for children( 1987)A multiple-electrode intracochlear implant that provides 21 stimulus channels has been designed for use in young children. It is smaller than the adult version and has magnets to facilitate the attachment of the headset. It has been implanted in two children aged 5 and 10 years. The two children both lost hearing in their third year, when they were still learning language. Following implantation, it was possible to determine threshold and comfortable listening levels for each electrode pair. This was facilitated in the younger child by prior training in scaling visual and electrotactile stimuli. Both children are regular users of the implant, and a training and assessment program has been commenced.
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ItemThe histopathological effects of chronic electrical stimulation of the cat cochlea(Cambridge University Press, 1983)The success of a cochlear implant depends on stimulating an adequate number of viable spiral ganglion cells. The effect of chronic electrical stimulation on ganglion cells is therefore an important consideration when assessing the effectiveness and safety of such a device. The histopathological assessment of chronic unstimulated intracochlear electrodes is now well documented (Simmons, 1967; Clark, 1973; Clark et al, 1975; Schindler and Merzenich, 1974; Schindler, 1976; Schindler et al, 1977; Sutton et al, 1980). These experimental studies have used a variety of electrode designs, materials and surgical techniques. However, all have shown that chronic implantation has little effect on the peripheral nerves and the spiral ganglion cells adjacent to an implant, provided the insertion procedure is free of trauma and infection.
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ItemDesign and fabrication of the banded electrode array( 1983)A multiple-channel electrode array must meet certain design requirements; these are listed in TABLE 1. First, there should be no trauma associated with the surgical insertion, and if there is a need to replace the array, this procedure should also be atraumatic. Second, it should be biologically inert. This means that it should be biocompatible with the tissues. When placed in the cochlea, the array should also not predispose the patient to local infection, and this is particularly important in children, in whom recurrent middle ear infections could spread to the inner ear. There should also be no risk of carcinogenicity with long-term implantation. Third, the electrode array should be designed so that the stimulus current can be localized to discrete groups of nerve fibers, and it should also be possible to stimulate as many groups as possible from the total remaining nerve population. Fourth, with long-term stimulation, there should be no significant corrosion of the electrodes used, and the electrical stimulation should not lead to damage of the tissues in the cochlea, especially the residual nerve fibers. Fifth, the electrode array should be mechanically robust and stable. It should not be prone to break as a result of repeated stress by the acceleration of the head during everyday movements. The array should also be capable of being fixed in place so that it will not shift its position. Sixth, it is desirable that the means of fabrication of the multiple-channel array should be simple and inexpensive. (From Introduction)
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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.