Graeme Clark Collection
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ItemPhysiological and histopathological effects of chronic intracochlear electrical stimulation(Monash University Press, 1983)Direct and r.f. currents are known to result in destruction of neural tissue. However, it is now apparent that non-destructive electrical stimulation can be achieved by the use of biphasic pulsatile stimuli (Lilly, 1960; Mortimer et al., 1970; Hughes et al., 1980). Although maximum biologically safe stimulation regimes have yet to be clearly defined, the evidence of a number of investigators suggests that charge density per phase and charge injection per phase are important parameters when establishing biologically safe levels of electrical stimulation (Pudenz et al., 1975; Pudenz et al., 1977; Brown et al., 1977; Babb et al., 1977). Furthermore, considerable attention has been given to ensure that the stimulus is not producing adverse electrochemical reactions that could result in physical or toxic injury to the biological environment. Brummer et al. (1977) have defined the upper limit of electrochemically safe electrical stimulation for platinum electrodes as charge balanced biphasic pulses at a maximum charge density of 300 ?C/cm2 geom./phase.
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ItemThe auditory brainstem response in hearing and deaf cats evoked by intracochlear electrical stimulation(Monash University Press, 1983)This study was performed to investigate in detail the auditory brainstem response (ABR) for intracochlear electrical stimulation. Brainstem response audiometry is a simple, noninvasive procedure with the responses under many stimulus conditions being readily understood in terms of single auditory nerve discharge properties. The amplitude and latency behaviour of the Nl brainstem response correlates well with that recorded directly from the auditory nerve (Huang & Buchwald, 1978). In addition, the brainstem response can be divided into frequency-specific components corresponding to tonotopical locations in the cochlea, as exhibited in the method of derived responses (e.g. Parker &Thornton, 1978). It is therefore well suited to both physiological and clinical investigation of auditory function and therefore should be useful in evaluating auditory function under conditions of electrical stimulation of the cochlea.
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ItemElectrical stimulation of the human cochlea: psychophysical and speech studies(Plenum Publishing Corporation, 1981)This report describes psychophysical and speech studies conducted on two of our post-lingually deaf patients implanted with the nature of the hearing sensations produced by the individual electrodes, and to investigate the feasibility of the transmission of speech information to higher centres by means of cadences of stimulation using on electrode at a time. Two totally deaf patients (MC1 and MC2) participated in these studies.
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ItemThe influence of electrode geometry on the electrically evoked auditory brain stem response( 1988)The electrically-evoked auditory brainstem response (EABR) consists of a series of far-field potentials that reflect synchronous neural activity within the auditory brainstem in response to a transient electrical stimulus. The EABR appears relatively simply organized in terms of its amplitude and latency behaviour. The growth in amplitude of wave IV of the EABR, for example, reflects changes in the amplitude of the electrically-evoked VIII nerve compound action potential as a function of stimulus intensity. In addition, single unit population studies have shown a monotonic relationship between the growth in EABR amplitude and the number of nerve fibres being stimulated (Merzenich and White, 1977). The EABR can therefore, provide an insight into the response of the auditory nerve to electrical stimulation. We have used this technique to investigate the efficacy of electrical stimulation of the auditory nerve using a variety of stimulating electrode geometries.