Graeme Clark Collection
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ItemIntracochlear electrical simulation of normal and deaf cats investigated using brainstem response audiometry( 1983)Brainstem response audiometry for intracochlear electrical stimulation of normal-hearing and deafened cats was investigated. In normal cochleas the brainstem response amplitude grew slowly near threshold as a current-amplitude dependent process, identified as electrophonic in origin. This terminated in a rapidly growing charge-dependent process at approximately 20 dB above threshold, identified as direct electrical stimulation of the auditory nerve. Small levels of white noise (25-35 dB SPL) were sufficient to mask most of the electrophonic response, leaving the direct stimulation process essentially unmodified. In cochleas damaged with d.c. currents and loud sounds, only a rapidly growing charge-dependent process was observed which grew similarly to that in normal-hearing cats but occurred at lower currents. This indicates that possibly the electrical properties of the cochlea were altered in the deafening process, suggesting the inadequacy of normal animals as deaf models for electrical stimulation. Using the technique of derived brainstem responses, it was shown that direct electrical stimulus components were localized to the vicinity of the stimulus electrode with electrophonic components distributed more widely. However, at high currents there was some evidence of the stimulus spreading into the internal auditory meatus.
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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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ItemAn improved model of electrical stimulation of the auditory nerve(Monduzzi Editore, 1997)Mathematical models are a useful means of formally describing and investigating pertinent features of complex systems such as the human auditory system. These features may be deduced from physiological and psychophysical experiments utilising animal models or humans, and from engineering studies. Historically, models of the auditory nerve's (AN) response to electrical stimulation have ignored randomness in single-fiber activity which has been recorded in physiological studies. These models, however, have been unable to accurately predict a number of important psychophysical phenomena. In this study, a model that incorporates random activity of the AN is presented, and is shown to predict psychophysical performance. These results indicate that random activity is indeed an important part of the response of the AN to electrical stimulation.
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ItemResponses from single units in the dorsal cochlear nucleus to electrical stimulation of the cochlea( 1992)To help improve our understanding of how the brain responds to electrical stimulation of the auditory nerve we have examined the responses of dorsal cochlear nucleus (DCN) units to both acoustic stimulation and electrical stimulation of the cochlea. This work extended our previous studies which have compared the responses to electrical and acoustic stimulation In the auditory nerve (Javel et al 1987, Ann. Otol. Rhinol. laryngeal. Suppl. 128, 96:2630) and the ventral cochlear nucleus (Shepherd et al 1988, NIH Contract NO1-NS-72342, 5th Quarterly Progress Report).