Graeme Clark Collection

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Author: Clark, Graeme × End date: 1999 × Start date: 1990 × Type: Conference Paper × Subject: electrical stimulation × Subject: otolaryngology ×

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Now showing 1 - 5 of 5
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    The effect of pulsatile intracochlear electrical stimulation on intracellularly recorded cochlear nucleus neurons
    Paolini, Antonio, G. ; Clark, Graeme M. (Monduzzi Editore, 1997)
    The anterior division of the ventral cochlear nucleus (AVCN) is the first relay station of the auditory pathway. We examined responses of neurons in the A VCN to intracochlear electrical stimulation using in vivo intracellular recordings. Twin pulse stimulation results indicated that these neurones evoke action potentials which are able to follow pulsatile stimulation at high rates. This ability to respond to each pulse along the stimulus train diminished when stimulus duration was increased to 50 ms. At rates 400 Hz and below in all neurones tested a deterministic response was seen to this longer duration pulsatile stimulation. With increasing rate of stimulation the response become more stochastic with apparent loss of encoding ability. These results have in1pIications in the clinical application of cochlear implants operating at high stimulus rates.
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    Temporal coding in auditory neurons to electrical stimulation
    Hocking, J. ; Brown, M. ; Clark, Graeme M. (Monduzzi Editore, 1997)
    Different electrically evoked response properties are elicited by similar acoustically differentiated AVCN units. Discharge entrainment and synchrony of some AVCN units is maintained throughout the electrical stimulus duration at all rates, similar to that described for auditory nerve fibres. Other units exhibit a decline in discharge entrainment over the duration of the electrical stimulus with increasing rate. Within this group of units, some exhibit a highly synchronous response while others show a decline in the response synchrony with increasing stimulus rate.
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    Cochlear implant research directions
    Clark, Graeme M. (Monduzzi Editore, 1997)
    Frequency Coding: Initial cochlear implant research (Clark, 1969) showed that with electrical stimulation of the auditory nerve there is an electroneural "bottle-neck" limiting the flow of information from sound to the central auditory nervous system. This electroneural "bottle-neck" is due to the difficulty in simulating with electrical stimulation the temporal as well as the place coding of frequency. One of the main aims of our research is to improve cochlear implant performance by widening the "bottle-neck" with better simulation of the temporal and place coding of frequency. Temporal coding is considered to be due to a direct relationship between the intervals between action potentials and the period of the sound wave. Temporal coding is thought to apply to low frequencies, but its importance for high frequencies is still not clear. Place coding is due to excitation of specific sites within the cochlea and the central auditory pathways 'so that a frequency scale is preserved anatomically (i.e. the brain is organized tonotopically).
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    An improved model of electrical stimulation of the auditory nerve
    Bruce, I. ; Irlicht, L. S. ; White, M. ; O'Leary, S. J. ; Dynes, S. ; Javel, E. ; Clark, Graeme M. (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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    A digital computer model of electrical stimulation in the human cochlea for auditory prosthesis research
    Tong, Yit C. ; Sapozhnikov, A. ; Wills, R. ; Chang, J. S. ; Clark, Graeme M. ( 1990)
    A three-dimensional model of electrical stimulation in the human cochlea has been developed and implemented on a digital computer. The model was used to estimate the distributions of electric potential and current density in the human cochlea in response to electrical stimulation using scala tympani electrodes. The computed distributions were used to investigate the relative merits of two scala tympani electrode designs. The results showed that the electrode design consisting of a medial electrode pair in the scala tympani is a more viable alternative than a lateral electrode pair for patients suffering from profound-to-total hearing impairment.