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B. B. Thomas, L. L. Chan, A. Ray, M. S. Humayun, J. D. Weiland; Spatial Properties of Multi-Electrode Epiretinal Stimulation Evaluated from the Rat Superior Colliculus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3021.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the spatial properties of multi-electrode, epiretinal electrical stimulation, by mapping electrical evoked responses from the surface of rat superior colliculus (SC).
For epiretinal electrical stimulation, a stainless steel, dual barrel electrode 75 µm tip diameter (each) and 115 µm edge-to-edge spacing was advanced through the vitreous of the eye of normal Copenhagen and S3343ter-line-3 retinal degenerate (RD) rats through an incision made in the sclera. The electrode tip was positioned proximal to the epiretinal surface as evidenced by corresponding changes in the electrode impedance. For electrophysiological mapping, multiunit signals were recorded from the surface of the SC at 150-250 µm apart while individual electrodes were stimulated using a constant biphasic current source (1 ms pulse duration, amplitude range of 1 - 100 µA).
Epiretinal electrical stimulation using dual barrel electrodes evoked responses in the SC of both normal and RD rats. The responses were recorded from the surface of the SC corresponding to the placement of the stimulation electrodes inside the eye. Distinct stimulation areas representing individual electrodes could be mapped from the SC surface. Differences were observed between the two electrodes in the stimulus threshold level (range, 2 uA - 10 uA, 1 ms pulse width) and the distribution pattern of the SC responses. At the threshold stimulus level, SC responses evoked by individual electrodes ranged from 14% - 48% of the total recording sites. Almost 90% of the above sites were independent (represented by one of the electrodes) while the remaining sites (range, 6%-12%) were overlapping (represented by both electrodes).
In rats, epiretinal electrical stimulation using dual barrel steel electrode produced spatially distinct responses in the SC that are consistent with the known retinotopic projection. Differences between the two electrodes based on stimulus threshold and distribution pattern of the SC evoked responses may be attributable to the possible differences in the retina-electrode proximity.
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