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Mohit N. Shivdasani, James B. Fallon, Chi D. Luu, Rosemary Cicione, Penny J. Allen, John W. Morley, Chris E. Williams; Cortical Responses to Single and Multiple-Electrode Stimulation of a Suprachoroidal Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2592.
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To determine whether stimulation of multiple electrodes using a single current source offers benefits over single electrode stimulation in a suprachoroidal retinal prosthesis.
A platinum electrode array (8x15mm, 7 rows x 12 columns of electrodes) was implanted into the suprachoroidal space in four normally-sighted, anesthetized, adult cats. We recorded multiunit activity across several sites from the visual cortex in response to monopolar stimulation of the retina with biphasic charge-balanced current pulses (return electrode in vitreous humor). Mean cortical thresholds and localization of activity were evaluated for three modes of retinal stimulation; single electrode, half-row (6 electrodes forming a horizontal line) and column (7 electrodes forming a vertical line). For each cortical site, the best single electrode, half-row and column of electrodes were defined as the electrode or line that evoked activity with the lowest threshold.
Stimulation of the best half-rows and columns were found to elicit activity with significantly lower (p<0.001) thresholds per electrode compared to best single electrode stimulation (Fig. 1A). Cortical localization, determined by the change in threshold as a function of distance in the retina from the best electrode or line was found to be significantly higher (p<0.001) for the half-rows compared to columns and single electrodes (Fig. 1B).
The lower thresholds and higher localization observed from multiple-electrode stimulation may likely be due to the line and orientation selectivity of cortical neurons. Such stimulation techniques could particularly aid in rapid presentation of lines and edges of objects with a suprachoroidal retinal prosthesis.
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