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Mohit N. Shivdasani, Rosemary Cicione, James B. Fallon, Graeme D. Rathbone, Chris E. Williams; Spatiotemporal Interactions Using Paired Electrical Stimulation of the Retina with a Clinical Grade Implant. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5543.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal prostheses aim to provide functional vision using spatiotemporal patterns of electrical stimulation on potentially thousands of electrodes. In this study we used a paired pulse paradigm to characterise the effect of time, distance and current between pairs of electrical stimuli in the retina on multi-unit spiking activity in the primary visual cortex.
A clinical grade retinal electrode array made from silicone and platinum was implanted in the suprachoroidal space of three normally-sighted anesthetized adult cats. The retina was stimulated using a paired-pulse paradigm with biphasic current pulses where the current of the first pulse and the delay between the two pulses were varied (0-1.5mA; 1.025-500ms), while the current of the second pulse was kept constant at a near threshold level. Pulses were presented either on the same electrode (0mm separation) or on pairs of electrodes separated by 1 or 2mm. Multi-unit spiking activity was recorded from the primary visual cortex using a 60-channel array (Blackrock Microsystems, UT). Interactions were quantified on each cortical recording site by comparing spike counts following the second pulse in the paired-pulse paradigm with that evoked by presentation of the second pulse alone.
Analysis from four (0mm separation), three (1mm separation) and two (2mm separation) retinal electrode pairs and up to 87 cortical recording sites showed that interactions were dependent on the current of the first pulse, delay between the pulses and the distance between electrodes forming the pairs. For delays between 20-80ms, the presence of the first pulse significantly decreased spiking activity following the second pulse (ANOVA, p<0.001) compared to activity with the second pulse alone. Interestingly, although less evident for larger electrode separations, this effect was observed even when the first pulse was presented at sub-threshold levels. At delays beyond 100ms, there were no signification interactions between the stimuli.
Spatiotemporal interactions with a clinical grade retinal prosthesis occur for to up to 100ms and extend over several millimeters of the retina. Results of such interactions should be carefully taken into account when developing complex spatiotemporal patterns of electrical stimulation for retinal prostheses.
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