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Guenther Zeck, Florian Helmhold, Max Eickenscheidt; Receptive field properties in healthy and blind mouse retinas evaluated by stimulation using an implantable subretinal microchip. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5966.
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© ARVO (1962-2015); The Authors (2016-present)
Here, we examine to what extent receptive field properties known from light stimulation can be reproduced by electrical stimulation of healthy and photoreceptor-degenerated retinas using a a microchip which is part of subretinal implant. The microchip aims to replace missing photoreceptors by electrically stimulating surviving inner retinal neurons.
Whole-mount retinas from adult wild-type (C57Bl6) and adult rd10 mouse retinas were interfaced ganglion cell side up on the subretinal microchip. The chip contains an array of 1600 pixels (Inst. Microelectronics, University Ulm and Retina Implant AG), where each pixel converts incident light into biphasic voltage-controlled pulses. The pixel separation is 70 µm. Here, the stimulus amplitude was restricted to 1.8 Volts, with a short cathodic pulse preceding a 2 ms anodic stimulation phase. The response of retinal ganglion cells (RGCs) was recorded with a flexible, transparent and perforated microelectrode array (FLEX-MEA). The FLEX-MEA contained 16 extracellular electrodes (spatial separation: 150 µm) which allowed for continuous recording at high sampling rate (25 kHz). The spatial extent of the receptive fields was mapped using narrow stripe-like stimuli (70 x 300 µm2). For healthy retinas light-activated and electrically activated receptive fields could be directly compared by appropriate adjustment of the microchip’s light sensitivity.
At each stimulus position an the number of induced RGC spikes was evaluated. The spatial spike distribution for RGCs in healthy and blind retinas was well approximated by a Gaussian distribution. The light-driven receptive field size of RGCs in seeing retinas, as given by 2sigma, ranged between 200 - 350 µm. The same spatial range was found for electrically stimulated RGCs in healthy and photoreceptor-degenerated retinas. Simultaneously recorded RGCs discriminated between stimuli separated by 70 µm. Transient and sustained RGC stimulus responses were recorded upon electrical stimulation.
Electrically activated receptive fields in healthy and blind retinas share main features with light-activated receptive field. Spatial sensitivity may be further increased by reducing the electrode separation. Further tests are underway to compare the RGC’s temporal response characteristics for light and electrical stimulation.
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