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S. Ryu, J. Ye, J. Lee, Y. Goo, K. Kim; Abnormal Rhythms in Electrically-Stimulated Activities of Rd1 Mice Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3054.
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© ARVO (1962-2015); The Authors (2016-present)
It is known that the neural activities of retinal ganglion cells (RGCs) are significantly changed after the degeneration of photoreceptor layer. Abnormal rhythmic activity in field potential was repetitively observed in these cases. This should induce alteration of electrically-stimulated RGC activities, and thus, prosthetic electrical stimulation pulse should be generated considering the altered response property. We investigated whether the temporal pattern of visual input can be encoded in population responses of RGC in photoreceptor-degenerated retina, by pulse amplitude modulation.
An in-vitro model of retinal implant was constructed using a 64 channel microelectrode array (MEA) and retina of rd1 mouse. Spontaneous and electrically-stimulated RGC activities were recorded. Electrical stimulation pulse trains were applied to one channel. The amplitudes of each pulse were modulated according to the temporal patterns of Gaussian waveforms and natural scenes. To quantify the accuracy of encoding the temporal information on input, spike train decoding was applied to decode the pulse amplitude time-series from the RGC activities.
Abnormal oscillatory rhythms (~10 Hz) were consistently observed from spontaneous field potentials. Rhythmic bursting of spontaneous spikes was also observed. The properties of evoked RGC spikes were markedly altered from normal retina. The oscillatory field potential showed phase-resetting behavior according to the pulse. The stimulated responses also showed rhythmic bursting pattern, presumably due to the abnormal rhythms in spontaneous activities. Multiple peaks were present in the poststimulus time histogram, with inter-peak intervals close to the inter-burst interval in rhythmic bursting of spikes. Despite this significant alteration, the response strength could be modulated by pulse amplitudes, and the temporal pattern of RGC firing closely resembled the pulse amplitude time-series. It was reconfirmed from the spike train decoding that the temporal information on visual input could be properly decoded from electrically-evoked RGC responses, as the case of normal retina.
Although the abnormal oscillation due to photoreceptor degeneration affects electrically-evoked RGC activities, the RGC spike trains of rd1 mice retinas could be still efficiently modulated by pulse amplitude. This suggests that successful encoding of temporal visual information by prosthetic electrical stimulation is feasible.
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