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Maesoon Im, Shelley I Fried; Indirect activation elicits strong correlations between light and electrical responses in ON but not OFF ganglion cells. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2378.
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© ARVO (1962-2015); The Authors (2016-present)
For improved quality of vision elicited by retinal prosthetics, it is important to understand the relationship between the parameters of stimulation and the resulting neural activity within the retina. Moreover, the prosthetic must be able to simultaneously create appropriate spiking patterns, e.g. those that match the light responses for each type of ganglion cell. Surprisingly, the similarities between light- and electrically-elicited response patterns have not been well studied. Here, we measured the response patterns elicited by epiretinal electric stimulation in RGCs and explored correlations between the electrically- and the light-elicited spikes within each type.
Cell-attached patch clamp was used to record spikes from RGCs in the isolated rabbit retina. RGCs were classified as ON or OFF cells by their response to stationary flashes. ON cells were further subdivided based on the presence of doublets or triplets in their spontaneous responses. After cell type classification, a monophasic half-sinusoidal wave (duration of 4ms, corresponds to half period of single 125Hz sine wave, amplitude range of -100µA to 100µA with 10µA increment) was presented typically 7 times to targeted RGCs. We recorded the spiking activity in 35 ON cells and 46 OFF cells.
The electric response patterns of RGCs had clear distinctions across cell types. ON BT cells (transient light responses with doublets in the spontaneous activity) always (n=18/18) contained three or more bursts of spikes while ON BS cells typically (n=13/17) responded with two bursts. ON cells generally showed strong correlations between electrically- and light-elicited responses in terms of strength and timing. In contrast, the electric response patterns from OFF cells did not neatly differentiate into two distinct groups. Also, the OFF cells had worse correlations to light responses than did ON cells. There were further differences between ON and OFF cells when the responses to repetitive stimulation were examined: each new stimulus strongly suppressed responses to previous stimuli in ON cells. This unique behavior of ON cells created differences between ON and OFF cells in response to repetitive stimulation with various inter-stimulus intervals.
Our results indicate that electric stimulation elicits responses that more closely match physiological responses in ON cells than in OFF cells.
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