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S.I. Fried, F.S. Werblin; Targeting Specific Ganglion Cell Types With Prosthetic Stimulation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3165.
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© ARVO (1962-2015); The Authors (2016-present)
To improve the quality of elicited percepts, retinal prosthetic devices must generate specific patterns of activity in retinal ganglion cells. To accomplish this, they must be able to identify and selectively activate independent ganglion cell types. Here, we have developed methods to classify targeted cells into known types and also to selectively activate a few specific ganglion cell types.
Cell–attached patch clamp recordings were used to measure spiking responses from individual retinal ganglion cells in the flat mount rabbit retina. Small tipped platinum–iridium epiretinal electrodes were used to deliver biphasic electrical stimulus pulses (0.1 ms) at 10 Hz. Thresholds for spike activation were measured as a function of the distance between the stimulating electrode and the soma (0–100 µm). Cells were classified into known types using light responses and dendritic morphology.
We found that thresholds varied as a function of ganglion cell type: alpha cells 19±3.6 µA, directionally selective (DS) cells 34±7.6 µA and local edge detectors (LED) 60±11 µA. These results are consistent with a model we developed that predicts spiking threshold is inversely proportional to dendritic field size (alpha>DS>LED). This result suggests that large ganglion cells can be selectively activated using low amplitude stimulus pulses. The model also suggests that smaller dendritic field cells can be selectively activated by applying specific patterns of stimulation from multiple electrodes. We also found that threshold increased as the stimulating electrode was moved away from the soma. The spatial profiles (plot of activation threshold vs. distance–from–soma) for the LED, DS and alpha ganglion cells were different, suggesting that these profiles can be used to identify cell type.
Our results suggest that a cell’s profile of threshold vs. distance–from–soma can be used as a ‘fingerprint’ to classify targeted ganglion cells into one of the known types. Once identified, ganglion cells with large dendritic fields can be selectively activated with low amplitude stimulation. The effectiveness of selectively activating small–dendritic–field ganglion cells with more complex stimulation schemes remains to be demonstrated.
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