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L. A. Hruby, P. Hottowy, W. Dabrowski, A. M. Litke, E. J. Chichilnisky; Patterned Electrical Stimulation of Distinct Retinal Ganglion Cell Types. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4229.
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© ARVO (1962-2015); The Authors (2016-present)
Epiretinal prostheses are designed to provide the retina with meaningful visual input by stimulating retinal ganglion cells (RGCs), inducing activity patterns that mimic normal responses to visual stimuli. Since these patterns occur among multiple RGC types, that transmit distinct visual information to the brain, it is crucial to understand the electrical response properties of each cell type. Furthermore, stimulation of bypassing axons may produce unintended patterns of activity in RGCs. We have probed these issues using a unique multi-electrode stimulation system applied to rat and primate retina.
A new multichannel electrical stimulation system was used in conjunction with micron-scale multielectrode arrays to electrically stimulate and record from rat and primate retina in vitro. The system injects current pulses through 61 independently-controlled electrodes, and includes circuitry to reduce the associated electrical artifact, allowing detection of RGC responses on the same electrode that is used for stimulation. Using this system, midget and parasol RGC responses to single and paired-electrode stimulation near the soma and along the axon were recorded.
The artifact-suppression circuitry allowed us to detect, for the first time, electrical stimulation of midget RGCs, which are the most numerous in the primate retina and are thought to be responsible for high-acuity vision. Midget and parasol RGCs exhibited similar stimulation thresholds. The thresholds for axonal and somatic stimulation partially overlapped. However, the probability of somatic stimulation exhibited a more gradual dependence on current amplitude than that of axonal stimulation. Bipolar stimulation oriented parallel to the axon tended to decrease threshold relative to single-electrode stimulation, while bipolar stimulation perpendicular to the axon tended to increase threshold.
Primate midget RGCs can be electrically stimulated at thresholds comparable to parasol RGCs. Differences in response characteristics to somatic and axonal stimulation, and shifts in axonal stimulation thresholds based on stimulus polarity and orientation, may be useful for avoiding the stimulation of bypassing axons.[LAH and PH contributed equally. AML and EJC contributed equally.]
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