Spatiotemporally Patterned Electrical Stimulation of Retina

Abstract

Purpose: : The aim of an epiretinal prosthesis is to provide useful visual information to the brain by inducing activity in retinal ganglion cells (RGCs). Because normal vision entails complex spatiotemporal patterns of RGC activity, this goal will require the use of spatiotemporal patterns of electrical stimulation. In addition, the use of spatial patterns has the potential to help specifically activate a target RGC while avoiding activation of neighboring RGCs and passing axons.

Methods: : RGCs from rat and primate retinas were recorded and stimulated in vitro using a custom multichannel system connected to an array of 61 platinized electrodes with diameters of 5-10 microns and inter-electrode spacing of 30 or 60 microns. Current pulses were applied, while simultaneously monitoring the responses of all recordable RGCs in the region.

Results: : Responses of individual RGCs stimulated with pairs and triplets of electrodes located near their somas were recorded. These responses were compared to responses to stimulation with a single electrode. Addition of a second stimulating electrode sometimes increased and sometimes decreased the threshold to activation by the primary electrode, depending on the locations of the primary and secondary electrodes. Patterned stimulation with triplets of electrodes could be predicted based on responses to pairs of electrodes using a simple linear model. The possibility of interactions between multiple cells activated in spatiotemporal patterns was tested by stimulating 3-4 cells simultaneously and in sequences with temporal offsets as small as 1 ms. Under these conditions, RGC responses closely resembled responses to stimulation in isolation.

Conclusions: : The effects of spatially patterned electrical stimulation of RGCs is predictable using simple models. Such models may be useful for determining optimal stimulation patterns to maximize the probability of stimulating a target cell while avoiding stimulation of neighboring cells and passing axons. Spatiotemporal patterns of electrical stimulation are capable of generating spatiotemporal patterns of RGC activity with minimal unwanted interactions. [LHJ and PH contributed equally; EJC and AML contributed equally]

Keywords: retina • electrophysiology: non-clinical • ganglion cells