Analysis of retinal and cortical response to electrical stimulation by Subretinal implant in rodent model

Abstract

Purpose: This research aims to develop and improve the use of retinal prosthesis in animal model. For that purpose, we measured retinal and cortical response to direct subretinal electrical stimulation to understand how the patterns of stimuli can be adapted to improve stimulation to get closer to the response evoked by natural visual stimuli.

Methods: In a rat model, a comparative analysis of the functional impact of similar stimulation of a subretinal implant is done at two levels, (i) in the retina in vitro by multi electrodes array and (ii) in vivo in the primary visual cortex by optical imaging recordings. Optical imaging permits a functional mapping of the cortex, using light reflection and absorption changes depending on the rate of blood oxygenation. Diverse parameters were investigated: stimulus shape and polarity, intensity, size and location.

Results: At the cortical level, we have quantified the size, position and intensity of the point-spread function in response to the various electrical stimulations and compared them to those generated by calibrated light stimuli. The point-spread function was much larger for electrical stimulations compared to visual stimulation. We are currently performing retinal recordings of ganglion cells, while the prosthesis is on the photoreceptor side. We will compare the size of ganglion cell receptive fields to the size of the electric field activation to see if a difference in the size of the region activated by the two stimulations in the retina could explain the difference observed at the cortical level. The ability to evaluate in vitro within the retina and in vivo the cortical responses induced by the prosthesis allowed us refining the patterns of electrical stimulation to get closer to a natural visual activation.

Conclusions: These results offer interesting prospect for improving the design of prostheses as well as their patterns of stimulation for a medical application

Keywords: 688 retina • 755 visual cortex • 494 degenerations/dystrophies