How the retinal network reacts to epiretinal stimulation to form the prosthetic visual input to the cortex

Abstract

We considered the problem of determining how the retinal network may interact with electrical epiretinal stimulation in shaping the spike trains of ON and OFF ganglion cells, and thus the synaptic input to first-stage cortical neurons. To do so, we developed a biophysical model of the retinal network with nine stacked neuronal mosaics. Here, we describe the model's behavior under (i) electrical stimulation of a retina with complete cone photoreceptor loss, but an otherwise intact circuitry and (ii) electrical stimulation of a fully-functional retina. Our results show that electrical stimulation alone results in indiscriminate excitation of ON and OFF ganglion cells and a patchy input to the cortex with islands of excitation among regions of no net excitation. Activation of the retinal network biases the excitation of ON relative to OFF ganglion cells, and in addition, gradually interpolates and focuses the initial, patchy synaptic input to the cortex. As stimulation level increases, the cortical input spreads beyond the area occupied by the electrode contact. Further, at very strong stimulation levels, ganglion cell responses begin to saturate, resulting in a significant distortion in the spatial profile of the cortical input. These findings occur in both the normal and the degenerated retina simulations, but the normal retina exhibits a tighter spatiotemporal response. The complex spatiotemporal dynamics of the prosthetic input to the cortex that are revealed by our model should be addressed by prosthetic image encoders and by studies that simulate prosthetic vision.

A cortical (V1) neurophysiological recording model for assessing the efficacy of retinal visual prostheses

“…5B), during the second response phase, both spiking and LFP activity are much stronger than during the first response phase. This is consistent with findings from our simulations (Cottaris and Elfar, 2005), which show that indirect stimulation of bipolar cells produces more robust responses than direct stimulation of ganglion cells. Similar observations are seen in the activity sampled by electrodes 11, 17, 51, 56 (outlined in red in Fig.…”

Spatio-Temporal Electrode Mapping and Local Interleaved Stimulation Method (STEMLIS) for Artificial Sight Systems

“…The electrical stimulation of the retina layer with microelectrodes causes perceptions of phosphenes, and it is known that the intensity of electric fields decreases as a function of distance from the electrode [36,37].…”

The Effect of the Electrical Stimulation on Temperature Rise in the Retinal Tissue for Visual Prostheses

“…Thermal insulation is a boundary condition and means that the domain is insulated, that is, heat cannot pass from one side to another, (2).…”

“…Degenerative retinal diseases that result in the most prevalent blindness are Retinitis Pigmentosa (RP) and Age Related Macular Degeneration (AMD) [2]. Degenerative retinal diseases that lead to the most prevalent blindness are AMD and RP throughout the world and unfortunately there is no effective treatment method ranging from rebirth of photoreceptors from stem cells to neuro-protective therapy [3], [4].…”