Interaction of Prosthetic and Visible Stimuli Exhibits Similarities to Natural Cortical Processing

Prosthetic restoration of central vision in age-related macular degeneration (AMD) patients results in a complex visual scene in which the visual cortex is introduced with central prosthetic vision along with peripheral natural vision. The aim of the current research is to study the interaction between visible and prosthetic stimuli, which is of great clinical and scientific importance.

Implantation of photovoltaic subretinal implants in wild-type rats induced a localized photoreceptor degeneration above the implant, whereas the surrounding retina was left intact, similar to the localized retinal degeneration caused by AMD. Using a customized projection system, we stimulated prosthetic and natural vision with NIR and visible light (532nm), respectively, using a simple solid stimuli or complex patterns. We recorded visual evoked potentials (VEP) through screw electrodes implanted in the visual cortex.

Visible light background reduced the cortical responses to prosthetic flash stimuli, resembling the background effect on natural vision. Combined prosthetic and natural non-patterned stimuli (flashes and contrast steps) showed a simple cortical linear summation. In contrast, the responses to a central prosthetic alternating-grating target combined with natural visible flankers revealed lateral inhibition phenomenon, similarly to responses observed for similar natural visible stimuli. Interestingly, the lateral inhibition increased with target contrast for both prosthetic and natural light targets.

The observed striking similarities between cortical responses to patterned natural vision and to combined prosthetic-natural stimuli suggest that basic processing interactions are preserved when a combined information is presented to the visual cortex. These results are an important step for understanding the cortical processing of combined prosthetic and natural vision and can aid in prosthetic sight restoration in AMD patients