Retinal electrostimulation in rats: Activation thresholds from superior colliculus and visual cortex recordings

Retinal neuromodulation is an emerging therapeutic approach to restore functional vision to those suffering retinal photoreceptor degeneration. The retina encodes visual information and transmits it to the brain. Replicating this retinal code through electrical stimulation is essential to improving the performance of visual prostheses. In doing so, the first step relies on precise neural recordings from visual centers that allow studying the response of these neurons to electrical stimulation of the retina. This paper demonstrates the feasibility of a rat model to conduct highly reliable electrophysiological studies in the field of retinal neuromodulation. A disc electrode, implanted in the retrobulbar space was used to stimulate the retina of Long-Evans rats. Buzsaki multi-electro arrays were inserted in the superior colliculus (SC) to record electrical activity propagated from the retinal ganglion cells (RGCs). Activation thresholds calculated from local field potentials (visual cortex) and from neural spikes (SC) were contrasted. Both values were comparable to those in humans and in other animal models, and were slightly higher when estimated from SC recordings. However, differences were not statistically significant.