Spatiotemporal aspects of pulsed electrical stimuli on the responses of rabbit retinal ganglion cells

Implanted intraocular microelectrode arrays are being used to provide sight to individuals who are blind due to photoreceptor degeneration. It is envisioned that this retinal prosthesis will create the illusion of motion by stimulating focal areas of the retina in a sequential fashion through neighboring electrodes, much like the rapid succession of still images in movies and computer animation gives rise to apparent motion. Using a high-density microelectrode array, we examined the extracellularly recorded responses of rabbit retinal ganglion cells to a bar-shaped electrode array that was stepped at 50 μm increments at different rates across the retina and compared these respons2es to the responses generated to a similarly shaped light stimulus that was stepped across the retina. When the retina was stimulated at 1 step/s, retinal ganglion cells gave robust bursts of action potentials to both the electrode array and the light stimulus. The responses to the ‘moving’ electrode array decreased progressively with increasing stepping frequency. At 16 steps/s (highest frequency tested), the number of spikes per sweep and the number of bursts per sweep were reduced 75% and 67% respectively. In contrast, when the retina was stimulated at 16 steps/s with the ‘moving’ light stimulus, the number of spikes per sweep and the number of bursts per sweep were reduced only 43% and 25% respectively. These findings suggest that simple translation of object motion to sequential stimulation through neighboring electrodes may not be the best way to convey the perception of object motion in a patient with a retinal prosthesis.