Network-mediated responses of ON ganglion cells to electric stimulation become less consistent across trials during retinal degeneration

Stimulation Strategies for Improving the Resolution of Retinal Prostheses

Electrical stimulation using implantable devices with arrays of stimulating electrodes is an emerging therapy for neurological diseases. The performance of these devices depends greatly on their ability to activate populations of neurons with high spatiotemporal resolution. To study electrical stimulation of populations of neurons, retina serves as a useful model because the neural network is arranged in a planar array that is easy to access. Moreover, retinal prostheses are under development to restore vision by replacing the function of damaged light sensitive photoreceptors, which makes retinal research directly relevant for curing blindness. Here we provide a progress review on stimulation strategies developed in recent years to improve the resolution of electrical stimulation in retinal prostheses. We focus on studies performed with explanted retinas, in which electrophysiological techniques are the most advanced. We summarize achievements in improving the spatial and temporal resolution of electrical stimulation of the retina and methods to selectively stimulate neurons with different visual functions. Future directions for retinal prostheses development are also discussed, which could provide insights for other types of neuromodulatory devices in which high-resolution electrical stimulation is required.

Optimal Electric Stimulus Amplitude Improves the Selectivity Between Responses of ON Versus OFF Types of Retinal Ganglion Cells

Outer retinal degenerative diseases destroy photoreceptors primarily in the retina, resulting in a profound vision loss. Fortunately, surviving retinal neurons can be electrically stimulated using retinal prostheses to re-transmit visual information. Although retinal prostheses are promising for sight restoration, the best performance is still sub-optimal. For the enhanced performance, it is critical to optimize stimulation parameters. This study explored how stimulus charge and current amplitude alters responses of retinal ganglion cells (RGCs). From the isolated mouse retina, spiking activities of alpha ON, OFF sustained, and OFF transient RGCs were recorded in response to epiretinally-delivered cathodal current pulses ranging from -10 to [Formula: see text]. We have found that intermediate current amplitudes (-30 and [Formula: see text]) maximize the response ratio of ON over OFF types. Also, the ON/OFF response ratio was always bigger for 10-ms-long than 5-ms-long stimuli. It was because, by the longer pulses, ON RGC responses were always significantly enhanced ( ) while OFF RGC responses were minimally changed ( ). Given the earlier work reporting electrically-elicited responses are more natural in ON than OFF RGCs, the present study suggests effect strategies of more selective activation of ON RGCs for improved efficacy of retinal implant.