Optimizing electrical stimulation parameters to enhance visual cortex activation in retina degeneration rats

In patients with degenerative retinal diseases such as retinitis pigmentosa and age-related macular degeneration, retinal prostheses offer a promising approach to restoring partial vision. Among these, epiretinal prostheses have shown encouraging preliminary clinical efficacy; however, optimizing stimulation parameters remains essential for improving efficiency and reducing power consumption. In this study, we investigated the effects of key electrical stimulation parameters- phase duration, frequency, and interphase interval (IPI) -on visual cortical electrically evoked potentials (EEPs) in both healthy Long-Evans (LE) rats and retinal degenerated (F1) rats. Our in vivo experiments on both LE and F1 rats revealed that shorter phase durations (500 µs) elicited activation in the primary visual cortex (V1) at lower charge thresholds. Our results also showed that responses to repetitive stimulation were significantly attenuated at high frequencies (10 and 20 Hz) compared to low frequency stimulation (1 Hz). Furthermore, we observed that longer phase durations (1000 and 1500 µs), as well as the inclusion of an IPI, resulted in a more confined spread of cortical activation. These findings suggest that adjusting phase duration can effectively reduce activation thresholds and spatially constrain cortical responses, and application of IPI can limit the extension of cortical responses, offering a potential strategy for enhancing the performance of epiretinal prostheses.