Purpose: To restore visual function via the prosthetic stimulation of retina, visual information must be properly represented in the electrically evoked neural activity of retinal ganglion cells (RGCs). In this study, the RGC responses in photoreceptor-degenerated retinas were shown to actually encode temporal information on visual input when they were stimulated by biphasic pulse trains with amplitude modulation.
Methods: Multiple RGC spike trains were recorded from rd1 mouse retinal patches mounted on planar microelectrode arrays while being stimulated by pulse trains with amplitudes modulated by the intensity variation of a natural scene. To reconstruct the time series of pulse train amplitudes from the evoked RGC activity, spike train decoding was performed. The accuracy of decoding-that is, the similarity between the original and decoded pulse amplitudes-was observed, to evaluate the appropriateness of the stimulation.
Results: The response strengths of the RGCs could be successfully modulated when the pulse amplitude was varied between 2 and 20 μA. When the amplitude modulation range and pulse rates were determined elaborately, the temporal profile of the intensity could be successfully decoded from RGC spike trains, although abnormal oscillatory background rhythms (~10 Hz) were consistently present in the rd1 spike activity.
Conclusions: The results extend previous findings on the possibility of visual information encoding by electrical stimulation of normal retinas to stimulate degenerated retinas, in which neural activity is significantly altered. This supports the feasibility of encoding of temporal information by retinal prostheses.