Electrical stimulation of the retina: aspects arising from retinal noise

Various impacts of the spontaneous neuronal noise on visual processing in the brain and the retina are extensively studying and discussing. Highly variable behavior is characteristic of healthy physiological systems, but dynamics of functional activity is simplifying in pathology and became either very ordered or characterized by entirely uncorrelated random oscillations. It has been demonstrated by several research groups that in hereditary retinal degeneration, sensory deafferentation arising from the loss of photoreceptors increases the spontaneous activity throughout the visual system and leads an aberrant rhythmic activity of retinal ganglion cells. In patients blind due to retinitis pigmentosa, retinal prosthetic devices are currently applying to obtain visual sensations induced by the electrical pulses. The right choice of the parameters of electrical stimuli is of great importance for achieving reliable responses from the RGCs and transmittance of encoded visual information to the brain. The temporal parameters of stimulation are supposed to be crucial to provide the further innovation development of such approach. We hypothesize that the periodic pathological activity in retinal degeneration not only is a factor that hampers the encoding of information and visual images of more quality. It also can aggravate the impact of deafferentation and play the negative role of in a formation of abnormal synaptic contacts during retinal remodeling contributing to the distortion of the complexity of neural circuits in the retina and the brain in retinal degenerations. We guess that the optical flicker and electrical stimulation therapy using the complex-structured (fractal) signals can be the promising approach providing both tuning the temporal sensitivity of the visual system and activation of the neuronal plasticity throughout the visual pathway. Future strategies of vision restoration apparently must be aimed to avoid the rhythmic activity in retinal circuits and to increase the quality of image representation. Here, we present the arguments that the utilizing the fractal modulation of the stimulating pulses in amplitude or frequency as well as using fractal temporal patterns in the background electrical prestimulation may be one of the prospective ways in future elaboration successful retinal prosthesis.