Aperiodic Stimulation Patterns for Visual Implants

Effective stimulation strategies are key to achieving successful neural implants for the treatment of neurological disorders, such as Parkinson’s disease, dystonia, chronic pain, and loss of vision and hearing. In recent decades, bionic vision systems have been developed for use as a substitute for natural vision in blind patients suffered from the loss of photoreceptors. Electrical pulses are applied to the retina or the cerebral cortex to restore partial vision to implant recipients. The current stimulation strategy used in visual implant is a regular, periodic pulse train, which is far from natural frequency dynamics. Studies have shown enhanced responses to temporal irregularity across tactile, auditory and visual modalities, in both animals and humans. Natural spiking patterns in the retina and cortex are highly irregular and characterized by their temporal variations. Introducing irregularities in the patterns that are used to activate retinal or cortical neurons may well enhance the efficacy of electrically-evoked cortical responses. However this approach has thus far been investigated only sparsely.We already investigated the effect of regular retinal stimulation on the spatial interactions of neurons in the visual cortex. This research received support allocated from the General Research fund for 2011/12 (CityU123412). Our results indicate that it will be essential to study the efficacy of irregular electrical stimulation in vivo, an approach which has not been pursued so far. Therefore we propose an investigation of the cortical activity at threshold currents, the spatially activated areas and the retino-cortical information transmission in live rats in response to irregular retinal stimulation.Retinal prosthesis currently uses regular, periodic pulse trains, which is far from any natural frequency dynamics. To date, no systematic study of primary visual cortical responses to irregular, aperiodic electrical stimuli in normal sighted rats or rats with retinal degeneration has been reported. This study will elucidate the efficacy of visual cortical responses to irregular temporal stimulus patterns in both normal sighted rats and rats with retinal degeneration. We will also examine the effects of spike train irregularity on excitatory and inhibitory neurons in both healthy and unhealthy rat visual cortices. Studying the interactions between irregular stimuli and excitatory as well as inhibitory networks in the visual cortex will help decipher the mechanisms underpinning brain plasticity in response to electrical stimulation. By addressing key challenges in human visual prosthetics, particularly desensitization to repetitive stimulation, this stimulation strategy could pave the way to high-resolution retinal prosthesis for long-term implantation.