Thalamic Visual Prostheses: Consistent Phosphenes Generated by Subcortical Electrical Stimulation

Purpose: : In this study, a direct electrophysiological proof for the feasibility of visual prostheses implanted in the thalamus is presented, in order that could outperform the cortical ones. Methods: : Most of the up to day work in visual prostheses has been centered in the development of retinal and cortical devices and their implant to blind patients. On the contrary, current research is centered on visual neuroprostheses for subcortical structures and in particular for the thalamus. In this study, multielectrodes have been implanted in the visual thalamus and the cortex of anestetized rats. A serie of visual stimuli {Si} was presented to one eye. The contralateral thalamic {Rthi} response and the cortical neurons {Rcxi} responses were recorded. After that, electrical patterns {Rthi*} that mimick the thalamic responses (which were recorded during the natural stimulation of the eye) were generated. Next, the electrical patterns {Rthi*} to the thalamus were injected. At the same time, cortical responses {Rcxi*} to this electrical stimulation of the thalamus were recorded. The parameters of the electrical patterns were adjusted to obtain the best matching between {Rcxi} and {Rcxi*}, that means between the response to natural stimulation of the eye and the response to the electrical stimuli to the thalamus. Results: : Results about layout and characteristics of lateral geniculate nucleus neurons of the thalamus of rats "in vivo" have shown the best locations to cronically implant electrodes. These electrodes locations will be used to introduce visual signals to the visual cortex. The results obtained shows the electrodes’ right location in the lateral geniculate nucleus. Also to establish the stimulation’s electrical characteristics which is necessary to provide to the electrodes and the space-temporal parameters which is necessary to create. Conclusions: : The applicability of retinal prostheses is restricted, unfortunatelly, either to the unavailability of retinal and/or optic nerve structures, or because of problems related to the retinal implants themselves. On the other hand cortical prostheses present several technical and physiological limitations. All these limitations are solved for this method proposed in this study.