Thalamic Visual Prostheses: Consistent phosphenes generated by subcortical electrical stimulation

Abstract

PURPOSE: in this study, a direct electrophysiological proof for the feasibility of visual prostheses implanted in the thalamus is presented, in dorder that could outperform the cortical ones. METHODS: Most of the up to day work in visual prostheses has been 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 anesterized rats. A serie of visual stimuli (Si) was presented to one eye. The contralateral thalamic (Rthi) response and the cortical neurons (Roxi) 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 response (Roxi*) to this electrical stimulation of the thalamus were recorded. The parameters of the electrical patterns were adjusted to abtain the best matching between (Roxi) and (Roxi*) that means between the response to natural stimulation of the eye and the response to the electrical sitmuli to the thalamus. RESULTS: results about layout and characteristics of lateral geniculate nucleus neurons of the thalamus of rats "in vivo" have shown the vest locations to cronically implant electrodes. These electrodes locations will be used to introduce viusla 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 prostheses in 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 techinical and physiological limitations. All these limitations are solved for this method proposed in this study.