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P. R. Troyk, D. Bradley, M. Bak, S. Cogan, C. Kufta, D. McCreery, E. Schmidt, V. Towle; An Intracortical V1 Visual Prosthesis: Balancing Functional, Surgical, and Technological Considerations. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2571.
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© ARVO (1962-2015); The Authors (2016-present)
Our project to implement a cortical visual prosthesis has reached the stage at which we are planning for implantation of a prototype system in a human. We have used a team-based method to determine how the first human implantation experiment would be configured and implemented. We are contrasting functional, surgical, and technological issues so as to arrive at an achievable experimental protocol.
A literature survey was performed to determine the locations within area V1 for implantations of up to 1000 intracortical metal microelectrodes. From a surgical perspective we considered the safety of the human subject balanced against a prediction of prosthesis sensory functionality. We assessed which regions of the V1 retinotopic map could be suitable for implantation of stimulation modules, each containing 16 electrodes. For ~1000 electrodes, up to sixty 3mm-diameter modules would have to be implanted, and we performed a surgical analysis of to what extent the surface of the pole, midline, and Calcarine fissure would be available for electrode placement.
Our study revealed that it may be desirable to approach the surgery in two phases. In phase one, a small number of 16-electrode modules would be implanted for a period of 2-4 months to demonstrate the stability of the electrode neural interface. In phase two, assuming stability of the interface, up to sixty modules would be placed on the V1 pole in the same volunteer. Even with 1000 electrodes, it is uncertain whether or not there would be a sufficient density of phosphenes to rely upon a bit-map approach to vision. Although the spatial coverage of the visual field from the posterior pole of V1 would be limited, our preliminary information theory analyses suggest that spatial scanning will significantly compensate for the lack of spatial coverage. However present data do not allow an assessment of well artifically-produced phosphenes are are stored in short-term memory.
An intracortical visual prosthesis seems feasible from the viewpoint of functionality, surgical feasibility, and technological availability. Presently we are designing the human psychophysical experiments that would be performed using the implanted system.
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