This project is designed to evaluate the feasibility of a visual prothesis for totally blind individuals by stimulating chronically implanted microelectrodes in the visual cortex. As reported last year, a 42-year- old woman who has been blind for 22 years was implanted with an array of 38 electrodes in the visual cortex. Stimulation of individual electrodes produced sensations of light called phosphenes. Phosphenes were produced with 34 of the 38 electrodes with currents that were 100 to 1000 times lower than had been reported for surface stimulation of the visual cortex. From the data obtained from the first patient, the design concepts for the next patient-implant have been developed. Four arrays of 32 dual hat pin electrodes will be chronically implanted in the visual cortex for a total of 256 electrodes. A new computer control system with TV camera input and a 256-channel microprocessor-controlled stimulator are under development. A miniature percutaneous connector system has been developed that will contain 64 lead wires. Four of these connectors will be implanted in the next human subject to activate the 256 electrodes. A number of new electrode fabrication techniques have been developed and the resultant electrode arrays and percutaneous connector will be tested in animals prior to the next human implant.
