This project is designed to evaluate the feasibility of a visual prosthesis for totally blind individuals by stimulating chronically implanted microelectrodes in the visual cortex. A class 1000 clean room has been constructed in Building 49 for the complete fabrication of microelectrode arrays that will be implanted in primate visual cortex to evaluate reliability of the percutaneous connector system and the safety of the stimulation parameters. During FY1999, tissue blocks obtained from two non-human primates implanted with multi-electrode arrays (>30 electrodes each, one implanted for 10 weeks before sacrifice and the second for over four months) were reconstructed to permit histological examination of the electrode tracks and electrode tip regions in order to assess possible tissue reactions to the passage of different levels of stimulating current. The tip regions of many but not all electrodes were identified and are being processed for light and electron microscopic study. Initial evaluations indicate that tissue reaction is minimal, as has been found in previous primate implant testing. Given the successful tests of the electrode system, particularly the reliability of the pedestal connector, we anticipate that a group outside NIH may be interested in using the approaches and devices developed in LNLC for the first intracortical visual prosthesis designed for indefinite human implant. Therefore we are proceeding with fabrication of six electrode arrays designed for human implantation in the clean room in Bldg. 49. - primates, noble metal electrodes, miniature connector systems, pre-clinical testing
