Tissue response to a chronically implantable wireless, intracortical visual prosthesis (Gennaris array)

Objective. Cortical vision prostheses aim to restore visual percepts to those who have lost sight by delivering electrical stimulation to the visual cortex. These devices need to be implanted intracranially using subdural or intracortical microelectrodes, and should preferably dispense with the need of transcranial wiring. The risks of cortical tissue injury from mechanical trauma, material biocompatibility, heat generation, electrical stimulation and long-term immune responses need to be evaluated. In this paper, we investigate the biological response to a wireless cortical vision prosthesis (Gennaris array), by characterizing the histological changes that occur following chronic electrical stimulation. Approach. Ten arrays (7 active, 3 passive) were implanted in three sheep using a pneumatic insertor. Each device consisted of a wireless receiver and Application Specific Integrated Circuit encased in a ceramic box, and could deliver electrical stimulation through one of 43 electrodes. Main results. Stimulation was delivered through seven of these devices for up to 3 months and each device was treated as independent for further analysis. Cumulatively, over 2700 h of stimulation were achieved without any observable adverse health effects. Histology showed that the devices and implantation procedure were well tolerated by the brain with a similar tissue response to the more common Utah arrays. However, voltage transients across the stimulating electrodes were not measured so exact charge injection could not be verified. Significance. This work represents one of the first long-term tests of a fully implantable cortical vision prosthesis. The results indicate that long-term stimulation through wireless arrays can be achieved without induction of widespread tissue damage.