gms | German Medical Science

Our group has investigated the functional advantages and surgical and technical challenges of developing an intracortical visual prosthesis. We have conducted variety of human and primate studies which support the conclusion that implantation of an intracortical visual prosthesis in a human is functionally, technologically and surgically feasible. Through our primate studies we have developed insertion tools and procedures for implanting small independent stimulating modules over the occipital cortical surface which do not compromise the vascularity or functional integrity of cortex. Investigations of electrode tip size and composition have allowed us to protect both components of the electrode/tissue interface. Data from psychophysical testing of normally-sighted and low-vision subjects indicates that a prosthesis placed on the dorsolateral surface of the occipital lobe may permit adequately dense spatial resolution to elicit useful sensory input for individuals with blindness.

We have investigated the feasibility of cortically-induced artificial scoreboard vision by inducing punctate phosphenes through intracortical electrodes placed in the dorsolateral surface of the occipital lobe. Our psychophysical simulations have indicated that useful vision may be obtained from 300-600 stimulating electrodes that could be implanted within the superficial occipital cortex. Our system is based upon chips containing 16 wireless stimulation modules connected to penetrating iridium electrodes (Figure 1 [Fig. 1]). The electrodes are formed from etched iridium wire and have tips coated with activated iridium oxide film. The shafts of the electrodes are insulated with Parylene-C, and the tips are exposed by laser ablation, yielding a surface area of 2,000² microns. The physical placement of the electrodes is maintained by mounting them in a ceramic platform which forms the interconnect structure for the wireless custom integrated chip. The modules will receive their power and transmit data via a transcutaneous magnetic link.

Using our planned placement of the intracortical electrodes, combined with the projected phosphene maps and associated psychophysical studies, it appears feasible to produce usable visual function with about 40 modules implanted over the dorsolateral surface of the occipital lobe. One striking aspect of our psychophysical studies is how impoverished the simulated phosphene displays appeared when viewing them abstractly through the virtual reality goggles. Yet, the subjects were quickly, and rather easily, able to learn to use these scanned images as a means of performing eye-hand and mobility tasks. Since the subjects needed to rely upon memory while scanning the scene, one might ask if phosphenes produced by electrical stimulation might be stored in short-term memory as easily as the simulated phosphenes were. In order to effectively use scanning as a method of integrating the “scoreboard-like” patterns, the subjects needed to build up the perceptual information in constructing the mental image. It remains unclear to what extent this same integration might be accomplished using artificially–induced phosphenes via electrical stimulation. We have not yet demonstrated the emergence of higher-order percepts or objects (e.g., perceiving a line from a row of punctate phosphenes) in our primate or human studies. We consider this an important milestone for all approaches to a visual prosthesis. Despite these limitations, our assessment is that it is technologically and surgically feasible to implant intracortical electrodes within the human cortical visual system, and the psychophysical studies support the likelihood of prosthesis efficacy.

This lecture is available as video recording (Attachment 1 [Attach. 1]).