Multiple factors may influence the performance of a visual prosthesis based on intracortical microstimulation: nonhuman primate behavioural experimentation

Abstract

We hypothesize that a visual prosthesis capable of evoking high-resolution visual perceptions can be produced using high-electrode-count arrays of penetrating microelectrodes implanted into the primary visual cortex of a blind human subject. To explore this hypothesis, and as a prelude to human psychophysical experiments, we have conducted a set of experiments in primary visual cortex (V1) of non-human primates using chronically implanted Utah Electrode Arrays (UEAs). The electrical and recording properties of implanted electrodes, the high-resolution visuotopic organization of V1, and the stimulation levels required to evoke behavioural responses were measured. The impedances of stimulated electrodes were found to drop significantly immediately following stimulation sessions, but these post-stimulation impedances returned to pre-stimulation values by the next experimental session. Two months of periodic microstimulation with currents of up to 96 μA did not impair the mapping of receptive fields from local field potentials or multi-unit activity, or impact behavioural visual thresholds of light stimuli that excited regions of V1 that were implanted with UEAs. These results demonstrate that microstimulation at the levels used did not cause functional impairment of the electrode array or the neural tissue. However, microstimulation with current levels ranging from 18 to 76 μA (46±19 μA, mean±std) was able to elicit behavioural responses on 8 out of 82 systematically stimulated electrodes. We suggest that the ability of microstimulation to evoke phosphenes and elicit a subsequent behavioural response may depend on several factors: the location of the electrode tips within the cortical layers of V1, distance of the electrode tips to neuronal somata, and the inability of nonhuman primates to recognize and respond to a generalized set of evoked percepts.

Properties of electrically evoked potentials activated by optic nerve stimulation with penetrating electrodes of different modes in rabbits

“…Visual prostheses have proved to be a promising way to restore partial functional vision for patients with RP. Three major types of visual prostheses have been investigated according to the stimulation locations: cortical prostheses [3][4][5][6][7], retinal prostheses using epi-and subretinal stimulation , and optic nerve (ON) prostheses [31][32][33][34][35][36][37][38][39][40][41]. The retinal prosthesis is the most developed type among the three, and the Argus II epiretinal prosthesis has been approved by the European CE and the US FDA for clinical use [23].…”

Electronic Approaches to Restitute Vision in Patients with Neurodegenerative Diseases of the Retina

“…A major limitation of this work is the development of an image-processing system to convert an electronic image captured by a camera into a real-time data stream for stimulation of the implanted electrodes in a way that can be ‘understood' by the cortical neurons. Flexible arrays with penetrating electrodes have been developed (Utah Electrode Array [47]) that have been tested in various animals including monkeys. It is, however, not yet clear to which extent such approaches can provide useful vision.…”

Sight Restoration Comes into Focus: Versions of Visual Prostheses

“…Currently, a University of Utah research team under the leadership of Bradley Greger, Ph.D., assistant professor in bioengineering, is conducting tests of the cortical version of the Utah Electrode Array [5]. For this work, monkeys are trained to fixate on a small illuminated spot in the middle of a computer screen, and indicate when they notice a second small point of light elsewhere on the screen.…”