Raising the stakes for cortical visual prostheses

Abstract

In this issue of the JCI, the dream of restoring useful vision to blind individuals with neurotechnology moves one step closer to realization. Fernández et al. implanted an electrode array with 96 penetrating electrodes in the visual cortex of a blind patient who had been without light perception for 16 years due to optic neuropathy. Remarkably, the patient was able to perceive visual patterns created by passing current through array electrodes. The use of a penetrating electrode array meant that action potentials from single neurons could be recorded to study the neural response to stimulation. Compared with electrodes resting on the cortical surface, penetrating electrodes require one-tenth the current to create a visual percept. However, patterned electrical stimulation often fails to produce the expected percept for penetrating and surface electrode arrays, highlighting the need for further research to untangle the relationship between stimulus and perception.

Figure 1. Stimulation of the Utah array in the visual cortex of a blind subject resulted in visual percepts.

(A) A Utah electrode array was implanted near the occipital pole in early visual cortex. Stimulation of a single electrode in the array (blue square) produces the percept of a single bright phosphene in the visual field (blue circle). Percept data are based on Fernandez et al. (8). (B) Percepts produced by stimulating single electrodes lie within the lower left visual field. However, the fine structure of the phosphene locations was disorganized. Stimulation of single electrodes along a column of the electrode array led to a disorderly progression of phosphenes in visual space (colored circles with connecting lines; color indicates correspondence between stimulated electrode and phosphene location, not phosphene colors). (C) Simultaneous stimulation of multiple electrodes produced varying results. Some stimulation patterns produced recognizable letters (top) or coherent lines in visual space (bottom). (D) Some stimulation patterns containing neighboring electrodes produced multiple discrete phosphenes. (E) Some stimulation patterns containing noncontiguous groups of electrodes resulted in single percepts of a horizontal line (top, blue electrodes), a vertical line (top, red electrodes), or a letter (bottom). (F) Some stimulation patterns failed to produce recognizable percepts.