Filling in the Visual Gaps: Shifting Cortical Activity using Current Steering.

Cortical vision prostheses are being developed to restore sight in blind patients. Existing electrode arrays that electrically stimulate cortical tissue to artificially induce neural activity are difficult to position directly next to each other. Leaving space between implants creates gaps in the visual field where no visual percepts can be created. Here, we propose current steering as a solution to elicit a neural response between physical electrode locations. We assessed the centroid of neural activity produced by dual-electrode stimulation in the visual cortex of Sprague-Dawley rats. We determined that this centroid could be shifted between physical electrodes by altering the ratio of charge delivered to each electrode. This centroidal shift could enable better environmental perception for cortical implant patients by creating a complete visual field representation while maintaining safe array spacing.

Local field potential phase modulates neural responses to intracortical electrical stimulation.

Cortical visual prostheses could one day help restore sight to the blind by targeting the visual cortex with electrical stimulation. However, power consumption and limited spatial resolution impose limits on performance, while large amounts of electrical charge sometimes necessary to evoke phosphenes can cause seizures. Here, we propose the use of the local field potential as a control signal for the timing of stimulation to reduce charge requirements. In Sprague-Dawley rats, visual cortex was electrically stimulated at random times, and neural responses recorded. Electrical stimulation at specific phases of the local field potential required smaller amounts of charge to elicit spikes than naïve stimulation. Incorporating this into prosthesis design could improve their safety and efficacy.