Patients implanted with a visual cortical prosthesis were able to interpret letters “traced” on the visual cortex in a manner similar to tracing letters on the palm by stimulating electrodes in a dynamic sequence, researchers at Baylor College of Medicine and the University of California, Los Angeles, found. Their work appeared in the May 2020 edition of Cell.
The scientists used a technique known as current steering—passing current through two adjacent electrodes to create a virtual electrode between them—to stimulate the visual cortex in a continuous trajectory.
Varying the amount of current delivered to adjacent electrodes allowed the virtual electrode to be positioned at different locations along the path.
Many previous studies of retinal prostheses used electrical stimulation delivered in a regular sequence of stimulated electrodes, rather than activation of all electrodes at once, to reduce the likelihood of epileptic seizures, the study authors said. Dynamic current steering differs in that the pattern of sequential stimulation is related to the form that is being conveyed to the participant, rather than a fixed order.
The study had five subjects—two blind subjects already participating in studies related to the Orion Visual Cortical Prosthesis System, and three sighted subjects being monitored with electrodes for epilepsy. Additional research electrodes were implanted and stimulated for this study.
Subjects were able to reliably discriminate letter forms from a small number of electrodes without training—a feat that would have been impossible with static stimulation, or all electrodes stimulated at the same time, the researchers said.