An implant packed with more than 1000 tiny, brain-stimulating electrodes generates recognizable perceptions of motion and complex shapes - including letters of the alphabet - in a monkey's mind. The new study provides a proof-of-concept for using electrical microstimulation of the visual cortex to create a form of artificial vision. While several technical hurdles remain to be overcome before human cortical visual prostheses (CVPs) become viable, the findings offer hope that the devices may one day bring useful visual function to the more than 40 million people living with blindness worldwide. Experiments in both humans and animals have shown that electrical stimulation of the visual cortex can reliably create the perception of a brief, bright flash of light, also known as a phosphene, which is perceived in specific locations and sizes according to the neurons that are stimulated. This premise has formed the basis of designs for CVPs, which would ideally convert camera footage into patterned brain stimulation to create a form of artificial vision perception in the blind. However, many studies have been limited by electrodes' position and power requirements, greatly reducing the number that can safely be stimulated simultaneously, which allows only for relatively simple phosphene percepts to be evoked. Here, Xing Chen and colleagues report a high-definition neuroprosthesis containing 1024 intracortical electrodes arranged in a matrix-like pattern. To test the system, Chen et al. implanted the device into the visual cortex of two macaque monkeys trained to recognize specific shapes, including letters. Then, by simultaneously stimulating hundreds of electrodes, the authors recreated the shapes in the monkey's perception using phosphenes and found that the animals immediately recognized them as if they were visually presented. "Chen et al. set a new benchmark for the next generation of CVPs by demonstrating that 1000 electrodes are sufficient to create percepts of letters, orientation and motion," write Michael Beauchamp and Daniel Yoshor in a related Perspective.
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Science