Researchers at Stanford University say that they used electrical stimulation of retinal cells to produce the same patterns of activity that occur when the retina sees a moving object. They say that this is a step toward restoring natural, high-fidelity vision to blind people.

By targeting specific cells in the retina, the neural tissue at the back of the eye that converts light into electrical activity, they have been able to reproduce natural patterns of activity in the retina with exquisite precision.

Natural vision, including the ability to see details in shape, color, depth and motion, requires activating the right cells at the right time. The new research shows that patterned electrical stimulation is able to do that in isolated retinal tissue, particularly, a type of retinal ganglion cell called parasol cells. These cells are needed for detecting movement, and its direction and speed, within a visual scene. When a moving object passes through visual space, the cells are activated in waves across the retina.

The researchers placed patches of retina on a 61-electrode grid. Then they sent out pulses at each of the electrodes and listened for cells to respond, almost like sonar. This enabled them to identify parasol cells, which have distinct responses from other retinal ganglion cells. It also established the amount of stimulation required to activate each of the cells. Next, the researchers recorded the cells' responses to a simple moving image—a white bar passing over a gray background. Finally, they electrically stimulated the cells in this same pattern, at the required strengths. They were able to reproduce the same waves of parasol cell activity that they observed with the moving image.

While, they say, there is still is a long way to go between their results and making a device that produces meaningful, patterned activity over a large region of the retina in a human patient, they are learning to speak to the nervous system in its own language, and may someday be able to precisely reproduce its normal function.

Such advances could help make artificial vision more natural, and could be applied to other types of prosthetic devices, too, such as those being studied to help paralyzed individuals regain movement, they added.

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