Implants buried deep in the brain may be the best hope yet for building bionic eyes to restore vision.
Most visual prosthetics rely on implants behind the retina, which stimulate nerve cells and generate visual sensations or phosphenes in the brain. Such prosthetics require a detailed map of where phosphenes will appear in the person鈥檚 brain in response to electrical stimulation of a given nerve cell. Once the map is complete, partly through trial and error, digital images can be converted into electrical pulses that allow blind people to 鈥渟ee鈥�.
In patients with severe eye damage, however, there are not always enough surviving retinal neurons to stimulate, and the retina can further degenerate over time. An alternative is to implant electrodes directly into the visual cortex, but this is a large and complex area, making the procedure difficult.
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Now John Pezaris and R. Clay Reid at Harvard Medical School are investigating implanting electrodes in the lateral geniculate nucleus, the area of the thalamus that relays visual signals from the retina to the visual cortex. It can be reached via a small incision in the skull.
The researchers implanted electrodes into the geniculate regions of two macaques trained to gaze at a point of light on a computer screen. When stimulated by the electrodes, the monkeys directed their gaze to a spot in front of them predicted by maps of the geniculate region. Their response was exactly the same as when they were shown a flash of light on the screen ().
