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Restoring Vision
The next field poised to make a leap forward concerns vision. Researchers are progressing with several approaches toward transmitting information from outside the body to the part of the brain responsible for vision -- the visual cortex. With the goal of restoring limited vision to the blind, the technology involves the use of tiny chips and wires attached to delicate tissue such as the retina and the visual cortex, converting light into electrical impulses that can be interpreted as images.

When light hits the retina at the back of the eye, it is registered by more than one million rods and cones, which convert the light wave into an electrical signal. The signal is passed back through the retina's sheets, compressed and altered as it moves from neuron to neuron, and eventually gathered up and sent along the optic nerve to the visual cortex. At the visual cortex, this compressed, scrambled sequence known as the neural code is, amazingly, reassembled into an image the brain can understand.

Retinal Prostheses
Due to the complexity of this process, some researchers believe visual prosthetics must incorporate the retinal neurons -- in other words, design a system that allows these retinal cells to do the work they normally do. One artificial retina being tested at the University of Southern California by Eugene De Juan and Mark Humayun is a wafer-thin grid consisting of 16 electrodes that is implanted in the eye. The patient wears a special set of glasses with a miniature camera on the front. When this person "looks" at an object, images received by the camera are processed by a wallet-sized computer and converted into impulses that stimulate the electrode grid. From that point, the impulses are carried on the optic nerve back to the brain as if the retina were still functioning.

This device could be effective for a visually impaired person whose damage or disease was confined to the rods and cones, such as macular degeneration (which could affect an estimated 2.5 million Americans by 2020), or retinitis pigmentosa. It would not be much help against common eye disorders like cataracts, which affect the lens, or glaucoma, which damages the optic nerve.

Researchers Vincent Chow and Alan Chow, at a company called Optobionics, are developing a wireless microchip with thousands of tiny photoelectric cells, which, they maintain, can convert light passing through the eye into electrical pulses in the retina. Such a device would be far less cumbersome than other visual prosthetics (attached to the retina, it is thinner than a human hair and there are no wires). However, other scientists are skeptical it could ever work; they argue that since the microchip does not contain any type of battery or amplifier, the weak energy provided by the light received by the device would not generate sufficient power to activate the nerve cells and transmit images.

Direct to the Brain
Other approaches bypass the eyes completely. As featured in "Human Body Shop," a team in Portugal, led by William Dobelle, uses a small camera mounted on eyeglasses, but the signals received by the camera are carried by wires through two computers and then to electrodes actually mounted on the surface of the visual cortex. When the cortex receives an impulse, the wearer of the device sees a point of light called a phosphene. (These are the bits of light that seem to appear when you rub your eyes or bump your head). If several points on the cortex are stimulated, multiple phosphenes can be perceived like a string of lights that could represent the rough outline of an object. The apparatus is designed so that if the camera registers something on the right side of its frame, the sightless person wearing the device will perceive something in roughly the same position.

Richard Normann, at the University of Utah, is taking a similar approach, but the electrodes are tiny microneedles implanted in the brain rather than on the surface. While this has potential for sharper vision, it also is more invasive and so far has been tested only in animals.

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brain surgery
Doctors in Portugal implant an electrode onto a patient's brain.
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man with monkey
Neuroscientist Miguel Nicolelis of Duke University has trained monkeys implanted with neuroprosthetics to move robotic arms.
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