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cortex or in the peripheral system with an interface that converts them into electrical signals that can control a prosthetic hand (or any device), and, working in the opposite direction, that accepts electrical pulses from the hand (for instance from tactile sensors) and converts them into meaningful neural signals for the brain.

The technique explored by Darios group is one of several used or proposed for such electroneural interfacing and relies on an inter- face implanted into the peripheral nervous system.This approach uses a so-called regeneration type of neural interface, which blends tech- niques from electrophysiology and from the well-established nanotechnology used to manufacture silicon computer chips. Silicon is a good material for implantation because it seems to be nontoxic and has the necessary mechanical and electrical characteristics.Also, it can be readily manipulated by using state-of-the-art chip technology at the small scale of the human nerves.

The interface unit begins with a minute square of silicon 1.5 millimeters (0.06 inches) on a side.A set of metal electrodes is depos- ited on the surface of the chip, and further processing produces an array of tiny square holes, measuring only thousandths of an inch across, that pierce the chip.Then the whole chip, now called a die, is placed within a small conduit made of a nontoxic plastic that will not deteriorate inside a living body.The electroneural connection is ac- complished by cutting a specific nerve and letting it regenerate within the plastic conduit. Nerve fibers reconnect themselves through the holes in the die,bringing them near the electrodes,so that current can flow in both directions between nerve and electrodes.Tests in which the interfaces were installed in rabbits showed that the interchange of current works: Signals originating in the nerve were detected in wires attached to the electrodes on the die, and external electrical signals sent to the electrodes affected the nerve,making the rabbits leg twitch.

For all the preliminary success of the rabbit experiments, serious obstacles stand in the way of extending the technique to humans.The neural signals are small and full of extraneous noise. They require complex processing to interpret correctly, and it has not yet been shown that the signals could actually control an artificial hand. On the

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