A BRAIN-MACHINE INTERFACE might someday help a patient whose limbs have been paralyzed by a spine injury. Tiny arrays of microwires implanted in multiple motor cortex areas of the brain would be wired to a neurochip in the skull. As the person imagined her paralyzed arm moving in a particular way, such as reaching out for food on a table, the chip would convert the thoughts into a train of radio-frequency signals and send them wirelessly to a small battery-operated "backpack" computer hanging from the chair.

The computer would convert the signals into motor commands and dispatch them, again wirelessly, to a different chip implanted in the person's arm. This second chip would stimulate nerves needed to move the arm muscles in the desired fashion. Alternatively, the backpack computer could control the wheelchair's motor and steering directly, as the person envisioned where she wanted the chair to roll. Or the computer could send signals to a robotic arm if a natural arm were missing or to a robot arm mounted on a chair. Patrick D. Wolf of Duke University has built a prototype neurochip and backpack, as envisioned here.

   
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