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with movements of his face and neck. Finally, Ray was able to accu- rately place the cursor wherever he wanted to with no bodily motion at all, which showed that he was controlling the cursor with his brain. When Ray reached this point, Kennedy asked him what he thought about as he moved the cursor. Rays reply (spelled out letter by letter with the cursor) was that he thought only about moving the cursor and not about any part of his body; so from Rays own viewpoint, he moved the cursor by mind alone.

One of the more interesting results of this feat relates to how the electrodes interact with the plasticity of the brain. Kennedy interprets his results as showing that as Ray was trained, the implanted hand cortexchanged to cursor cortex,devoted only to cursor move- ment. Based on his work with monkeys, Nicolelis makes a similar point:

Long-term operation of [a neurally controlled prosthesis] by paralyzed subjects would . . . through a process of cortical plasticity . . . confer to subjects the perception that such apparatus has become an integral part of their own bodies.

If human neurons actually adapt themselves in this way, that offers another potential benefit to patients;it gives great freedom as to where electrodes can be placed in the brain, regardless of where the brain is damaged. Changes in the brain due to neural interfacing might have other implications, too, that warrant careful consideration.

Although implanted electrodes enable a brain to communicate with the exterior world, efforts also continue to forge BMI connec- tions that do not need surgery. One such BMI technology being pur- sued under DARPA auspices is based on magnetic effects.According to DARPA, the aim is to communicate with the world directly through brain integration with peripheral devices and systems.For example, pilots could control aircraft just by thinking about how they want them to move (as in the 1977 novel, Firefox, by Craig Thomas, and the 1982 film of the same name) or an infantryman could operate a powered exoskeleton. It has been known for some time that neural activity produces magnetic fields that extend through the skull and can be measured by sensitive detectors. Many questions remain,

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