Researchers are already using brain-computer interfaces to aid the disabled, treat diseases like Parkinson's and Alzheimer's, and provide therapy for depression and post-traumatic stress disorder. Work is under way on devices that may eventually let you communicate with friends telepathically, give you superhuman hearing and vision or even let you download data directly into your brain, a la The Matrix." Researchers are practically giddy over the prospects. "We don't know what the limits are yet," says Melody Moore Jackson, director of Georgia Tech University's BrainLab. At the root of all this technology is the 3-pound generator we all carry in our head. It produces electricity at the microvolt level. But the signals are strong enough to move robots, wheelchairs and prosthetic limbs -- with the help of an external processor. One of the more controversial uses under development is telepathy. It would require at least two people to be implanted with electrodes that send and receive signals. DARPA, the Pentagon's technology research division, is currently working on an initiative called "Silent Talk," which would let soldiers on secret missions communicate with their thoughts alone. This stealth component is attractive, but naysayers fear that such soldiers could become manipulated for evil means.