A man paralysed from the neck down has shown he can open email, control a TV and move objects with a robotic arm by thought alone.
The 25-year-old American patient, Matthew Nagle, had a computerlinked implant placed in his brain that enabled him to operate devices just by thinking about it.
Brain-computer inter-faces have been demonstrated before, in humans and animals. But this is the biggest step taken so far towards developing "bionic" systems that can restore motor function in people who have lost control of their limbs.
In the 1970s TV series The Six Million Dollar Man, scientists rebuilt the body of crash victim Steve Austin with bionic prosthetics controlled by his mind.
At the time the concept was pure fantasy, but in future thought-controlled replacement limbs could be made real.
The results described yesterday in the journal Nature represent decades of work.
However the scientists involved in the research stress that the technology is still in its infancy.
Mr Nagle, from Massachusetts, whose spinal cord was severed in 2001, received his implant at Rhode Island Hospital in 2004.
Known as the BrainGate Neural Interface System, it consists of an array of electrodes that record neural activity from the motor cortex of the brain.
Signals from the implant are decoded and processed by a computer, allowing them to be translated into movement commands.