Two other patients in the trial, both with different types of injuries, also learned to manipulate a computer program, although they have not yet tried the robotic arm. "The results show it's feasible to use these devices in a real world setting, but we've got a long way to go before everyday use," says Donohue.

Neuroscientists have used similar devices in monkeys and other animals for several years, but Donohue's trial is the first to test surgically implanted electrode arrays in human patients. "It's a big leap to bring this technology into humans," says Stephen Scott, a neuroscientist at Queen's University in Kingston, Ontario, who wrote a commentary accompanying the paper. "This was pretty successful for a first attempt -- the patients showed some impressive capabilities."

While the results are promising, experts caution the technology is in the early stages. "This is still far from being a useful device that actually increases the quality of life for this patient," says Andrew Schwartz, a neuroscientist at the University of Pittsburg who studies similar devices in animals. The same technology works better in monkeys, suggesting that more work needs to be done in designing the recording electrodes and software filters, he says.

Currently, available assistive devices for paralyzed patients, such as computer programs activated by voice or eye movements, rely on a secondary signal to carry out the command, and require both a training period and a high level of concentration. An implanted device has the potential to aid patients in a much more natural way. It "taps into all the information the brain uses to move [the muscles]," says Donoghue. Because it mimics the brain's normal processing system, patients can control a cursor and talk at the same time, he says.

Donoghue and colleagues are now adapting the experimental system into a device for broader use. The current system has wires connecting the implant to an external computer through the skull, which carries the risk of infection. The researchers plan to miniaturize the hardware and make it wireless, so the entire system can be implanted.