Rhesus monkeys have been taught to control a robot arm using brain signals alone.
The monkeys adapted quickly
Researchers at Duke University Medical Center in North Carolina said the animals appeared to operate the robot arm as if it were their own limb.
They believe the finding could eventually lead to the development of highly sophisticated false limbs for people who are paralysed.
The technology may also aid people with stroke and spinal cord damage.
The Duke team implanted an array of microelectrodes into the brains of two female rhesus macaque monkeys. They implanted 96 electrodes in one animal and 320 in the other.
They then analysed the signals given off by the electrodes as the animals were taught to use a joystick to both position a cursor over a target on a video screen and to grasp the joystick.
After the animals' initial training, however, the researchers made the cursor more than a simple display - they invested it with the physical characteristics of a robot arm functioning in another room.
The animals' performance initially declined when the experiment was made more complex - but they quickly learned to allow for the changes, and became proficient in manipulating the robot-reflecting cursor.
The scientists next removed the joystick, after which the monkeys continued to move their arms in mid-air to manipulate and "grab" the cursor, thus controlling the robot arm.
After only a few days of playing with the robot arm in this way, one of the monkeys realised that she did not need to move her arm at all.
She kept her arm at her side, and controlled the robot arm using only her brain and visual feedback.
Researcher Professor Miguel Nicolelis said: "Our analyses of the brain signals showed that the animal learned to assimilate the robot arm into her brain as if it was her own arm."
Professor Nicolelis said the finding raised the possibility of developing prosthetic devices for paralysed people which could be operated by brain signals alone.
He said: "There is certainly a great deal of science and engineering to be done to develop this technology and to create systems that can be used safely in humans.
"However, the results so far lead us to believe that these brain-machine interfaces hold enormous promise for restoring function to paralysed people."
The researchers are already analysing the brain signals of human subjects to determine whether they correlate with those seen in the animal experiments.
John Cavanagh, of the UK charity Spinal Research, said the latest study, and others of a similar ilk, were providing a great insight into how the brain is able to adapt itself to new situations.
He told BBC News Online: "If sense can be made of brain-derived signals using a computer interface, and in turn the brain can learn how to fine-tune the interaction, then almost any external device could be controlled.
"In this case the computer was linked to a mechanical arm, but it could be to steer a vehicle, operate domestic equipment, answer the telephone, control computer equipment, whatever is appropriate to the patient's disability."
However, he warned that implanting electrodes into the brain was a highly invasive procedure.
"One would need to be absolutely sure that the appropriate sites are being used and that no damage was being done to the patient in the long-term."
The research is published in the journal Public Library of Science Biology.