Monkeys can control a robot arm as naturally as their own limbs using only brain signals, a pioneering experiment has shown. The macaque monkeys could reach and grasp with the same precision as their own hand.
"It's just as if they have a representation of a third arm," says project leader Miguel Nicolelis, at Duke University in Durham, North Carolina. Experts believe the experiment's success bodes well for future devices for humans that are controlled solely by thought.
One such type of device is a neurally-controlled prosthetic - a brain-controlled false limb. Nicolelis says his team's work is important because it has shown that prosthetics can only deliver precision movements if multiple parts of the brain are monitored and visual feedback is provided.
Gerald Loeb, a biomedical engineer at the University of Southern California in Los Angeles, says the new experiment already has some parallels in everyday life. For example, he says, when you drive a car it becomes an extension of your body.
But Nicolelis says the monkeys appeared to be treating the robot arm as their limb, not an extension. "The properties of the robot were being assimilated as if they were a property of the animal's own body."
The core of the new work is the neuronal model created by the researchers. This translates the brain signals from the monkey into movements of the robot arm. It was developed by monitoring normal brain and muscle activity as the monkey moved its own arms.
The task involved using a joystick to move a cursor on a computer screen. While the monkey was doing this, readings were taken from a few hundred neurons in the frontal and parietal regions of the brain. The activation of the biceps and wrist muscles was monitored, as was the velocity of the arms and the force of the grip.
Once the neuronal model had developed an accurate level of prediction the researchers switched the control of the cursor from the joystick to the robotic arm, which in turn was controlled by the monkey's brain signals. At first the monkeys continued moving their own arms whilst carrying out the task, but in time they learned this was no longer necessary and stopped doing so (see Flash animation.
For Nicolelis, the end goal is to help people with paralysis by bypassing brain lesions or damaged parts of the spine. Initially patients would control robotic aids, such as a mechanical arm attached to a wheelchair.
But eventually the signals could be used to stimulate the nerves controlling a patient's own muscles. Nicolelis and his team have already begun to testing this approach on people, but he says it is too early to discuss this research.