Scientists have created bionic monkeys by perfecting a device that allows the animals to move robotic arms through the power of thought.

Dr Andrew Schwartz and his team at the University of Pittsburgh told Nature that they have built a successful brain-machine interface which uses small implants in the base of the brain to control the robotic arm.

The team has produced a video of the animals using the arm to feed themselves with a success rate of around 70 per cent. Their control was so fine that the monkeys could also navigate the arm around obstacles to get to the food.

The monkeys were first taught to control the arm using joysticks so that the brain impulses used in the task could be mapped. They then had their arms restrained and had to use brain power alone.

Dr Schwartz explained that the work will be used to give severely disabled people a better quality of life, and that trials with humans are being planned.

"I think we will be doing this on an experimental basis in two years," he said. "The biggest stumbling block is that the electrodes are fragile. They also become embedded in the brain and scar tissue forms around them."

Once these difficulties are overcome Dr Schwartz believes that human interfaces could be built which would last for decades.