Monkeys were trained to command the robot arm to feed themselves marshmallows. Video Credit: Velliste et al./Nature

Researchers in the United States have created a brain implant that allows monkeys to feed themselves using a robotic arm just by thinking about it. The device could one day help paralysed people to operate prosthetic limbs that might enable them to eat, drink or use other utensils for themselves.

This video shows a macaque monkey successfully using the robotic arm to grab pieces of marshmallow off a pin positioned at various different locations. The arm is engineered to move in a 'realistic way', with a range of shoulder movements, an elbow that moves in just one direction and a simple claw grip to simulate a grabbing hand.

The arm is controlled by a network of tiny electrodes called a brain–machine interface, implanted into the motor cortex of the monkeys' brains — the region that controls movement. It picks up the signals of brain cells as they generate commands to move, and converts those into directional signals for the robotic arm.

The researchers, led by Andrew Schwartz of the University of Pittsburgh, Pennsylvania, first trained two monkeys to use a joystick to manipulate the arm. Then, the monkeys' own arms were restrained by placing them in tubes, and the robotic arm was switched over to brain control.

As the researchers report in Nature1, the two monkeys achieved success rates of 61% and 78%, respectively. And they could also direct the arm around obstacles to ensure safe delivery of the food morsels, which included fruit such as grapes.

A human interface

Schwartz believes that it won't be long before the technology is tested in humans, although he predicts that it will be longer before the devices are used in actual patients with disabilities. "I think we'll be doing this on an experimental basis in two years," he says.

Brain interfaces are not particularly new — human versions have been around for several years (see 'Computer users move themselves with the mind'). But this is the first time a brain–machine interface has been used to fulfil a useful function — in this case, allowing the monkeys to feed themselves. "Up until now, almost all demonstrations [of the technology] have been in a virtual world," Schwartz says.

Successfully developing these brain implants for humans will require more resilient, long-lasting electrodes, Schwartz adds. "The biggest stumbling-block is that the electrodes are fragile, and also they become embedded in the brain and scar tissue forms around them." Beating these problems will allow technicians to develop brain interfaces that could potentially last for years or even decades.