In a dramatic display of the potential of prosthetic arms, a monkey at the University of Pittsburgh was able to use his brain to directly control a robotic arm and feed himself a marshmallow.

To achieve the feat, two monkeys had a grid of microelectrodes implanted into the motor cortex, part of the brain that controls motor planning and execution. The animals had previously been trained to move an anthropomorphic robotic arm, with moveable joints at the shoulder, elbow, and wrist, using a joystick.

To learn to control the prosthesis with their minds, the monkeys had their arms temporarily restrained as they watched a computer move the arm through the required motions–to extend the arm to the piece of food, grip it, bring it to the mouth, and release it. “They imagine themselves doing the task, like athletes do for sports,” says neuroscientist Andrew Schwartz. “The neurons are active as they observe the movement, and then we can capture the [neural signals] and use them for our own control.”

The researchers aim to test fully implanted electrodes, like those used in the monkey to control the robotic arm, in humans within the next two years, to aid patients who are completely paralyzed.