A prosthetic arm or leg controlled entirely by brain input – it’s already been done, crudely, with monkeys. Trials are coming this summer for humans to manipulate a robotic arm with only their thoughts.

The arm itself is indeed a sleek piece of work, a technological wonder. Says its creators, it “has function almost identical to a natural limb in terms of motor control and dexterity, sensory feedback (including proprioception), weight, and environmental resilience.”

This work is a collaboration of engineers and biologists funded by the engineering toybox for national security and future war fighting — with an annual budget of $3.2 billion — the Defense Advanced Research Projects Agency (DARPA).

DARPA’s mission: “…to maintain the technological superiority of the U.S. military and prevent technological surprise from harming our national security by sponsoring revolutionary, high-payoff research bridging the gap between fundamental discoveries and their military use.”

The M-16 rifle, the Stealth Bomber and the Internet came out of DARPA. One wonders how prosthetics left the realm of rehab to fit in to the world of security and defense (future robot-avatars wirelessly controlled by soldiers, kind of a real life video game), but this is no small program.

The prosthetic arm in the coming human brain-control tests is from Johns Hopkins University’s Applied Physics Laboratory (APL) in Laurel, MD. In 2006 the lab was awarded a $30.4 million contract for the first phase of Revolutionizing Prosthetics, with a goal of developing a “next-generation mechanical arm that mimics the properties and sensory perception of the real thing.”

APL delivered the arm; last year DARPA awarded the Hopkins team up to $34.5 million more to manage development and testing of the arm, now called the Modular Prosthetic Limb (MPL). A consortium of engineers from Caltech, University of Pittsburgh, University of Utah and the University of Chicago are moving the technology forward to test it on human subjects, using some sort of brain-controlled interface.

Here’s what DARPA predicts:

The Revolutionizing Prosthetics program will create a fully functional (motor and sensory) upper limb that responds to direct neural control, within this decade. This revolution will occur by capitalizing on previous DARPA investments in neuroscience, robotics, sensors, power systems, and actuation. In particular, this program builds on DARPA's Human-Assisted Neural Devices program, which recently decoded the brain's motor signals with such fidelity that movements of a robotic arm can be controlled entirely by direct brain control.

A major challenge ahead is figuring out how best to jack into the brain to retrieve the signals that will control the arm. DARPA gave the University of Pittsburgh $6 million last month to test implanted electrodes that harvest the signals. Engineers at Pitt did much of the work with monkeys and have worked out basic software to decode the signals for brain-controlled prosthetics.

Beginning this summer, an array of 16 electrodes will be placed on the brain surfaces of three patients to test using their brain waves to control a computer cursor and then the prosthetic arm. In another part of the trial, two 100-electrode arrays will be placed on the motor cortex of three patients; this work will be done over the next three years.

One array will pick up brain signals that control the arm, the other will get input from a region that controls the wrist and hand. The idea is to eventually avoid wires, but for now, the signals will be channeled through wires from the skull to a computer, which will then direct the prosthetic arm.

Mike Boninger, one of the Pitt scientists, said these sorts of implants might also allow paralyzed people to control their own limbs through a muscle-stimulating device. "When I think of next steps," he said, "I'm thinking of something that isn't visible to the rest of the population and is able to allow a patient to use his own arm with multiple degrees of freedom."

By Sam Maddox