The fitting of replacement robotic hands to the three Austrian men who had lost function as a result of accidents is a marvellous achievement. It is not the first time, however, that missing limbs have been bionically reconstructed.
A US soldier’s arm and hand were replaced with mind-controlled robotic versions in December 2013, and in 2011 a combined robotic arm and hand was developed and tested. It provided 22 degrees of movement, compared with the 30 normal in an undamaged limb.
The return home of soldiers from Iraq and, later, Afghanistan with missing limbs has driven much of the investment and innovation in these bionic reconstructions. Similar efforts involving a much lower level of technology came after the world wars.
The robotic arm developed in 2011 arose as a result of the “revolutionising prosthetics” programme run by the US Defense Advanced Research Projects Agency. This month Darpa signed contracts with commercial companies to develop an even more advanced replacement hand, one with a sense of touch that provides a sensory response for the wearer.
A breakthrough in mind control of a robotic arm came in 2008, when Andrew Schwartz, at the University of Pittsburgh, trained two rhesus monkeys to operate a robotic arm that could deliver food treats using thought alone.
The mind control was delivered via electrodes implanted in the brains of the macaques. The electrodes picked up electrical signals in the part of the brain controlling movement.
The human replacement hands and arms use a different approach: electrodes on the skin can read the tiny electrical signals that nerves produce.
The nerves are like wires that carry electrical signals from the brain out to the limbs and extremities, with the signals triggered by thought. The muscles are like motors that can drive movement when stimulated by the nerves.
If the nerves are severed the connection is broken, and signals no longer reach the muscles, but the brain does not know this – and continues to send signals triggered by thought.
An artificial connection can be made, however, by using a sensor to pick up the signal coming down the undamaged part of the nerve. The signal can in turn be used to trigger electric motors in the bionic hand or arm, with the subject learning how to control this movement through weeks or even months of training.
Only a few nerves are needed to control this, but the macaque research shows there is a different way. Prof Schwartz is connecting electrodes to 100 locations in the brain, to deliver much more refined movements controlled completely by thought.