Prosthetic touch sense

For the average person, the loss of a hand or arm can be an enormous physical and emotional challenge. Unfortunately, our military forces have to deal with this problem far too often. For this reason, the Defense Advanced Research Projects Agency (DARPA) spends a lot of time and money on research into prosthetic limbs. The devices for legs have progressed rapidly in recent years, but hands and arms pose special challenges. Not only do these require finer control of complex motions, but they also need to provide feedback to the wearer to replace the lost physical sensation of touch.

DARPA recently reported on a research project that provides connections to the subject’s brain, not just for control of the artificial limb, but also to sense when the hand comes in contact with objects. The physical control has been done before, but this study represents an important advance in closing the loop by providing touch. An array of electrodes was placed on the subject’s motor cortex (the part that controls muscle movement), and another array was placed on the sensory cortex (the part that receives touch sensations from the nerves). The subject was able to control the mechanical hand using thoughts, but was also able to sense when the hand was in contact with objects. The subject could even tell when one of the fingers was being touched lightly.

Rather than use sensors on the surface of the hand, the system relies on sophisticated torque sensors in the joints to detect pressure. In blindfolded tests, the subject was able to identify which finger was being touch with nearly 100% accuracy. This is an important step to close the feedback loop between brain and prosthetic. We may be getting closer to Steve Austin faster than we realize.