Most amputees lack proprioception—the ability of your brain and nervous system working together based on your intent. Many upper-limb amputees are unable to gauge how their prosthetic is moving without visually tracking it—the nervous system and brain do not work properly together to provide proprioceptive feedback. Unfortunately, without this feedback, even the most advanced prosthetic limbs remain numb to the user.

The Defense Advanced Research Projects Agency’s (DARPA) Biological Technologies Office (BTO) has created the first program to aid amputees beyond previous prosthetics work. Called “Hand Proprioception and Touch Interfaces” (HAPTIX), the program will require not only scientists and engineers, but psychologists as well.

According to Doug Weber, DARPA program manager, the information-rich peripheral nerves are accessible targets for combining with the nervous system. Even when a limb is amputated, these nerves still maintain motor and sensory fibers that can function again with assistance.

That motor/sensory capability forms the foundation for HAPTIX: The system will attempt to infiltrate the biological communication pathway so that the same control over hands and arms through the neural signal pathway can be used for prosthesis. HAPTIX aims to deliver natural sensations to amputees, allowing for dexterous, intuitive control of prosthetics, as well as provide the physiological benefit of prosthetic “embodiment” and reduce pain of the amputation site. The program will build on DARPA’s previous program, Revolutionizing Prosthetics and Reliable Neutral-Interface Technology (RE-NET). 

HAPTIX researchers hope to achieve multiple goals: develop interface systems to measure motor signals in peripheral nerves; use a prosthetic limb system from RE-NET and adapt it to incorporate sensors that provide proprioceptive feedback to the user; and create a fully implantable device that’s safe, effective, and reliable for humans. However, one key challenge stands in the way of these goals. Researchers must determine stimulation patterning strategies that draw out natural sensations of touch and movement.

The program will end with a 12-month, take-home trial of the HAPTIX prosthesis system. The physical and psychological benefits to the program could be enormous; for example, improving prosthesis “embodiment” and lessening phantom limb pain suffered by 80% of amputees.