To understand the meaning of “proprioception,” try a simple experiment. Close your eyes and lift your right arm above your head. Then, move it down so that it’s parallel to the ground. Make a fist and release it. Move it forward, and then swing it around behind you like you’re stretching. Finally, freeze in place, open your eyes, and look. Is your arm positioned where you thought it would be?

For most people, the answer will be, “Yes.” That’s because your brain and nervous system worked together to move your body according to your intent and processed the sensory feedback to know where your arm was in space despite not being able to visually track it.

For many upper-limb amputees using prosthetic devices, the answer would be, “No.” They wouldn’t have confidence that their device would be where they think it is because current prostheses lack provisions for providing complex tactile and proprioceptive feedback to the user. Without this feedback, even the most advanced prosthetic limbs will remain numb to the user and manipulation functions will be impaired.

The Defense Advanced Research Projects Agency’s (DARPA) new hand proprioception and touch interfaces (HAPTIX) programme seeks to deliver those kinds of naturalistic sensations to amputees, and in the process, enable intuitive, dexterous control of advanced prosthetic devices that substitute for amputated limbs, provide the psychological benefit of improving prosthesis “embodiment,” and reduce phantom limb pain. The programme builds on neural-interface technologies advanced during DARPA’s Revolutionising Prosthetics and Reliable Neural-Interface Technology (RENET) programmes that made major steps forward in providing a direct and powerful link between user intent and prosthesis control.

HAPTIX aims to achieve its goals by developing interface systems that measure and decode motor signals recorded in peripheral nerves and/or muscles. The programme will adapt one of the advanced prosthetic limb systems developed under Revolutionising Prosthetics to incorporate sensors that provide tactile and proprioceptive feedback to the user, delivered through patterned stimulation of sensory pathways in the peripheral nerve. One of the key challenges will be to identify stimulation patterning strategies that elicit naturalistic sensations of touch and movement. The ultimate goal is to create a fully-implantable device that is safe, reliable, effective, and approved for human use.

“Peripheral nerves are information-rich and readily accessible targets for interfacing with the human nervous system. Research performed under DARPA’s RE-NET programme and elsewhere showed that these nerves maintain motor and sensory fibres that previously innervated the amputated limb, and that these fibres remain functional for decades after limb loss,” said Doug Weber, the DARPA Program Manager. “HAPTIX will try to tap in to these biological communication pathways so that users can control and sense the prosthesis via the same neural signaling pathways used for intact hands and arms.”