A neurally-controlled arm and hand prosthesis that will perform, look, and feel like a natural limb is the goal of two Revolutionizing Prosthetics programs funded by the Defense Advanced Research Projects Agency (DARPA). Prosthetics are getting closer to mimicking human function, but the loss of touch is one of the biggest hurdles researchers need to overcome. In a new study, researchers from the University of Chicago have developed a “blueprint” that could surface the way for real-time sensory feedback.

Last week the US defence force announced that it has given a paralysed man the ability to ‘feel’ physical sensations through a prosthetic robotic hand that’s been directly connected to his brain. Having been paralysed for more than a decade due to a spinal cord injury, the man was able to identify when and which of his prosthetic fingers was being gently touched by an object – and all while blindfolded.

The technology points to a future where people with paralysed or missing limbs can not only get back the ability to control objects and move about, but can also learn to sense which it is they’re touching.

The development of a sense of touch in prostheses could be developed in the same way as mind-controlled artificial arms and limbs. The University of Chicago said in a statement that the sense of touch lets humans differentiate between objects and textures while also informing our grip and other parts of our daily routine.

The new research, published in the Proceedings of the National Academy of Sciences, by Sliman Bensmaia could pave the way to add touch to prostheses, making artificial limbs feel like a “natural extension of our bodies.” The blueprint to restore touch was developed by analyzing monkeys and was inspired by previous work developing a direct interface linking the brain to the prosthetic.

Bensmaia is trying to reproduce touch by stimulating the brain to recreate how a human processes sensory information. “To restore sensory motor function of an arm, you not only have to replace the motor signals that the brain sends to the arm to move it around, but you also have to replace the sensory signals that the arm sends back to the brain,” said Besmaia in a statement.

Using monkeys, due to their similar sensory systems, the researchers isolated neural activity that was associated with object manipulation, contact and pressure, successfully recreating that pattern artificially. For contact, the researchers trained the monkeys to respond to physical contact, later attaching electrodes to stimulate parts of the brain associated with individual fingers to recreate contact through artificial means. The monkeys responded to artificial contact in the same way they responded to actual contact. The researchers developed a system to recreate the sensation of pressure, once again successfully stimulating parts of the monkey’s brain to artificially create that sensation while also recreating neural activity associated with first touching, or releasing, an object.

US Defense Advanced Research Projects Agency (DARPA) program manager Justin Sanchez said in a press statement that they have completed the circuit. Prosthetic limbs that can be controlled by thoughts are showing great promise, but without feedback from signals travelling back to the brain it can be difficult to achieve the level of control needed to perform accurate movements. By wiring a sense of touch from a mechanical hand directly into the brain, this work shows the potential for flawless bio-technological restoration of near-natural function.”

DEKA, founded in 1982 by inventor Dean Kamen, focuses on the development of new technologies and innovative solutions. Its main success has been with medical products for companies such as Johnson & Johnson, which contracted with DEKA to develop the Independence IBOT mobility system for handicapped persons. The $18.1 million Revolutionizing Prosthetics 2007 program was awarded to DEKA Research and Development Corp. of Manchester, NH.

The DEKA Arm System – tenderly dubbed ‘Luke’ (as in Luke Skywalker) – was first showcased back in the month of February, when a US army vet used the battery-powered prosthetic to scale a rock-climbing wall, using nothing but his brain power.

Now the team behind the technology has demonstrated how the battery-powered device can impart the feeling of touch on top of grip, movement, and object manipulation. They did this by placing electrode arrays onto a paralysed volunteer’s sensory cortex – a region in the brain that’s responsible for identifying and processing the sense of touch, which is defined by the amount of pressure that something asserts – which connected up to the prosthetic device.

Arrays were also placed on the volunteer’s motor cortex, which is responsible for facilitating body movements. “The wires from the motor cortex allow the wearer to control the motion of the robot arm, and pressure sensors in the arm that connect back into the sensory cortex give the wearer the sensation that they are touching something,” Mike Murphy told Quartz.

Loaded with highly sensitive torque sensors, the device could detect changes in pressure as they are applied to the fingers, and this was converted into electrical signals that were fed into the volunteer’s brain.

When testing the arm in the lab, the researchers gently touched each of the fingers while the volunteer was blindfolded, and he reported with almost 100 percent accuracy which one was being touch, saying that it felt just like his own hand was being touched.

Sanchez said “At one point, instead of pressing one finger, the team decided to press two without telling him.” “He responded in jest asking whether somebody was trying to play a trick on him. That is when we knew that the feelings he was perceiving through the robotic hand were near-natural.”

The experiment was described at the Wait, What? A Future Technology Forum, hosted by DARPA in the US last week. The team is remaining fairly silent on the finer details of the technology right now, as they’re working on getting everything peer reviewed and accepted for publication in a scientific journal.

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