Mind-controlled robotic prosthetics are marvellous inventions, restoring vital mobility and independence to amputees. But they do have their limitations. One of these is the sense of touch. Without touch, it's hard to gauge temperature, pain and pressure; the latter of which helps us from crushing soft or delicate objects, such as eggs and fruit.
The USA's Defence Advanced Research Projects Agency has helped fill this gap, designing a prosthetic hand that has allowed a 28-year-old man to feel physical sensations. As the result of a spinal cord injury, the man has been paralysed for over a decade, but while wearing the prosthetic hand he was able not just to "feel" when the hand was being touched, but which finger.
The hand operates by being wired directly into the brain's motor cortex region. This allows electrical signals from the brain to be translated into movement by the hand. To develop a sense of touch in the hand, this concept was extrapolated further -- electrode arrays, typically used to measure voltage and current, were implanted into the patient's sensory cortex, the part of the brain responsible for identifying touch sensations.
"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 precise movements. By wiring a sense of touch from a mechanical hand directly into the brain, this work shows the potential for seamless bio-technological restoration of near-natural function."
The electrode arrays in the patient's motor and sensory cortices were connected to a mechanical hand developed by researchers at Johns Hopkins University's Applied Physics Laboratory, fitted with torque sensors that can detect pressure on the fingers. These pressure inputs are then converted into electrical signals and transmitted to the electrode array on the patient's sensory cortex.
The array is similar to a, developed jointly by researchers at Cleveland Veterans Affairs Medical Center and Case Western Reserve University and led by Dustin Tyler. Tyler's hand was able to feel physical sensation through an electrode array that was placed around nerve bundles in the patient's arm. The patient was tasked with removing the stems from cherries. Without the sensation system, he damaged nine out of 15 cherries; with it turned on, he only damaged one cherry.
The DARPA system was tested a little differently. The patient was blindfolded, and researchers gently touched the fingers of the prosthetic hand, one at a time. He was able to report with nearly 100 percent accuracy which finger was being touched, describing the feeling like being touched on a real hand.
"At one point, instead of pressing one finger, the team decided to press two without telling him," Sanchez said. "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 research was presented last week at DARPA's Wait, What? A Future Technology Forum, held in St Louis.