Restoring Touch for Amputees Could Spur Greater Human-Machine Fusions
Dustin Tyler‘s research on the neural interface between man and machine plays an integral part in the upcoming ReHAB trial and push toward the Avatar XPrize.
Dustin Tyler may be a tad overly critical when reflecting on his early days as a researcher at Case Western Reserve University. “I was a dumb engineer,” says Tyler, investigator with the Cleveland FES Center, director of the Human Fusions Initiative and Kent H Smith professor in the department of Biomedical Engineering at Case Western Reserve and associate director of engineering & quality of the Veterans Affairs Advanced Platform Technology Center.
That’s not to disparage biomedical engineers or even to lessen the importance of his work to restore upper and lower extremity function for amputee, stroke and spinal cord patients. Mostly, the comment reflects Tyler’s evolution as a scientist and thinker who has spent more than two decades researching the neural interface between man and machine.
“The beautiful thing about working with people over the long term is you get to know them and know what matters,” he says.
Initially, Tyler expected amputee subjects to want a prosthetic hand that looked good and functioned at a high level. But while those considerations were important, that’s not what people wanted most. “Every single one of them said, ‘I want to hold my wife’s hand’ or ‘I want to feel my kid,’” he says. “What it comes down to is connecting.”
Channel Finder: Implanted in 2012, Tyler’s first sensory interface combines prosthetic sensors with an external system that translates pressure into neural code. These impulses are transmitted back into the nervous system via electrodes implanted in nerves in the affected limb. With 10,000 individual axons packed into a single nerve just a few millimeters in diameter, tapping into the proper channels can be challenging. To make that happen, Tyler has been developing a specialized nerve cuff electrode, which flattens the nerve without damaging it. The additional surface area around the nerve creates more potential for contacts to interact with the neurons. “What we’re trying to do is maximize that interface,” says Tyler. “It gives you an amazing appreciation for what the body actually is.”
Cherry Picking: In his early work, Tyler investigated the sensor’s ability to regulate pressure applied by the prosthetic hand. The task involved plucking stems from cherries — an activity that requires a refined ability to grasp. Grip too hard and the fruit breaks, too soft and the stem won’t come off. Without sensation in the prosthetic, subjects broke about half of the cherries. But with it, they could perform the task blindfolded without breaking any. “It has a huge functional impact,” he says.
ReHAB Center: In the coming months, Tyler’s nerve cuff electrodes are expected to be incorporated in a feasibility study of the Reconnecting the Hand and Arm to the Brain (ReHAB) System. Building on six years of work, the ReHAB system uses micro-arrays implanted in the brain’s motor and sensory cortex. The brain activity is connected via computer-brain interface to Tyler’s electrodes in the subject’s arm, which provide activation for movement and return sensory stimulation to the brain. By coordinating the neural activity in the arm and hand with what’s happening in the brain, researchers hope to return function and a sense of feeling to spinal cord patients, stroke victims and others. “Ultimately the beauty of the human body is that it’s always trying to fix itself,” Tyler says. “The goal is to re-establish connections that may not happen naturally. Anything the nerve does, we can try to tap into.”
All the Feels: In September 2018, Tyler’s work was highlighted at a symposium celebrating the Defense Advanced Research Projects Agency’s 60th anniversary. It was a huge honor to be recognized alongside other DARPA-funded advances such as the internet. Yet Tyler relishes a more private moment. The research subject he’d brought to demonstrate the prosthetic hand was in the exhibit hall when his wife saw him wearing it for the first time. Their eyes met, and the man reached for his wife. “She touched his hand,” Tyler says. “All I remember are his words, ‘I feel you. I. Feel. You.’ That was a huge thing.”
Buzz Words: Researchers are still learning the “language” of nerve activation. So participants frequently describe the sensation of touch as a buzzing or a tingling. Tyler has shown more complex stimulation provides more “natural” sensation and believes that advances will eventually make the neural stimulation just like their hand. His research, however, also shows that the stimulation feels more natural as participants learn the new language of sensation. “The brain is plastic. It learns,” he says. “That is the new version of what their hand is. What they feel becomes natural, because they learn it.”
Prize Patrol: Tyler’s current interests lie in what he calls “human fusions,” or a person’s symbiotic relationship with technology. His Human Fusions Institute at Case Western Reserve is among 77 semifinalists for a share of the $10 million Avatar XPrize. The global competition seeks to develop an “Avatar System that will transport a human’s sense, actions and presence to a remote location in real time, leading to a more connected world,” according to its website. For Tyler, it raises the most fundamental of questions about being human. He draws on the ideas of German philosopher Immanuel Kant, who theorized that all our knowledge begins with our senses. “Everything I am — my entire existence — is really the aggregation of all the sensory input I’ve had over time,” says Tyler.
Out of Body Experience: Tyler doesn’t see much difference between his research with prosthetics and an avatar or human-controlled robot exploring the ocean floor. It’s possible to integrate visual and sensory feedback via neurostimulation. So, when the operator moves their arm, it controls the robotic arm and the operator feels what the robot grabs and touches. “If we can take sensory integration from anywhere in the world and give it to you appropriately, then that other place in the world essentially becomes your new location, in many ways,” he argues.
All for One: Since humans’ earliest days, we’ve created tools to improve our lives, but our interaction with that technology has never really changed, Tyler argues. “We hold it, we swing it, we look at it,” he says. While technology plays a huge part in our daily lives, it remains something separate. But those lines are rapidly blurring, which raises tough ethical questions. “Right now, we see this separation between us and the technology,” he says. “We feel in control of it. If I start to integrate it with you in this symbiotic relationship, that changes the equation. People feel very differently about that, because it’s part of you.”