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Innovations in Imaging

The Magic of Touch

 

Researchers have developed a neural prosthesis system that sparks the sensation of feeling.

 


The neural prosthesis developed in Dustin Tyler's lab is no sleight-of-hand trick.
It allows research participants to not only have motor control, but also feel objects, too.

 

At last year’s D60 symposium celebrating the Defense Advanced Research Projects Agency’s 60th anniversary, attendees got an up-close look at DARPA’s breakthrough technologies. For Brandon Prestwood, one of those technologies is both up-close and personal.

Prestwood lost his left arm below the elbow in an industrial accident in 2012. Three years ago, he became a subject in a study conducted by Dustin Tyler, Kent H. Smith Professor II of Biomedical Engineering at Case Western Reserve University. Tyler has developed a neural prosthesis system to provide sensation and human-in-the-loop control for amputees. 

In the crowded D60 exhibit hall, Prestwood slowly extended his neural prosthesis and grasped the hand of his wife Amy. For the first time since the accident, he felt her touch with his left hand. “I felt the connection you are supposed to have,” says Prestwood. “It was a life-changing moment.”

 

Early Work in Implanted Devices

Creating life-changing moments – and technologies – has been Tyler’s goal since beginning his work in neural engineering as a graduate student at Case Western Reserve University in 1992. “My career has centered around electrode development for connecting to the nervous system, using tools like computational modeling and in vivo biologic studies, to figure out how to build a device to put electrical fields into the nerve to get different activations in the nerve,” says Tyler, director of the Functional Neural Interface Lab, associate director of the Cleveland Advanced Platform for Technology (APT) Center and investigator in the Cleveland Functional Electrical Stimulation (FES) Center.

 


Research participants test the sensory prosthetics in the Functional Neural Interface Lab.

 

After earning his doctorate degree, Tyler worked several years for NeuroControl Corp., a Cleveland company that commercialized neurostimulation technologies first created in labs at Case Western Reserve University. Calling the experience his “second Ph.D.,” Tyler says, “The skills and ideas I picked up in that industrial experience related to actual product design, design control and working with the FDA have been instrumental in enabling and guiding my current work.”

After leaving NeuroControl, Tyler’s initial research as a principal investigator with the Louis Stokes Cleveland Veterans Affairs Medical Center and in his Functional Neural Interface Lab centered around interfacing with the nervous system for functional purposes, such as treating dysphagia following stroke and restoring motor function to patients with upper and lower spinal cord injury. 

Tyler’s work on upper extremities with Robert Kirsch, chair of Case Western Reserve University’s Biomedical Engineering Department, and on lower extremities with Ronald Triolo, biomedical engineering professor and executive director of the APT Center, led to clinical trials and spurred his interest in moving beyond motor function to sensory stimulation.

Tyler began his sensory stimulation work in individuals with limb loss. “The main thing that’s missing for people without a limb, but otherwise able-bodied, is feeling,” says Tyler. “Even with great prosthetic motor control, they can’t feel anything. Many people abandon myoelectric prostheses – the current state-of-the-art for upper limb amputees – because it doesn’t feel like their hand. It’s just a foreign tool to them.”

 

The Addition of a Sensory Interface

With initial funding from the VA Rehabilitation Research and Development Service, Tyler’s lab created its first sensory interface, which was implanted in subjects in 2012. Sensors on the prosthesis record the pressure applied between the hand and objects as the hand closes around them. These sensors are connected to an external system that transforms the pressure signals into a neural code that is transported through wires to electrodes that are surgically implanted in the subjects’ residual arms. When the neural code reaches the nerves, a connection is made between the prosthetic and the brain, which interprets the signals as a sense of feeling in the subject’s own hand.

Prestwood remembers the first time Tyler’s team tested the sensory interface in his prosthetic in the lab. They began gradually, increasing the electrical stimulation little by little until Prestwood felt a tingling in the tip of his index finger. “The first time I felt it, I said, ‘Damn, it worked!’” recalls Prestwood. “I like to think I’m a tough guy, but I got very emotional thinking about how much this would affect me every time I touched something. It was so liberating!”

Tyler says that early tests confirmed the system could provide sensation on locations all around the hand. “We’ve been building on that since,” he says. “When you stimulate a nerve, a message goes back to the brain and there’s all kinds of relay stations and processing that happens before the subject actually perceives what that feels like. It’s a very complex challenge.” Researchers in the Functional Neural Interface Lab were the first group with a permanently implanted sensory interface that’s still going today. “With that, we could do a lot of different studies to begin to understand what perception is and how subjects feel different things,” adds Tyler.

One of the critical changes the group has since made to the sensory system was to move from utilizing a string of square pulses, which had been used for motor function, to modulating the amplitude, pulse width and rate. “There are several different types of sensors in your fingers – rapidly adapting, slowly adapting – and different sensor modalities,” says Tyler. “In normal touch, they fire differently. If you stimulate with steady square pulses for everything, they fire at the same rate. And that’s not normal.”

By modulating the amplitude, pulse width and rate, thereby adding more information into the sensory system, the research team changed the sensory experience for users. Rather than feeling a tingling sensation, similar to when the hand falls asleep, users get a pulsing sensation more akin to normal touch. 

Tyler and his colleagues also began delving deeper into the science of touch to decipher its patterns and dimensionality. It’s no longer just a matter of whether subjects feel their hands, but rather how the brain interprets touch and where the data is processed in the body’s entire sensory system.

 

Connections to the World

About five years ago, Tyler’s lab received additional funding from DARPA’s Hand Proprioception and Touch Interfaces (HAPTIX) Program, which allowed the team to create a more robust system that couples the sensory interface with implanted intermuscular electrodes. The latest system records from 16 muscles and has 64 nerve channels – double the previous system – and uses Bluetooth® wireless technology. “It’s completely implanted, connects to a cell phone and users are connected to their hand,” says Tyler. 

The lab is waiting on approval from the Food and Drug Administration that would allow for implantations in subjects in a randomized clinical trial. Tyler is excited by the possibilities, particularly given the difference the neural prosthetic system has made in the lives of those who first tested the system outside the lab, at home, for five weeks. During the first two weeks, they used the prostheses with motor function alone, then they turned on the sensory stimulation for the third week and finally turned it back off for the last two weeks.

“In all cases, their social interaction, sense of self, wholeness and satisfaction went up significantly during that one week when sensation was on and it went back down when we turned it off again,” says Tyler. Through the years working on this project, he’s slowly learned just how important sensation is.

“What I didn’t fully appreciate when I started – and I do now on many levels – is that the hand is the primary connection to the world,” he says. “It’s equally as much an emotional organ for us as it is a functional organ.”

Prestwood knows that first-hand. He looks forward to having the sensory prosthetic full time so he can fish with his son Jake and hold hands with his niece Katelyn, who he calls “near-and-dear to my heart.” Like Tyler, he has bigger dreams, too.

“When I first started in the study, I thought a lot about how it was going to change my life and my interactions,” says Prestwood. “Soon after I had my sensation restored and some intuitive motor control, I realized it wasn’t about me anymore. It’s about everybody that’s injured. This technology has to get out to everybody.

 

 

 

The Melding of Man and Machine

The German philosopher Immanuel Kant posited that all knowledge is gained through experience and impressions of the senses. Through years of work on neural prosthetic systems that restore the sense of touch to amputees, Dustin Tyler has begun to embrace this philosophy and consider its future implications.

“What neural interfacing brings is a connection to the sensory systems,” says Tyler, Kent H. Smith Professor II of Biomedical Engineering at Case Western Reserve University. “If we can control all the senses and integrate the timing appropriately, there will be no distinction between reality and the neuro-stimulated reality.” Such an idea is admittedly hard to wrap your head around, but consider it a step beyond virtual reality – which primarily taps into sound and sight – to full multisensory synchrony that replicates the world around you.

These metaphysical ideas are the basis behind the Human Fusion Institute being spearheaded by Tyler. He has organized meetings among dozens of multidisciplinary experts interested in furthering the symbiotic relationship between humans and technology. The group is currently building a mission statement and defining the purpose of the Human Fusion Institute, taking into consideration philosophical, ethical, legal and regulatory issues. “Rather than thinking of technology and humans as separate, we think of how we can beneficially fuse them together,” says Tyler.

One scenario where a synergetic connection between humans and technology could be advantageous is in disaster cleanup, such as after a nuclear accident when it’s biologically dangerous for people to be on the ground. “If I can remove you from that physically, but put all your senses there via a synchronized device – your intelligence, creativity and critical thinking – that’s revolutionary,” says Tyler.