Robert Rennaker didn’t follow a traditional path to becoming a world-class engineering researcher. Raised in Topeka, Kansas, and moving regularly from city to city across the Midwest because of the demands of his father’s work, Rennaker wasn’t what you’d call “committed” to high school. In his senior year, he decided to join the military, signed up with the Marine Corps, and shipped off to boot camp in San Diego.
After surviving what he calls the toughest 12 weeks of his life, he was assigned in 1989 to repair the hydraulic and pneumatic systems on the CH-46 Sea Knight, a tandem rotor helicopter used to transport soldiers or deliver food and medicine. Rennaker relished his work. When something goes seriously wrong with a helicopter, there’s no glide path to a soft landing. So when you are on the line to repair one of their critical systems, you better get it right the first time. Rennaker’s attention to detail made him among the best at what he did, so the Marines sent him off to work in the thick dust of Desert Storm, where keeping any complex machine functioning required a minor miracle.
While on leave, he visited his parents’ new home in Phoenix. The neighbors were throwing a party for their daughter, who’d just graduated from college with a degree in aerospace engineering. That’s where Rennaker met Paula Hainsworth, the new graduate. He thought she was smart, confident, and beautiful. That night, he told Paula he was going to marry her. She told him he was crazy, that she was moving across the country for a job in Florida. “I am a Marine,” he told her, “and I make things happen.” During the next 12 months, he put 50,000 miles on his car driving from Jacksonville, North Carolina, to Orlando on the weekends.
After Rennaker’s last deployment, to Yugoslavia, he was honorably discharged, having amassed an impressive collection of 11 medals, including the Humanitarian Service Medal and the Navy and Marine Corps Achievement Medal. He returned stateside and made good on his promise to Paula. The Rennakers now have three children.
But before he became a father, Rennaker still had to figure out what to do with his life. Late one night he was watching a show on the Discovery Channel called The Operation. Each episode follows a patient through an innovative surgical procedure. It hit him. Just like it had when he met Paula. His life’s work would be helping soldiers with neurological injuries by using the technical skills he’d developed in the Marines.
He moved from the University of Central Florida to a highly recognized program at Arizona State University to study biochemical engineering. He loved it so much that he stayed on for both his master’s and doctoral degrees, eventually joining the faculty at the University of Oklahoma. But in Oklahoma he found the entrepreneurial community lacking, so when given the chance in 2009, he jumped at the opportunity to expand his work at the University of Texas at Dallas, where today he manages a series of labs occupying nearly an entire floor of a building; an astounding 100 undergraduate and graduate students are working on his projects. Rennaker also consults with companies he has helped to start or grow.
Which brings us to the groundbreaking work he’s doing with the brain. His service in the Marines gave him the inspiration for it.
“What I bring to the table is an assessment of what needs to be done to help people,” he says. “As a former Marine, I am acutely aware of our veterans and the price they have paid.”
Having worked around helicopters and other loud machinery for many years, Rennaker knew that one malady afflicting many veterans was tinnitus, an incessant ringing in the ears that can cause anxiety, irritability, depression, and even pain. In the worst cases, it leads to suicide. The American Tinnitus Association says that roughly 20 million people suffer from chronic tinnitus. The economic impact has been estimated to be $26 billion a year. The ATA reports that 972,000 veterans have tinnitus linked to their time in the military, meaning they receive disability payments.
When Rennaker started on the problem, there was no effective treatment for tinnitus. The prevailing theory was that the ringing could only be masked by machine-made background noise. There seemed to be no hope of shutting it off. Rennaker wasn’t satisfied with that prognosis. Rather than focus on the ear itself, he started thinking about the circuitry in the brain, specifically how certain stimuli affect how people learn.
In Rennaker’s explanation: “We are walking in the woods and smell a particular odor. If a bear immediately jumps out, and we happen to survive, we will forever connect that smell with the danger of a bear.” If we smell that odor again, we know a bear is nearby and it’s time to bolt. This is called single-trial learning. We don’t need to repeat the bear experience to reinforce the learning. It’s life or death. The lesson sinks in the first time.
Rennaker wondered if this kind of learning could be used to turn off the ringing caused by tinnitus or help with other neurological disorders, such as stroke victims trying to regain fine motor control. Learning to lift a coffee mug after a stroke can be an arduous process, in part because the stakes are so low. But what if lifting the mug could be taught in a situation that created robust neural connections like the kind generated during single-trial learning? The trick was figuring out how to do it without using a bear. Enter the vagus nerve.
The vagus nerve is part of the system that regulates the body’s unconscious actions. Called the autonomic nervous system, it controls, among other functions, heart rate, respiration, and digestion. It also controls our fight-or-flight reflexes. The vagus nerve itself leads from our internal organs to regions of the brain called the locus coeruleus and the nucleus basalis. When stimulated by the vagus, these two special regions signal other parts of the brain by producing powerful chemical stimulants, effectively rewiring the brain. So unlike a computer whose circuits are fixed from the manufacturing stage, the brain can, in theory, rapidly rewire itself if the vagus nerve is stimulated at the right time. This relatively new treatment approach is called vagus nerve stimulation, or VNS, and has been tried on a number of disorders. Rennaker wanted to try it on tinnitus.
Rennaker has invented something he calls the Firefly. It’s a tiny device, about twice the size of a pencil eraser. A surgeon implants it in the neck, where it can be used to electrically stimulate the vagus nerve. Other researchers are trying the same technique, but the Firefly is much smaller than other devices and about a tenth of the cost, meaning it would be available to nearly
Here’s how it works on tinnitus: a set of active nerves creates the ringing in the brain, usually a single tone. VNS training entails playing different but similar tones while the Firefly stimulates the nerve, so that the brain circuitry that processes the alternate tones becomes better connected—in a way, louder—than the circuitry that is misfiring from tinnitus. The net effect is to reduce the overall sound of the tinnitus tone.
Human trials have shown remarkable results, reducing the perception of tinnitus by 24 decibels. As Rennaker puts it, “This is the difference between your vacuum cleaner being on and off while trying to talk.”
With a solution to tinnitus in human trials, Rennaker’s team began to focus on neuroscience’s big-ticket item: strokes. According to the Internet Stroke Center, “Each year approximately 795,000 people suffer from a stroke, with 600,000 of these being first attacks.” Along with other scientists and engineers, Rennaker recognized that VNS could have a major impact on improving the limited movement that comes with a stroke. In theory, VNS with the Firefly was an ideal candidate for mitigating the effects of a stroke and restoring some movement to patients by activating circuits in the brain that have been dormant. Rennaker and his team have been testing this theory on rats. The results there have also
“The most important result in rats to date is that rats with a bilateral spinal cord injury on average recovered twice the amount of strength, compared to subjects with rehabilitation alone,” Rennaker says.
His colleagues in Minneapolis have tried VNS in a small clinical trial with humans. As is typical with stroke victims, they find it frustrating doing even the simplest of things. But VNS has made a major difference. With one female patient, physical therapist Dr. Teresa Kimberley told a local TV station, “I have never seen someone at her state of recovery make as big of gains as she has.” The patient’s husband put it more plainly: “In reality, I got my girl back. I haven’t seen that. It is just a miracle.”
Rennaker has ideas about making North Texas the world center for bioelectronic medicine for the brain. He and his colleagues are gaining national attention for their work. But in the meantime, there are other opportunities to use VNS. The Firefly could potentially work on healthy people, too, in refining critical motor skills. Imagine a professional golfer or baseball player using the Firefly to improve his swing.
“When we give our talks, people think this is magic,” Rennaker says. “But this is not. This is well-understood science.”