Neuroscience seeks sense of touch

Asst. Prof. Sliman Bensmaia's research fuels goal of touch-sensitive prosthetics

Story adapted from the Science Life blog

Sliman Bensmaia didn’t always want to be a neuroscientist. While studying computer engineering and cognitive science as an undergraduate at the University of Virginia, he planned to graduate quickly so he could follow his true calling.

“At the time I wanted to be a musician, so I just wanted to get a degree and get out of there,” he said.

Bensmaia's rock star dreams didn’t pan out, but he found another passion in cognitive psychology. As a graduate student at the University of North Carolina, he worked in a psychology laboratory studying the sense of touch, then joined a prominent somatosensory neurophysiology lab at Johns Hopkins University. He became an expert at the intersection of neuroscience and emerging efforts to control robotic limbs with the brain.

Now an assistant professor in Organismal Biology and Anatomy, Bensmaia studies how the peripheral and central nervous systems represent the world around us. His research has led to groundbreaking insights about how we perceive objects and textures through the sense of touch, and may one day lead to prosthetic devices that completely restore a realistic sense of touch for amputees and tetraplegic patients.

Our ability to grasp and manipulate objects relies on feedback from our sense of touch. Without these signals from the hand, we would have trouble performing even the most basic activities of daily living, like tying our shoes or turning a doorknob. Touch is even critical for emotional communication. We touch the people we care about, and it makes our limbs feel like part of us.

Science has made tremendous advances in technology that taps into signals from the brain to allow patients to move prosthetic limbs, but an important element to creating a realistic replacement for a hand is the sense of touch. Without somatosensory feedback from the fingertips about how hard you’re squeezing something or where it’s positioned relative to the hand, grasping an object is about as accurate as using a mechanical skill crane at an arcade to grab a stuffed animal.

Neural mechanisms behind touch 

Bensmaia’s research has focused on how the nervous system interprets sensory feedback as we touch or pick up objects, move our limbs, and run our fingers along a textured surface. Understanding how the brain interprets this multitude of signals will allow scientists to recreate this crucial sensory feedback through prosthetics equipped with sensors that send electrical signals to electrodes implanted in the brain.

Last October, Bensmaia and his colleagues published a study in the Proceedings of the National Academy of Sciences that provided a blueprint for building such touch-sensitive prosthetics. In a series of experiments with monkeys, whose sensory systems closely resemble those of humans, they identified patterns of neural activity that occur during natural object manipulation and then successfully induced these patterns through artificial means.

The work revealed the neural mechanisms underlying the sensations of contact location—or sensing where the skin has been touched—how much pressure is applied, and when the hand first touches or releases an object. While the paper provided a comprehensive set of instructions for reproducing realistic sensations of touch, Bensmaia said his team’s work is far from finished.

“We’re just opening the door at this point. We have some beginnings of answers, but every time you discover something it raises as many questions as it answers,” he says. “We’re just beginning a journey to restoring touch in all its glory.”

As for his career choices, he said he made the right one, though he moonlights as the keyboardist in a funk band, FuzZz, which performs regularly around Chicago.

“I think I’m a world-class scientist, but I’m not a world-class musician,” he says. “That’s the truth.”