Users of a bionic hand were able to “feel” sensation in such detail that they could blindly identify a letter of the alphabet by tracing it with a fingertip, and users of a bionic arm could control a steering wheel, in two recent studies led by UChicago scientists. The results represent a significant breakthrough in the development of neuroprosthetics.
“I distinctly remember one of the participants, the first time he felt something, started crying. It was a sweet moment,” UChicago neuroscientist and research assistant professor Charles Greenspon said in an interview with the Maroon. “In some cases, these are people who haven’t felt their hands in years until we implanted them.”
According to Greenspon, the findings of the recently published studies will benefit amputees, people with spinal cord injuries, and other patient populations with sensory loss, including women who have had mastectomies. In the coming months, Greenspon and fellow researchers plan to implant electrodes in the participants of the Bionic Breast Project, a collaboration with surgeons and obstetricians at UChicago that aims to produce a device which can restore the sense of touch after a mastectomy.
Greenspon described his research as the “brainchild” of two groups.
“There are clinicians who want to help people rehabilitate and have the maximum quality of life after some kind of injury, and neuroscientists, like myself, who want to understand how touch works and apply that information in meaningful ways,” he said.
Many prosthetic limbs don’t provide sensory feedback to their users, making daily tasks, such as lifting a cup or typing, difficult. Without tactile feedback, a prosthetic hand functions more like a grabber tool.
“If you’ve ever gone to the dentist and had your mouth numbed, you will be very acutely aware of how important the sense of touch is to speaking and moving your mouth—your hand is no different,” Greenspon said.
Ten years ago, the research team first obtained approval from the Food and Drug Administration (FDA) to implant devices in the brain. What followed was years of collaboration between scientists and engineers at UChicago, the University of Pittsburgh, Northwestern University, Case Western Reserve University, and Blackrock Neurotech.
In the first study published in December in Nature Biomedical Engineering, researchers created detailed “maps” of brain areas corresponding to different parts of the hand. They focused on ensuring that stimulating a group of electrodes placed in the brain would reliably trigger the same sensation in the same spot in the hand each time, allowing prosthetic users to develop confidence in their motor control, as they would in their natural limbs.
Greenspon took the lead on the project after UChicago neuroscientist and professor Sliman Bensmaia passed away unexpectedly in 2023.
The software is novel, but the physical hardware of the prosthetics already existed.
“The technology that is currently implanted [in study participants] was developed 30 years ago, but what you can do with the technology grows as you learn more about the brain,” Greenspon said.
Before he passed, Bensmaia and his team laid the groundwork for the recent advances by generating algorithms for brain-computer interfaces, which allow a person to control a device using brain signals. The model mimics the biological processes underlying how the nervous system communicates signals from the arms and hands to create natural touch sensations.
Giacomo Valle, a former postdoctoral fellow at UChicago who is now continuing his bionics research at Chalmers University of Technology in Sweden, is the first author of the complementary paper published today in Science. It uses the results of the first study to further refine sensation by focusing on the building blocks of real-life touch, including identifying the edges and boundaries of objects, as well as their textures.
The brain can stitch together multiple sensory inputs, a feature that the researchers exploited to develop the neuroprosthetics. They first placed clusters of electrodes in the brain corresponding to overlapping touch zones in the hand and arm. Scientists activated these zones by delivering tiny pulses in small, discrete steps, which the brain can interpret as continuous: a gentle gliding touch passing over the fingers, for example.
“It’s not an unexpected phenomenon. If you play three frames of a video really quickly, it just looks like moving. That’s how your brain works,” Greenspon said.
The same is true of touch. “If I have these two things that are a little bit apart, your brain goes, ‘eh, it’s probably one thing,’” he continued.
Neurotech companies such as Precision Biosciences, Paradromics, and Elon Musk’s Neuralink are working to commercialize the technology, according to Greenspon, who said that one of his roles as a researcher is “to build the understanding of the brain such that these companies can do more with their devices.”
Their next challenge is to enable users to handle objects and complete tasks without watching their hands, made possible by proprioception, or the ability to perceive the position of one’s body. “At the moment, what we are able to do relatively well is restore the sense of touch. One of the main goals for a lot of groups over the next 10 or 20 years is to restore proprioception,” Greenspon said.