You have probably completed countless tasks with your hands without giving them a second thought. But if you wear gloves that dull your sense of touch, even simple actions can become frustrating. Remove proprioception—your ability to sense your body’s position and movement—and you might even drop objects or injure yourself.
A testing participant controls a bionic hand through a brain-computer interface that allows him to feel pressure changes as the steering wheel moves in the hand. Image Credit: Charles Greenspon
A team of researchers have made significant progress in addressing this challenge. Their latest research, published in Nature Biomedical Engineering and Science, explores how precise electrical stimulation of the brain can recreate tactile feedback, allowing prosthetic hands to provide a real sense of touch.
Most people don’t realize how often they rely on touch instead of vision—typing, walking, picking up a flimsy cup of water. If you can’t feel, you have to constantly watch your hand while doing anything, and you still risk spilling, crushing, or dropping objects.
Charles Greenspon, Study Lead Author and Neuroscientist, University of Chicago
The Science of Restoring Sensation
Years of cooperation between scientists and engineers from UChicago, the University of Pittsburgh, Northwestern University, Case Western Reserve University, and Blackrock Neurotech are reflected in these new findings. Together, they are developing, constructing, deploying, and improving robotic prosthetic arms and brain-computer interfaces to help individuals who have lost substantial limb function regain both motor control and feeling.
Neuroscientist Sliman Bensmaia oversaw the research at UChicago until he passed away in 2023.
The researchers’ approach to prosthetic sensation involved placing tiny electrode arrays in the parts of the brain responsible for moving and feeling the hand. On one side, a participant can move a robotic arm by simply thinking about movement, and on the other side, sensors on that robotic limb can trigger pulses of electrical activity in the part of the brain dedicated to touch.
For about a ten years, Greenspon explained, this stimulation of the touch center could only provide a simple sense of contact in different places on the hand.
Greenspon added, “We could evoke the feeling that you were touching something, but it was mostly just an on/off signal, and often it was pretty weak and difficult to tell where on the hand contact occurred.”
The recently released findings represent significant advancements in overcoming these constraints.
Advancing Understanding of Artificial Touch
In the first study, the research team focused on ensuring that electrically evoked touch sensations are stable, accurately localized and strong enough to be useful for everyday tasks.
By applying brief pulses to individual electrodes in participants’ sensory regions and recording their feedback on the location and intensity of each sensation, the researchers created detailed maps linking specific brain areas to corresponding parts of the hand. Their findings showed that stimulating two closely spaced electrodes simultaneously resulted in a clearer and more intense sensation, improving participants’ ability to pinpoint touch location and pressure accurately.
The researchers also conducted extensive tests to confirm that each electrode consistently produced the same sensory response over time.
“If I stimulate an electrode on day one and a participant feels it on their thumb, we can test that same electrode on day 100, day 1,000, even many years later, and they still feel it in roughly the same spot,” Greenspon added.
For any clinical device to be practical, it must offer stable and reliable performance. An electrode that constantly shifts its touch perception or produces inconsistent sensations would require frequent recalibration, making it frustrating to use. In contrast, the long-term stability observed in this study suggests that prosthetic users could develop confidence in their motor control and sense of touch, similar to how they experience natural limb sensation.
Adding Feelings of Movement and Shapes
The team's latest research goes one step further, making artificial touch even more immersive and intuitive. The effort was directed by first author Giacomo Valle, a former Postdoctoral Scholar at UChicago who now conducts bionics research at Chalmers University of Technology in Sweden.
“Two electrodes next to each other in the brain don’t create sensations that ‘tile’ the hand in neat little patches with one-to-one correspondence; instead, the sensory locations overlap,” explained Greenspon, who shared senior authorship of this study with Bensmaia.
The researchers aimed to determine whether they could use the overlapping nature of touch sensations to help users perceive object boundaries or detect motion across their skin. By identifying pairs or clusters of electrodes with overlapping “touch zones,” they activated them in carefully coordinated patterns to create sensations that moved across the sensory map.
Participants reported experiencing a smooth, gliding touch across their fingers, even though the stimulus was delivered in small, discrete steps. The researchers attribute this effect to the brain’s ability to integrate sensory inputs, effectively “filling in” gaps to create a continuous perception of movement.
This method of sequentially activating electrodes also enhanced participants’ ability to recognize complex tactile shapes and respond to variations in the objects they interacted with. In some cases, they could identify letters of the alphabet traced electrically onto their fingertips and use a bionic arm to stabilize a steering wheel when it started to slip.
These findings bring bionic feedback closer to replicating the precision, adaptability, and complexity of natural touch, supporting the development of prosthetic devices that enable confident interaction with everyday objects and dynamic environments.
The Future of Neuroprosthetics
The researchers believe that when electrode designs and surgical methods improve, the coverage across the hand will become even finer, resulting in more lifelike input.
We hope to integrate the results of these two studies into our robotics systems, where we have already shown that even simple stimulation strategies can improve people’s abilities to control robotic arms with their brains.
Robert Gaunt, Associate Professor, University of Pittsburgh
Greenspon underlined that the objective for this work is to improve the freedom and quality of life of people who have lost limbs or are paralyzed.
He further stated, “We all care about the people in our lives who get injured and lose the use of a limb — this research is for them. This is how we restore touch to people. It’s the forefront of restorative neurotechnology, and we’re working to expand the approach to other regions of the brain.”
This approach could also benefit individuals with other forms of sensory loss. The research team has worked alongside surgeons and obstetricians at UChicago on the Bionic Breast Project, an initiative aimed at developing an implantable device to restore touch sensation following a mastectomy.
While challenges remain, these recent studies provide strong evidence that the goal of restoring touch is becoming more attainable. With each discovery, researchers move closer to a future where prosthetic limbs are not only functional tools but also a means of experiencing the world.
Journal References:
Greenspon, C. M., et. al. (2024) Evoking stable and precise tactile sensations via multi-electrode intracortical microstimulation of the somatosensory cortex. Nature Biomedical Engineering. doi.org/10.1038/s41551-024-01299-z
Valle, G., et. al. (2024) Tactile edges and motion via patterned microstimulation of the human somatosensory cortex. Science. doi.org/10.1126/science.adq5978