For the first time, researchers are bringing a complex sense of touch closer to reality for individuals living with spinal cord injuries. A study published in Science demonstrates the potential of brain stimulation to create nuanced touch sensations using a bionic limb mounted on a chair or wheelchair.
An illustration showing a paralyzed individual with a spinal cord injury, implanted with intracortical electrodes in the brain. This brain-computer interface (BCI) allows the individual to control a bionic limb that is not attached to the body, directly with thoughts, to reach and grasp a coffee mug. Due to embedded sensors, the bionic hand senses the grasped object as if it were being grasped with the human hand, communicating the touch sensations to the user’s brain via advanced neurostimulation. Image Credit: Chalmers University of Technology
The research, conducted by the US-based Cortical Bionics Research Group, introduces a novel method of encoding natural touch sensations. By delivering specific microstimulation patterns through implantable electrodes in the brain, individuals with spinal cord injuries can not only control a bionic arm using their thoughts but also experience tactile sensations like edges, shapes, and motion—experiences previously unattainable.
In this work, for the first time the research went beyond anything that has been done before in the field of brain-computer interfaces (BCI) – we conveyed tactile sensations related to orientation, curvature, motion and 3D shapes for a participant using a brain-controlled bionic limb. We are in another level of artificial touch now. We think this richness is crucial for achieving the level of dexterity, manipulation, and a highly dimensional tactile experience typical of the human hand.
Giacomo Valle, Study Lead Author and Assistant Professor, Chalmers University of Technology
The Importance of the Sense of Touch
The sense of touch is fundamental to performing everyday tasks independently. For those living with spinal cord injuries, signals from the hand to the brain are disrupted, leading to a loss of tactile sensations. While bionic limbs controlled by brain signals offer functionality, their lack of sensory feedback makes tasks like lifting and manipulating objects challenging. Without touch, a bionic hand often feels like a tool rather than an extension of the body.
This study focuses on improving the usability of extracorporeal bionic limbs—robotic arms mounted near the user on a wheelchair or similar device. The aim is to create a seamless connection between the brain and the bionic limb, enabling both control and sensory feedback.
How the Technology Works
In the study, two participants were equipped with chronic brain implants targeting the sensory and motor regions associated with the arm and hand. Over several years, researchers recorded and decoded the patterns of electrical activity in the brain related to the participants' intentions to move their arm and hand. Although paralysis blocked these signals from reaching the limbs, the brain's electrical activity remained intact.
By decoding and interpreting these signals, the technology enabled participants to directly control a bionic arm and hand using their thoughts, allowing them to interact with their environment in ways previously not possible.
Complex Touch Typed into the Brain
The participants successfully completed a series of intricate experiments requiring rich tactile sensations. To achieve this, researchers delivered specific stimulations directly to the brain through the implants.
Valle added, “We found a way to type these ‘tactile messages’ via microstimulation using the tiny electrodes in the brain and we found a unique way to encode complex sensations. This allowed for more vivid sensory feedback and experience while using a bionic hand.”
The participants could feel the edge of an object and even detect the direction of motion along their fingertips.
Using the Brain-Computer Interface (BCI), the researchers decoded the participants' brain activity to control a bionic arm. When sensors on the arm detected contact with an object, signals were sent back to the brain, creating the sensation of touch as if the object were held in a biological hand. This bidirectional communication enabled participants to perform complex tasks with improved accuracy, such as picking up an object and moving it to another location.
The Future of Complex Touch for Neural Prosthetics
This research marks an important first step toward enabling patients with spinal cord injuries to experience complex touch sensations. However, fully realizing this vision will require further advancements in both sensor and robotic technologies, such as the development of prosthetic skin capable of capturing a wider range of tactile inputs.
Additionally, the implantable technology used for brain stimulation will need to evolve to expand the variety and nuance of sensations it can convey. These advancements will be crucial for bridging the gap between current capabilities and the rich, multidimensional tactile feedback of a natural human hand.
Journal Reference:
Valle, G., et. al. (2025) Tactile edges and motion via patterned microstimulation of the human somatosensory cortex. Science. doi.org/10.1126/science.adq5978