Creating an artificial sense of touch

A participant used a bionic arm controlled by the brain to steer a wheel in response to movement cues (left, right, none) encoded via intracortical microstimulation across multiple fingers. Valle et al., Science

The sense of touch involves a complex network of nerve fibers running from the skin to the brain. If any link in this chain is broken, such as from the loss of a limb, a spinal cord injury, or a stroke, this sense can be disrupted or lost.

Advanced bionic limbs could potentially tap directly into the brain to provide an artificial sense of touch. This would let people control and receive sensory feedback from robotic arms and hands, or even artificial limbs attached to a wheelchair instead of their bodies.

To provide a simulated sense of touch for bionic limbs, researchers have been experimenting with intracortical microstimulation (ICMS) of the brain. This technique involves placing tiny electrodes into an area of the brain called the somatosensory cortex. This brain region processes sensory information from the arms and hands.

When different ICMS electrodes are activated at different times, they have been able to produce rough approximations of the location and intensity of touch sensation. But to date, they haven’t been able to replicate complex experiences such as texture and motion.

In a new study, funded in part by the NIH BRAIN Initiative, a team led by Dr. Giacomo Valle from the University of Chicago and Chalmers University of Technology in Sweden tested a new ICMS system designed to provide a richer sense of touch. The team placed ICMS electrodes into the somatosensory cortex in two participants. Both had spinal cord injuries that disrupted communication between the brain and the hand.

The researchers used recent breakthroughs in understanding the structure and organization of the somatosensory cortex to precisely place the electrodes. They then tested the ability of the electrodes to mimic the electrical signals that represent the sense of touch. Results were published on January 17, 2025, in Science.

When the researchers activated the electrodes in a pattern designed to evoke the sensation of touching an edge, the participants reported feeling edge-like sensations. Other stimulation patterns let participants identify simple shapes that would normally require feedback from several different fingers at the same time. Some patterns mimicking multiple fingers gave participants complex touch sensations, such as grasping a can or holding a pencil or a ball.

This brain activation was fast enough to enable real-time feedback to and from bionic limbs. The electrodes could also evoke the sensation of motion on the skin in four different directions. In a final experiment, one participant was able to use the electrodes to communicate with a stand-alone bionic arm and steer a wheel in response to the sensations of movement provided via the implanted electrodes.

“This work went beyond anything that has been done before in the field of brain-computer interfaces. 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,” Valle says.

More work will be needed before such systems could be tested in larger studies, including the development of smaller and more powerful sensors for bionic limbs.

—by Sharon Reynolds