Artificial touch for brain-controlled bionic hand

Researchers, who are all part of the U.S.-based Cortical Bionics Research Group, have discovered a method for encoding natural touch sensations of the hand via specific microstimulation patterns in implantable electrodes in the brain. This allows individuals with spinal cord injuries to control a bionic arm with their brain and to feel tactile edges, shapes, curvatures, and movements.

“In this work, for the first time the research went beyond anything 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’re at 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,” says Giacomo Valle, lead author of the study and assistant professor at Chalmers University of Technology.

Importance of the sense of touch

For individuals with a spinal cord injury, electrical signals coming from the hand to the brain – that should allow an individual to feel tactile sensations – are blocked by the injury and that sense of touch is lost. A bionic limb controlled by the user’s brain signals can bring back some functionality and independence to someone with a paralyzed hand, but without the sense of touch, it’s very difficult to lift, hold, and manipulate objects. Previously, a bionic hand wouldn’t be perceived by the user as part of the body, since it wouldn’t provide any sensory feedback. This study aimed to improve the usability of an extracorporeal bionic limb, which would be mounted on a wheelchair or similar equipment close to the user.

Implantable technology

For the study, two BCI participants were fitted with chronic brain implants in the sensory and motor regions of the brain representing the arm and hand. Over the course of several years, the researchers were able to record and decode all the different patterns of electrical activity that occurred in the brain related to motor intention of the arm and hand. This was possible, since electrical activity was still present in the brain, but paralysis was blocking this from reaching the hand. Decoding and deciphering brain signals with this technology is unique and allows the participants to directly control a bionic arm and hand with the brain for interacting with the environment.

Complex touch typed into the brain

The participants were able to accomplish a series of complex experiments requiring rich tactile sensations. To do this, the researchers typed specific stimulations directly into the users’ brains via the implants.

“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,” Valle says.

The participants could feel the edge of an object, as well as the direction of motion along the fingertips.

By using the BCI, the researchers could decode the intention of motion from the participant’s brain in order to control a bionic arm. Since the bionic arm has sensors on it, when an object encounters these sensors, the stimulation is sent to the brain and the participant feels the sensation as if it were in their hand. This means participants could potentially complete complex tasks with a bionic arm with more accuracy than previously possible.

The future of complex touch for neural prosthetics

This research is just the first step toward patients with spinal cord injuries being able to feel this level of complex touch. To capture all the features of complex touch researchers can encode and convey to the user, more complex sensors and robotic technology are needed (for example prosthetic skin). The implantable technology used to stimulate would also require development, to increase the repertoire of sensation.

Chalmers University of Technology
https://www.chalmers.se