The BCI system restores paralyzed man his sense of touch with haptic feedback

BCIs are a booming R&D field, with startups like Elon Musk’s Neuralink looking into a world where humans will connect directly to their computers with external devices (similar in function to an EEG) or biologically implanted BCIs. Such systems require a way to record neural activity (electrode sensors), a way to transmit those signals (like a small set of wireless chips), and algorithms that can translate those signals into action. BCIs are already a medical reality for patients with spinal cord injuries, such as Burkhart, or those suffering from Parkinson’s or epileptic seizures. The benefits that patients obtain far outweigh the risks of surgical implantation.

For the past 90 years, Battelle has been instrumental in developing such outstanding technologies as the Xerox machine, cruise control, and CD-ROMs, along with numerous medical devices. Patrick Ganzer, lead author of the new Cell article, is a research scientist in the organization’s medical devices division, working with the NeuroLife group to develop a BCI for a clinical trial. Burkhart has been working with Ganzer and NeuroLife since 2014 to restore motor function in his right arm.

Battelle’s “neural shunt system” has three main components, according to Ganzer. The first is the surgically implanted chip, placed in an area of ​​the brain that responds to thoughts of movement. The system must then take the brain waves and brain signal recordings and decode what movements the patient is thinking about (in this case, Burkhart). “If I want to open my hand or close my hand, those look like different patterns of activity in the brain,” Ganzer told Ars. Finally, the system translates thoughts into stimulations of the arm muscles, resulting in movement.

While the system has worked well in terms of restoring a wide range of grips and minor functions to Burkhart’s paralyzed hand, his injury is so severe that he has almost no feeling in the hand. “We know how important the sense of touch is for proper control of movement,” Ganzer said. “Even a small change in the ability to feel touch can have a major impact on movement control and overall upper limb function.” So if Burkhart is blindfolded, he can’t detect touch while holding small objects like a pencil, and for larger objects like a Styrofoam cup or glass, his guesses are no better than chance. He has also struggled with simple multitasking tasks, such as drinking a soda while watching television, since controlling your hand with the BCI requires a lot of concentration.

That lack of sensation also means Burkhart isn’t receiving crucial sensory feedback, so “he doesn’t feel like he’s got his own hand,” Ganzer said. It is the reverse of the popular rubber hand illusion, in which sensory feedback from the simultaneous strokes of the real and rubber hands essentially “pairs” the subject with the rubber hand, so that the brain perceives it as an extension of the physical body. “What is known as the body transfer illusion.” The lack of feedback in Burkhart’s case means that there is no critical coupling.

Despite the paralysis, Ganzer and his team found that when they stimulated your skin, neural signals still reached your brain – a phenomenon known as subperceptual brain activity – they were too weak for the brain to perceive. That means Burkhart still has some working nerve fibers in his arm.

So Battelle’s team set out to figure out how to amplify that little signal with haptic feedback, like vibrations from a mobile phone or game controller. Your system uses electrodes on your skin connected to cables that bypass the spinal cord and send those subperceptual tactile signals to and from the BCI implanted in your motor cortex. A band of vibratory motors on the upper arm of Burkhart provides sensory haptic feedback.

The NeuroLife group kept haptic feedback relatively simple to establish a proof of principle, since more complex sensory feedback requires a level of cognitive multitasking that can cause the natural feedback loop to fall apart. But the initial results were extremely promising, particularly for Burkhart’s ability to detect an object blindfolded, relying only on touch. “Ian operates at a random level without this active tactile restoration system,” said Ganzer. “If you activate the system and allow subperceptual touch to increase to conscious perception, your sense of object detection and touch almost reaches 100 percent. This shows that you can increase a subperceptual signal in real time.”

Haptic feedback gives Burkhart more control over his hand movements, as well as the ability to feel the correct amount of pressure to use when lifting different objects, such as a Styrofoam cup, which requires a lighter grip than a heavier ceramic coffee mug. This is also the first BCI that can manage restoration of movement and sense of touch at the same time.

“Instead of his will controlling the grip of the hand, and his movement being thought for many seconds, which can be exhausting, we had residual tactile signals from the brain that were working their way past the spinal cord injury to control the magnitude of this grip. ” Ganzer said. “This allows you to look away from your hands, not having to think about movement, to be able to multitask.” The stimulation cuffs are cumbersome to put on and take off and are also a bit messy, as the electrode links need to stick to the skin. So the researchers also developed a more aesthetically pleasing fabric cover, which is now being tested in clinical studies.

Finally, the team would like to build a version of the system that works just as well at home as it does in the lab and can be controlled by a tablet rather than a desktop computer. According to Ganzer, they have successfully miniaturized the required electronic components to an order of magnitude, making it now portable (about the size of a VHS tape) and mountable in a wheelchair. Burkhart has already been able to use the system as part of his daily routine at home.

Ganzer and his team hope that other people with spinal cord injuries can also benefit from their system, especially since Burkhart’s injury is so severe. “This subperceptual tactile signal is present in many patients,” he said. “Others are likely to have a less serious injury and therefore more reserve nerve fiber tissue.”

DOI: Cell2020. 10.1016 / j.cell.2020.03.054 (About DOIs).