A man paralyzed from the neck down for about 12 years is now able to use a robot arm to shake hands and even play "rock, paper and scissors," all with the help of a brain implant that can read his intentions, scientists reported today.
"I was surprised at how easy it was," the 32-year-old patient Erik G. Sorto said in a statement. "I remember just having this out-of-body experience, and I wanted to just run around and high-five everybody."
The new prosthetic improves on previous attempts at developing mind-controlled robotic limbs that had focused on reading the raw, highly specific movement signals in the brain and resulted in jerky movements. The new approach reads a person's "plan for action" and let the robotic arm execute it.
"It was very exciting to watch this work even for complicated actions," said Richard Andersen, a neuroscientist at the California Institute of Technology in Pasadena. "I think it's an important advance. We're very happy with the way it turned out."
Robotic limbs are nowadays often controlled by electrodes implanted in the brain, aiming to harness the brain signals that are isolated from the body after a spinal injury. Previously, scientists had put microchips in
the motor cortex, a part of the brain that directs voluntary physical activity. However, this led to motions that were delayed and jolting, not the smooth gestures associated with natural movement. This is because the motor cortex controls many different muscles, so for any one gesture, patients had to painstakingly focus on which muscles to activate for each specific component of the gesture. For example, when it comes to picking up a cup of water, one might have to concentrate about lifting one's arm, extending the arm, closing the hand around the cup, and so on.
But in the new experiment, reported in the May 22 issue of Science, Andersen and his colleagues decided to implant the electrodes in a different part of the brain, the posterior parietal cortex, or PPC, which is located on the top of the brain near the back. Research in monkeys and humans has shown that PPC controls the intent to move rather than the details of executing movements. The scientists hoped that this approach would allow the patient to produce more natural, fluid motions.
Image: Erik Sorto making a smoothie with brain control. Credit: Spencer Kellis
In a clinical trial designed to test the safety and effectiveness of the new approach, neurosurgeon Charles Liu at the University of Southern California and his colleagues implanted a pair of NeuroPort electrode arrays in two parts of the PPC of Sorto, who was paralyzed from the neck down due to a gunshot wound.
The arrays were implanted in 2013 and were each only about 4 millimeters by 4 millimeters large. Each array contained 96 electrodes that each recorded the activity of a single neuron in the PPC.
Using functional magnetic resonance imaging (fMRI), the researchers monitored Sorto's neurons while he imagined various kinds of limb and eye movements. Based on the neural activity they recorded, the scientists were able to determine which limbs Sorto wanted to move, as well as where he wanted to move them, when, and how fast. This information was then used to help Sorto intuitively steer a computer cursor or to direct a robotic arm situated beside him to its intended location. The brain's intentions could be decoded in just 190 milliseconds — for comparison, a blink of an eye lasts between 100 to 400 milliseconds.
Image: The surgical team. Credit: Spencer Kellis
Over time, Sorto refined his control of the robot arm, providing researchers were more details about how the PPC works. For example, if Sorto thought that he should move his hand toward an object, intentionally trying to control the robot limb, that did not work. It was much easier if he just thought, "I want to grasp the object."
The scientists hope that by refining the technique, one day quadriplegic patients can carry out more practical tasks and regain some of their independence.
"The project has made a huge difference in my life. It gives me great pleasure to be part of the solution for improving paralyzed patients' lives," Sorto said. "I joke around with the guys that I want to be able to drink my own beer — to be able to take a drink at my own pace, when I want to take a sip out of my beer and to not have to ask somebody to give it to me. I really miss that independence. I think that if it was safe enough, I would really enjoy grooming myself — shaving, brushing my own teeth. That would be fantastic."
The scientists are now working to improve patient dexterity by providing sensory feedback from the robot limbs. "Right now we have three patients with implants in their somatosensory cortex, the part of the brain that controls body sensations, and their robot hands are sensorized, so when the robot hands touch something, it leads to stimulation of the somatosensory cortex to provide the feeling of touch," Andersen said. "The goal is to improve dexterous manipulation. These studies have just started."