Paralysed from neck down after suffering a bullet wound that caused a lesion in his spinal cord more than a decade ago, 34-year-old Erik G. Sorto is today able to move his arm and even serve himself a drink just by thinking about it. Thanks to a collaboration between Caltech, Keck Medicine of University of South California and Roncho Los Amigos National Rehabilitation Centre, U.S., Sorto is the first person in the world to have a neural prosthetic device implanted in the posterior parietal cortex (PPC) which can help him move his arm by imagining the movement.
There have been earlier attempts to have neural implants that would decode the brain’s impulses and help in moving prosthetic limbs, but these have yielded jerky movements unlike smooth natural movements that we are used to. For the first time, the researchers implanted sensory devices in the PPC, which is a region that processes the intention of moving the desired limb, rather than the motor cortex which actually processes the movement itself, as others had attempted to do earlier.
From animal studies, the group led by Richard Andersen of Caltech had identified that the PPC is the region where the intent for making a movement is processed.
The device, a 96-channel electrode array, was implanted in Sorto’s brain in 2013 in the regions of the PPC that control two actions — reach and grasp. Recordings were observed for 21 months and no adverse effects were detected.
For about two years, he trained himself on how to move a robotic arm and a cursor on a computer. He had to imagine a movement of the arm to the desired position and thereby learn to control the movement. With all that effort, today, he is able to perform some tasks with his robotic arm by thinking about them.
Though the procedure and device are not yet ready for commercial use, the research, published recently in Science , represents a huge leap in brain-machine interfaces, especially in its demonstration of the role of the PPC. Especially, it holds promise for individuals who have suffered paralysis due to various causes.