Signals from the brain of one monkey have been copied and transmitted to a paralyzed “avatar” of the same species, causing it to move. The achievement has been claimed as a large step towards allowing people with spinal cord injuries to regain control of their limbs.
Recently there has been rapid progress towards the goal of allowing the brain to connect with the artificial limbs. While this would benefit amputees, a related challenge is to bypass damage to the central nervous system to allow the brain of people with paralysis to reconnect with their own limbs.
“The problem here is not only that of decoding the recorded neural activity into the intended movement, but also that of properly stimulating the spinal cord to move the paralyzed limb according to the decoded movement,” says Cornell electrical engineer Dr Maryam Shanechi.
In Nature Communications Shanechi announced the implantation of a brain chip that could monitor 100 neurons in the master monkey. The avatar was sedated, rather than permanently paralysed, and 36 electrodes planted in its spinal cord.
The master monkey was trained to operate a joystick to catch an onscreen target. The joystick was then given to the sedated avatar while the master was shown the familiar visual stimulus. The master was able, with almost perfect success, to control a cursor operated via a joystick held by the avatar. Where other teams have worried about how the limb needs to move, Shanechi and her colleagues concentrated on the ultimate goal, moving the object being operated.
“By focusing on the target end point of movement as opposed to its detailed kinematics, we could reduce the complexity of solving for the appropriate spinal stimulation parameters, which helped us achieve this 2-D movement,” said co-author Associate Professor Ziv Williams of Harvard Medical School.
Different animals were used in order to prove the signals were not being transmitted by some alternative pathway.
So far the movements achieved have been simple two dimensional shifts, rather than the complex motions of everyday life. The researchers admit their work is a long way from providing natural movement for a paralyzed individual. Even should such technology become available, the muscles of those with longstanding injuries will often have atrophied or become more rigid, making them respond more erratically to renewed brain messages.