Reversing the Irreversible – Neuromotor Prostheses for Spinal Cord Injury

A young football player is running the ball downfield when he gets blindsided by two tacklers. They upend the player, who haplessly inverts in the air and lands on his neck. In an instant, his whole body goes limp, and the player has difficulty breathing. Paramedics are rushed to the field, and the player is speedily taken to the hospital, where a CT scan delivers the unthinkable news: complete spinal cord injury.

The player is stabilized medically, and a team of neurosurgeons are brought onto the case. They attach electrodes to the boy’s head, and begin mapping brain activity as they have him imagine using his limbs to carry out a series of specific tasks. Over time, these electrical signals are inputted into a computer, and the computer makes predictions of muscle firing patterns based on the brain activity it receives. The player is brought into the operating room, and numerous fiber optic wires are tunneled under his skin and embedded into muscles in his arms and neck. These wires feed into a pacemaker sized computing device, which receives information wirelessly from electrodes that are implanted on the motor cortex of the player’s brain. The electrodes are tiny wafers, and draw their power off of the electrical activity of the brain itself.

When the player awakens from surgery, he begins a rigorous course of rehabilitation. Through retraining and refocusing his attention, the player is able to move his arms and neck. As both the player and the computing device get smarter, the actions become steadily more natural. In time the player is able to wield subconscious control of his limbs, and propel himself in a wheelchair. The process then repeats all over again for the lower extremities, and eventually the player is able to walk with only the occasional use of a cane.

While this story is far-fetched by today’s standards, the future is yet to be written. The concept of neuromotor prostheses (NMP) is being actively researched in the neuroscience community. An 2006 article in Nature showed the initial first steps being taken towards realizing this goal, and again in 2008 further progress was reported. Currently scientists have been able to temporarily chemically paralyze the wrists of monkeys, and using electrodes attached to computers, reroute brain signals to external wires attached to the wrist muscles. The monkeys were easily able to adapt to the bypass arrangement and begin using their paralyzed wrists to play a video game. Full realization of a functional neuromotor prosthesis is 1-2 decades away from development, but the future of spinal cord injury certainly looks bright.

Reference

Leigh R. Hochberg, Mijail D. Serruya, Gerhard M. Friehs, Jon A. Mukand, Maryam Saleh, Abraham H. Caplan, Almut Branner, David Chen, Richard D. Penn, John P. Donoghue (2006). Neuronal ensemble control of prosthetic devices by a human with tetraplegia Nature, 442 (7099), 164-171 DOI: 10.1038/nature04970

Chet T. Moritz, Steve I. Perlmutter, Eberhard E. Fetz (2008). Direct control of paralysed muscles by cortical neurons Nature DOI: 10.1038/nature07418