A monkey controlling the hand of its unconscious cage-mate with its thoughts may sound like animal voodoo, but it is a step towards returning movement to people with spinal cord injuries.
The hope is that people who are paralyzed could have electrodes implanted in their brains that pick up their intended movements. These electrical signals could then be sent to a prosthetic limb, or directly to the person’s paralyzed muscles, bypassing the injury in their spinal cord.
Ziv Williams at Harvard Medical School in Boston wanted to see if sending these signals to nerves in the spinal cord would also work, as this might ultimately give a greater range of movement from each electrode.
His team placed electrodes in a monkey’s brain, connecting them via a computer to wires going into the spinal cord of an anaesthetised, unconscious monkey. The unconscious monkey’s limbs served as the equivalent of paralyzed limbs. A hand of the unconscious monkey was strapped to a joystick, controlling a cursor that the other monkey could see on a screen.
From brain to spine
Williams’s team had previously had the conscious monkey practice the joystick task for itself and had recorded its brain activity to work out which signals corresponded to moving the joystick back and forth. Through trial and error, they deduced which nerves to stimulate in the spinal cord of the anaesthetised monkey to produce similar movements in that monkey’s hand.
When both parts were fed to the computer, the conscious monkey was able to move the “paralyzed” monkey’s hand to make the cursor hit a target.
The work demonstrates that it is possible to create movement in a paralyzed limb without directly stimulating the muscles. The next step, says Williams, is to achieve more complex movements, instead of just moving a joystick in two dimensions. “We are hoping to move the arm in many directions,” he says. “To be functionally useful, you have to have fine movements in three-dimensional space.”
Theoretically, the team could have shown the same result using a single monkey and severing its spinal cord but the resulting injury may have obscured the results – and using two monkeys and anaesthesia was more humane.
“It’s the first demonstration of brain-to-spinal-cord information transmission between two animals,” says Rajesh Rao at the University of Washington in Seattle.