Aided by external wires that rerouted signals from their brains, two monkeys regained control of their paralyzed wrists and played a simple video game, scientists said Wednesday.
The study, published in the journal Nature, could one day lead to devices that allow people to regain some control of their limbs after suffering spinal cord injuries and other forms of paralysis, scientists said.
The research is part of a growing field in which scientists are harnessing the power of the brain to overcome paralysis. In a previous experiment, for example, scientists have demonstrated that people who have lost use of their limbs can control a cursor on a computer screen using only their thoughts.
In the latest research, scientists first trained monkeys to make a cursor reach targets on a computer screen by moving their wrists up or down.
Beneath the monkeys' skulls, scientists had implanted electrodes into an area of the motor cortex responsible for hand and wrist movements. As the monkeys played the game, the electrodes recorded signals from individual brain cells so scientists could determine a firing rate.
Once the monkeys had learned the game, scientists implanted wires that ran from the electrodes into the muscles of each monkeys' forearm. Researchers used an anesthetic to temporarily immobilize the animals' wrists.
A small battery-operated device used the firing rate to convert brain signals into electrical stimulation to the monkeys' muscles. Thus, the animals continued to play the target practice game using their otherwise paralyzed wrists to move the cursors.
The monkeys' gaming skills improved with practice, researchers said, peaking at an average of nearly 15 correct hits per minute compared to an average of fewer than five hits per minute at the outset. Game playing sessions were limited by the duration of the anesthetic.
Researchers said they learned that only a single neuron was needed to control a pair of muscles, such as wrist flexors and extensors, and that cells in the motor cortex were capable of stimulating activity.
"Remarkably, every neuron we tested in the brain could be used," said Chet T. Moritz, a researcher at the University of Washington and an author.
The discovery that neurons can be trained to perform new tasks greatly expands the number of cells that the experimental devices may tap into, Moritz said.
