Monkeys taught to play a computer game were able to overcome wrist paralysis with an experimental device that might lead to new treatments for patients with stroke and spinal cord injury, according to an Associated Press report. The monkeys retained use of paralyzed muscles by learning to control the activity of just a single brain cell.

The device monitored the activity of a brain cell and used that as a cue to stimulate wrist muscles electrically. Researchers found it could even use brain cells that normally had nothing to do with wrist movement, says study co-author Chet Moritz, University of Washington in Seattle.

Moritz says a large untapped pool of brain cells may be available for letting paralyzed people do things like grasping a coffee cup or brushing their teeth. Though he stressed the approach is years, if not decades, away from use in people.

Moritz and colleagues at the University of Washington in Seattle report the results in a paper published by the journal Nature.

Lee Miller, a researcher at Northwestern University who has done similar work, says any demonstration of a device using brain signals to make paralyzed limbs move is “an important development.”

Miller used the pattern of activity in about 100 brain cells to predict the kind of wrist movement a monkey wanted to make. Moritz said focusing on the output of an individual brain cell instead may turn out to work better for overcoming paralysis.

The research is an example of functional electrical stimulation, or FES, which involves stimulating muscles by applying electrical current. Partially paralyzed people use FES devices now to let them stand, walk, use their arms and hands, and do other things. But they control those devices by flicking a switch, moving joints, or tensing a muscle – even the muscle that lets them wiggle an ear.

Taylor says using brain signals instead could be a particularly good strategy for people paralyzed from the neck down who have few available muscles they can control.

Scientists tested two pigtail macaque monkeys at different times. Each had a hand placed on a flat surface. The animals learned that by using their wrists to press downward with their palms or upward with the backs of their hands, they could make a computer cursor reach a target on a screen. Then researchers temporarily paralyzed their wrists with an anesthetic.

A probe in the animals’ brains monitored how often a single brain cell was firing electrical signals. Once the wrists were paralyzed, the firing rate was converted into an electrical stimulation that went to the wrist muscles. Different firing rates made the hand press downward or upward, or relax. The monkeys quickly learned to use the brain cells to control their wrist muscles and continue moving the cursor.

In people, more complex movements would require monitoring many brain cells at once to activate multiple muscles, Moritz says. Researchers would rely on the brain to coordinate all these signals to produce a useful motion. That's what the brain does when a person learns to swing a tennis racket effectively, he says.

It's also possible that a single brain cell could stimulate a group of muscles, if its signals are relayed to particular sites in the spinal cord.

To view a recent broadcast about the research, visit part I of this story.