MONKEYS have learned to move their paralyzed limbs by sending the message through wires that connect directly from brain to the target muscles, bypassing the injured nerves.

Similar wiring systems could one day be used to help paralyzed humans regain control of their own bodies.

The study appeared in this week?s issue of the journal Nature.

Better control

Led by Eberhard Fetz, a professor of physiology and biophysics, researchers from the University of Washington worked with two macaque monkeys. They implanted a small electrode array in the monkeys? heads and then temporarily placed a nerve block on the monkeys? upper arms, temporarily paralyzing them. Tiny wires were then run from the animals? heads to their wrist muscles.

Fetz and his colleagues reported that the monkeys learned to control the electric signals sent by the brain to the wrist within minutes of the first practice session. The monkeys were able to make their wrist muscles tense and relax with a thought, even though they couldn?t move their arms.

The method of directly connecting one brain cell to one muscle cell could give patients better control over paralyzed or prosthetic limbs and reduce the adjustment period as well, the researchers said.

For the first time, scientists were able to show that directly linking a brain cell to a particular muscle?instead of linking a cluster of brain cells to a group of wires?could restore one?s control over movements, an ability lost when the spinal cord is damaged.

Power of the mind

Previous experiments de-monstrating the power of the mind have shades of the work done by Fetz and his colleagues.

Back in May, for example, researchers from the University of Pittsburgh showed that monkeys could control prosthetic arms through an array of electrodes permanently attached to specific parts of their brains. When the monkeys wanted to move the arm, the electrodes converted their brain activity into signals that a computer picked up and then relayed to the prosthetic arm.

And two years ago, researchers implanted an electrode array into a paraplegic man?s head. A docking base of sorts allowed researchers to plug a computer cable directly into the patient?s brain so that he could control a cursor on a computer screen, change the channels on his TV set and control a robotic arm.

While the work done by Fetz and other researchers is promising, it also raises esthetic questions. Specifically, the sight of someone with too many wires running from the brain to various body parts can be jarring. And the wires themselves could become a hazard as people could trip over them or accidentally jerk them out.

One way around the problem would be implanted wireless electrode arrays. Last year, researchers from the Huntington Medical Research Institute demonstrated such a system.

Neural device

The Huntington team implanted a neural device at a certain point in the lower backs of paralyzed cats. When the device was electrically stimulated, the cat could empty its bladder without triggering the sphincter or other peripheral nerves.

The researchers are working toward developing a similar implanted device and remote control system that could help paralyzed humans regain control of their bodily functions.

Such wireless systems also have drawbacks, though. If the implants need to be removed for repair, for example, the patient would need to be operated on. Repeated procedures could cause scarring that would affect the implant?s ability to work.

E-mail the author at massie@massie.com.