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Monkeys Use Mind Power To Move Paralyzed Limbs

October 15, 2008

Scientists have demonstrated that it is possible to harness brain signals and redirect them to make paralyzed limbs move.

The technology bypasses injuries that stop nerve signals traveling from the brain to the muscles, offering hope for people with spinal damage.

So far, it has only been tested on “brain-machine interfaces” in monkeys, the US team from the University of Washington said.

But they are hoping to develop implantable circuits for humans without the need for robotic limbs, Nature reports.

Those suffering from spinal chord injuries have impaired nerve pathways between the brain and the limbs but are spared both the limb muscles and the motor cortex””the part of the brain that controls movement.

Previous studies have shown that quadriplegic patients – people who have paralysis in all four limbs – can consciously control the activity of nerve cells or neurons in the motor cortex that command hand movements, even after several years of paralysis.

Dr. Chet Moritz and colleagues used a device called a brain-machine interface and re-routed motor cortex control signals from the brains of temporarily paralyzed monkeys directly to their arm muscles.

The mobile phone-sized device interprets the brain signals and converts them into electrical impulses that can then stimulate muscle to contract.

By wiring up artificial pathways for the signals to pass down, muscles that lacked natural stimulation after paralysis with a local anesthetic regained a flow of electrical signals from the brain.

The researchers said the monkeys were then able to tense the muscles in the paralyzed arm, a first step towards producing more complicated goal-directed movements, such as grasping a cup or pushing buttons.

“This could be scaled to include more muscles or stimulate sites in the spinal cord that could activate muscles in a coordinated action,” said Moritz.

“Similar techniques could be applied to stimulate the lower limb muscles during walking.”

The monkeys could learn to use virtually any motor cortex nerve cell to control muscle stimulation – it did not have to be one that would normally controlled arm movement. And their control over the muscles improved with practice.

But treatment could be decades away, as the researchers say they need to do trials in humans.

“This is clearly a step in the right direction and proves the principle that artificially transducing the will to move generated in the brain with relevant motor activity can be achieved,” said Dr. Mark Bacon, head of research at the UK charity Spinal Research.

“However, these results have been produced in experimental models where there is no injury per se.”

Injury-induced changes to the nerve circuits might hinder the technology’s application in real life, Bacon warned.

Also, brain-machine interfaces communicate in only one direction – in this case from the brain to the muscle.

He said sensory feedback, which is so important for fine control of movements and dexterity, is still some way away.

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