One tiny brain cell is all it takes to restore voluntary movement of
paralysed muscles, scientists in the United States reported Wednesday.
In experiments pointing to new treatments for paralysis caused by
spinal cord injury or stroke, monkeys learned within minutes to harness
the power of a single neuron to activate muscles immobilised by drugs.
There are some 100 billion neurons in the human brain, and the study
suggests an unsuspected degree of flexibility in the kinds of tasks
they can perform.
"Nearly every neuron we tested could be used to control this type of
stimulation," Chet Moritz, lead author and a researcher at the
University of Washington, told journalists in a conference call. If a monkey can do it, a human should be able to do it even better, he said.
Clinical trials, however, are at least several years away, perhaps
longer, Moritz added.
What the researchers found
Spinal cord injuries cripple hundreds of thousands of people
worldwide every year, rendering the simplest of actions - opening a
door, scratching an itch, drinking a glass of water - frustratingly
difficult, or simply impossible.
Those afflicted with the most severe form of paralysis, known as
lock-in syndrome, are fully conscious prisoners inside a body that no
longer responds to commands.
While the brain activity that would normally result in a voluntary
movement is still present, the instructions simply don't reach the
Moritz and two colleagues at the University of Washington found a
way to bypass the kind of nerve damage that can result in such
They first connected electrodes to individual neurons inside the
motor cortex of monkey's brain and recorded the electrical activity. These signals were then routed in real-time to a computer, and from there through a stimulator to another set of electrodes attached directly to wrist muscles that had been artificially blocked further up the arm along the normal neural pathway.
Because little processing power is needed, the computer is the size
of a cell phone, and can be attached to the animal's body. Future versions will be wireless and small enough to implant directly in the body, the researchers said.
Brain learns fast
The monkey had already mastered a simple video game, grasping
targets shown on a video screen with a control device manipulated by a
"But once he was paralysed, the only way to move his wrist was to
change the activity of individual neurons in his brain," Moritz
On average it took about 10 minutes for the monkeys to "train" the
neuron well enough to play the video game again. "The brain can very rapidly learn to control new cells and use them to generate movements," said co-author Eberhard Fetz.
Earlier experiments enabling monkeys to manipulate prosthetic
devices or computer cursors using only electrical impulses coming from
the brain were based on a fundamentally different premise, according to
the new study.
"They tried to read the mind of the monkey and figure out what he was
planning to do," a technique that required massive computing power,
"Our approach is to recreate the raw connectivity between single
neurons in the brain and muscles, and let the monkey's nervous system
learn how to use that connectivity."
What the findings mean
This is also the first study to show that a one neuron can control a
muscle - and possibly a whole group of muscles. Electrodes connected to a single location in the spinal cord below an injury may be able to activate 10 or 15 muscles that are already precisely balanced for, say, grasping a coffee mug or walking, the researchers said.
And if a stroke has damaged the motor cortex, patients might be able
to commandeer other brain cells that do not usually play a role in
Several obstacles remain, however, before this new technique can be
tested in humans, he said. To avoid infections, the system would have to become fully implantable so that no wires passed through the skin. And electrodes would need to be made more stable so that they could record the
activity of neurons over a period of years, rather than weeks. – (Sapa, October 2008)
Hope against paralysis
Monkeys control robot with brain