http://www.guardian.co.uk/science/2008/oct/15/spinal-cord-injury-brain-implant

Implant allows monkeys to move paralysed limbs by mind control
More advanced versions of the implant could eventually allow people with 
paraysed legs to walk again, and give paraplegics control over their limbs
  a.. Ian Sample 
  b.. guardian.co.uk, 
  c.. Wednesday October 15 2008 18.03 BST 

 
The late actor Christopher Reeve. The new implant could restore movement to 
people who have sustained major spinal cord injuries. Photograph: Bob Child/AP

A brain implant has allowed paralysed monkeys to move their limbs - by tapping 
into their thoughts and redirecting the signals to their muscles - scientists 
announced today. The feat is being seen as a major development in the hunt for 
treatments for people who have lost the use of their limbs due to major spinal 
cord injuries or strokes. 

Doctors hope the implant will one day allow severely disabled people to use 
mind control to regain movement of their arms and legs.

The work is the first to show that signals from single brain cells can be 
re-routed around damaged areas of the central nervous system, restoring 
function to paralysed limbs. Previously, scientists have shown that monkeys 
fitted with brain implants can move robotic arms or cursors on a screen. 

Scientists involved in the experiments yesterday sought to dampen hopes that 
the technique would be ready to help disabled people in the near future, but 
others said they expected to see the first human trials within five years. More 
advanced versions of the implant could give people with paralysed legs the 
ability to walk again, and eventually give paraplegics control over all their 
limbs, including very precise movements of the hands and arms.

In the study, which appears in the journal Nature, scientists at Washington 
University in Seattle implanted ultra-thin electrodes into the brains of 
macaques trained to play a game that involved rotating their wrist to the left 
and right. While the monkeys played, the electrodes picked up electrical 
signals in their brains that made them tense different muscles.

The scientists then injected the monkeys with a chemical that temporarily 
paralysed their arms. This time, signals from nerves in their brains were fed 
into a computer, cleaned up and magnified, and sent down a wire to muscles in 
the monkeys' wrists.

When the monkeys tried to play the game again, they were unable to at first, 
but soon learned to control their wrist movements using the brain implant. 

Astonishingly, even when the implant was connected to nerves that were not 
involved in wrist control, the monkeys learned how to change their brain 
activity to control the same actions.

"The monkey was experimenting with different types of movement and different 
types of cognitive activity to drive those neurons and when he found something 
worked, he quickly repeated it and adopted the strategy," said Ebehard Fetz, 
who led the study.

Future work on the system will focus on miniaturising the technology and 
developing wireless networks to send the brain's signals around damaged parts 
of the spine to limbs that have lost their connections to the brain.

As it stands, researchers have several major hurdles to overcome before the 
technique could safely be used in humans. The first is to remove the need for 
wires, which increase the risk of infection. The second problem is that when 
electrodes are put into the brain, they gradually become encapsulated in scar 
tissue, which reduces their ability to read signals from individual neurons. 
The latest study suggests, though, that as long as the electrodes have a good 
contact with at least one neuron, it will still be possible to control muscle 
movements.

Chet Moritz, who worked on the study, said the team is looking at another 
potentially more powerful way of using the implant to control paralysed limbs. 
Instead of re-directing brain signals to individual muscles in a limb, they can 
be sent into the spinal cord to stimulate several nerves that together trigger 
a group of muscles to do a specific job, such as grasp a mug, or kick a ball. 

"If you stimulate directly in the spinal cord, that will often activate 10 to 
15 muscles in a precise balance that produces a grasping movement or a stepping 
movement," Moritz said.

Lee Miller at Northwestern University in Chicago, who recently showed how 
monkeys could control their limbs using signals from bunches of brain cells, 
said: "This is the first instance when activity from a single neuron in the 
brain has been used to control a paralysed limb rather than a robotic arm or a 
cursor on a screen. I'd certainly hope that within the next five years there 
will be at least experimental applications being tried out in humans."

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