Scientists in the US have successfully shown it is possible for a monkey to move a paralysed wrist via a connection made directly into the brain, that is allowing electrical signals from the brain to be routed to the wrist directly without using normal nerve pathways down the arm.
The experiment was performed by Dr Chet Moritz and colleagues at the University of Washington in Seattle and was published online on 15th October in the journal Nature.
Previous experiments have shown it is possible for monkeys to move robotic arms connected directly to their brains. These rely on a powerful computer to decode neuron signals into a range of actions such as grasping. One such study was carried out by Dr Andrew Schwartz, a neurobiologist at the University of Pittsburgh in Pennsylvania, and colleagues, who published their findings in Nature earlier this year.
But in this experiment, Moritz and his team used a similar method to route electrical signals from one neuron to a paralysed muscle.
In the first stage of the experiment they implanted electrodes into the motor cortex of the brain of two live monkeys, whereby each electrode relayed signals from a single neuron through an external circuit to a computer. The monkeys learned to control the cursor on the computer screen via this single neuron circuit.
In the second stage of the experiment, using a local anaesthetic, Moritz and colleagues temporarily paralyzed the monkeys’ wrist muscles and wired them up to the single neuron circuit. It took the monkeys less than an hour to learn how to control their paralysed wrists using the same brain activity that they had previously used to control the cursor on the computer screen.
What was astonishing about this finding was that any neuron could be used; regardless of what function that neuron was performing before it was “retrained”.
“All neurons could be used equally well, regardless of whether that neuron was originally related to the activity of these muscles,” said Moritz.
“This dramatically expands the potential population of neurons that could be used to control a neural prosthesis,” he added.
Commenting on this latest study, Schwartz said he was amazed by the way the neurons could change the way they related to the outside world.
“There’s an amazing flexibility in the way that the system can learn,” he told NatureNews.
Moritz’s co-author Dr Eberhard Fetz showed how neurons could be used to control actions back in the 1970s, but this latest work is remarkable because it shows how flexible neurons are, and how quickly the monkeys learned to use the same neuron to control their own muscles.
It will be some time before this discovery translates into treatments for humans with paralysed limbs said the researchers. There is a big difference between a monkey using one neuron to control one activity using a short term electrode implant and a human using a long term implant to perform whole actions and co-ordinated movements.
“Multi-joint movement is orders of magnitude more complicated than this demonstration,” said Moritz.
Another leap forward in this experiment was the elimination of a high powered computer. Because the connection was made directly into the brain, the only processing power necessary was a battery-powered chip the size of a cellphone. The researchers imagine this will be even smaller in the future, perhaps small enough to fit in a shirt pocket or even go under the skin like a pacemaker, said Moritz.
“Direct control of paralysed muscles by cortical neurons.”
Chet T. Moritz, Steve I. Perlmutter & Eberhard E. Fetz.
Nature, Published online 15 October 2008
doi:10.1038/nature07418
Source: Nature.
Written by: Catharine Paddock, PhD.