Technology is still in its infancy, scientists say, but it's a breakthrough for paralyzed people to regain motion control.
American scientists have announced that they were able to get one monkey to control the movements of another's arm with thought.
Brain readings of the first monkey, called the master, were used as a guide to electrically stimulate the second monkey's spinal cord, called the avatar. Thus, the master could command the avatar movements.
The team of scientists hopes the method will be refined to allow paralyzed people to regain control of their bodies. Spinal cord damage can disrupt the flow of information between the brain and body and prevent a person from walking or eating alone. Researchers seek to circumvent this damage with the help of machines.
Published in Nature Communications, the results of the study were described as "an important step" toward this goal.
In their research, scientists at Harvard Medical School refused to provoke a monkey's palsy because they considered the attitude unjustifiable. Instead, they used two monkeys: a master and an avatar, which was sedated to simulate the effects of paralysis.
A chip was implanted in the master's brain to monitor any brain activity involving more than 100 neurons. During training, the master's movements were related to patterns of electrical activity generated by his neurons.
In turn, the avatar had 36 electrodes implanted in his spinal cord. Tests were performed to verify how the stimulus provoked by different electrode combinations affected their movements.
Only then were the monkeys connected to each other so that their brain readings generated movements in each other in real time. The avatar held a control that commanded a cursor on a screen while the leader thought of moving that cursor up and down.
In 98% of tests, the master can control the movements of the avatar's arm.
"Our hope is to get a totally natural move," researcher Ziv Williams told the BBC. "I think theoretically it is possible, but to reach this point will require additional and exponential efforts."
For Williams, even the slightest ability to move again would dramatically change the quality of life of paralyzed people.
Reality or fiction?
The idea of a brain controlling an avatar's body has been the subject of Hollywood movies, such as Avatar (2009). However, Professor Christopher James of Warwick University rules out a future in which it will be possible to command the bodies of others through thought.
"The risk of this happening is nil," said James. "Even attached to someone else that way, who has no spinal cord or brainstem injury would still retain control of their limbs. So no one will be able to move anyone against their will anytime soon."
Even so, James says, the research has major implications, "especially in limb control when there is an injury or in the control of prostheses by those with an amputated limb."
There are still some challenges to reach this goal. Moving a cursor up and down does not match, for example, the complexity of a movement such as bringing a glass to your mouth.
In addition, muscles tend to become stiffer after paralysis and blood pressure varies greatly, which makes regaining control of the body more difficult.
"This work is an important step forward because it shows that there is a chance to use machine-brain connections to reestablish a paralyzed person's ability to perform movement," says Professor Bernard Conway, chief of biomedical engineering at Strathclyde University. (UK).
"However, much work will be needed before the technology can be used by those who need it."