November 8, 2013
Monkeys have been given the ability to control two virtual arms simultaneously using thought alone. The same technology might soon give people who are paralysed control of an exoskeleton that they can move with their mind.
Monkeys and humans have previously controlled a single prosthetic arm using their thoughts. It is done using electrodes placed in the brain, which recognise specific patterns of electric activity that occur when a person thinks about moving. This pattern is then translated into actual movement in the prosthesis.
Until now, though, it has only been possible to control a single limb this way. That is because when the brain thinks about moving both arms at once, the activity is not merely a sum of what you might see if you moved each arm individually, but a completely different pattern.
To achieve such bimanual movement, Miguel Nicolelis at Duke University in Durham, North Carolina, and his colleagues recorded the individual electrical activity from almost 500 single neurons in the somatosensory and motor cortex on both sides of a monkey’s brain, the areas responsible for sensing body position, touch and movement.
“We believe it’s the largest number of neurons simultaneously recorded in a non-human primate,” says Nicolelis.
While they recorded brain activity, the team trained the monkey to move the hands of a virtual representation of itself to follow two moving targets on the screen (see video, above).
This involved first teaching the monkey how to move its avatar’s virtual hands using two joysticks. While this was going on, the team’s computer algorithm learned which brain activity matched which movements.
Once this was achieved, the joysticks were disconnected and the algorithm took over. When the program detected a pattern in the monkey’s brain signalling the intention to move, it moved the virtual hands in the corresponding direction. The monkey was rewarded each time the hands met the target, so it quickly learned to move the hands with thought alone.
“Then we tried something more adventurous,” says Nicolelis. The team had shown that an algorithm could be trained to recognise the intention to move both hands, but the next step was to see whether they could train the algorithm without the monkey initially using its own arms.
This part of the experiment is crucial, because it demonstrates that the algorithm can be trained using thoughts alone — a vital step if people without the use of their limbs are to use the technology.
Travelling without moving
To do this, the team had a second monkey watch the virtual arms moving towards targets while its own arms were gently restrained.
As the monkey watched, its neurons in the motor and somatosensory cortex began to react in much the same way as they might have if the monkey have been moving its own arms.
It took just 7 minutes for the algorithm to recognise the patterns of brain activity that correlated with the movement of the virtual hands. After this time, the researchers allowed the algorithm to take over — only moving the hands when the monkey thought about moving them.
The research is part of the Walk Again Project, an international collaboration to create an exoskeleton that disabled people could control with their mind.
Nicolelis’s team has already built a virtual environment in which paralysed people can train to move virtual avatars. This should eventually prepare them to move a thought-controlled exoskeleton, which Nicolelis’s team hopes to showcase at the opening ceremony for the 2014 football world cup in Brazil.