Monkeys Use Brain Power to Move Virtual Arms: New Thoughts on Prosthetics

It turns out that even monkeys can use virtual technology. These animals have learned to control the movement of both arms on an avatar using just their brain activity. The findings could help advance efforts to develop bilateral movement in brain-controlled prosthetic devices for severely paralyzed patients.

Millions of people worldwide suffer from sensory and motor deficits caused by spinal cord injuries. That's why researchers are working to develop tools in order to restore patients' mobility and sense of touch. The brain-machine interface approach in particular holds the promise for reaching this goal. Until now, this particular interface could only control a single prosthetic limb. Restoring function to multiple limbs, though, is a crucial part of this type of research.

"Bimanual movements in our daily activities--from typing on a keyboard to opening a can--are critically important," said Miguel Nicolelis, one of the researchers, in a news release. "Future brain-machine interfaces aimed at restoring mobility in humans will have to incorporate multiple limbs to greatly benefit severely paralyzed patients."

In order to work on bimanual movements a bit further, the researchers trained monkeys in a virtual environment. The animals viewed realistic avatar arms on a screen and were encouraged to place their virtual hands on specific targets in a bimanual motor task. The monkeys first learned to control the avatar arms using a pair of joysticks, but were later able to learn to use just their brain activity to move both avatar arms without moving their own arms.

As the animals' performance in controlling both virtual arms improved over time, the scientists saw widespread plasticity in cortical areas of their brains. This suggested that the monkeys' brains may incorporate the avatar arms into their internal image of their bodies.

In fact, the findings suggest that very large neuronal ensembles--not single neurons--define the underlying physiological unit of normal motor functions. Small neuronal samples of the cortex may be insufficient to control complex motor behaviors using brain-machine interface. This, in turn, could inform future research when it comes to creating prosthetic devices.

"When we looked at the properties of individual neurons, or of whole populations of cortical cells, we noticed that simply summing up the neuronal activity correlated to movements of the right and left arms did not allow us to predict what the same individual neurons or neuronal populations would do when both arms were engaged together in a bimanual task," said Nocolelis. "This finding points to an emergent brain property-a non-linear summation--for when both hands are engaged at once."

Currently, the researchers are using the findings in the Walk Again Project, an international collaboration working to build a brain-controlled neuroprosthetic device.