In experiments published in the June 7 issue of the journal Science, monkeys were able to move balls around in 3D space on a computer screen just by thinking about it. With a little practice, they got even better at it.
"They achieved nearly the same accuracy and speed as normal arm movements," said senior author Andrew Schwartz, Ph.D., of the Department of Bioengineering at Arizona State University and the Neurosciences Institute in San Diego.
To begin with, two monkeys learned a computer game that required moving balls around in 3D space on the screen. The balls moved in response to the monkeys' arm movements. The monkeys were rewarded for playing and were allowed to stop when they tired of it.
Then tiny electrodes were painlessly implanted in the monkeys' brains to record the motor control signals emitted when they moved their arms to play the game. The recorded signals were matched against specific arm/ball movements.
Finally, the monkeys were encouraged to play the game without using their arms. They had to move the balls on the screen using brain signals that corresponded with the appropriate arm movements.
At first they tried to use their arms. But as they realized they could move the balls without moving their arms, they relaxed their arms and continued the game using thought control. As they played, their game skills improved.
Controlling the movement of a prosthetic limb, however, would require learning a wider range of movements, so the two monkeys were given new tasks and 180-degree changes in directions.
"There was no significant difference between the novel and trained target hit rates in either animal, and both monkeys improved their performance with daily practice," the researchers reported.