"Practice makes perfect" is the maxim drummed into students struggling to learn a new motor skill - be it riding a bike or developing a killer backhand in tennis.

Stunning new research now reveals that the brain can also achieve this motor memory with a prosthetic device, providing hope that physically disabled people can one day master control of artificial limbs with greater ease.

The study, conducted by scientists at the University of California, Berkeley, addresses a fundamental question about whether the brain can establish a stable, neural map of a motor task to make control of an artificial limb more intuitive.

"When your own body performs motor tasks repeatedly, the movements become almost automatic," said study principal investigator Jose Carmena, a UC Berkeley assistant professor with joint appointments in the Department of Electrical Engineering and Computer Sciences, the Helen Wills Neuroscience Institute, and the Program in Cognitive Science.

"The profound part of our study is that this is all happening with something that is not part of one's own body. We have demonstrated that the brain is able to form a motor memory to control a disembodied device in a way that mirrors how it controls its own body. That has never been shown before."

Researchers in the field of brain-machine interfaces, including Carmena, have made significant strides in recent years in the effort to improve the lives of people with physical disabilities. An April 2009 survey by the Christopher and Dana Reeve Foundation found that nearly 1.3 million people in the United States suffer from some form of paralysis caused by spinal cord injury. When other causes of restricted movement are considered, such as stroke, multiple sclerosis and cerebral palsy, the number of Americans affected jumps to 5.6 million, the survey found.

Already, researchers have demonstrated that rodents, non-human primates and humans are able to control robotic devices or computer cursors in real time using only brain signals. But what had not been clear before was whether such a skill had been consolidated as a motor memory. The new study suggests that the brain is capable of creating a stable, mental representation of a disembodied device so that it can be controlled with little effort.

To demonstrate this, Carmena and Karunesh Ganguly, a post-doctoral fellow in Carmena's laboratory, used a mathematical model, or "decoder," that remained static during the length of the study, and they paired it with a stable group of neurons in the brain. The decoder, analogous to a simplified spinal cord, translated the signals from the brain's motor cortex into movement of the cursor.

It took about four to five days of practice for the monkeys to master precise control of the cursor. Once they did, they completed the task easily and quickly for the next two weeks.

"In experiments that involved moving a cursor from a central starting point to a nearby target, researchers found that the brain is capable of creating a stable mental representation of a disembodied device. (Credit: Copyright John Blanchard illustration)"

Source: University of California - Berkeley