Funded by the National Institutes of Health (NIH), the study may have promising implications for those affected by spinal cord injuries and thousands of others with paralyzing neurological diseases.
"This study demonstrates a novel approach to restoring movement through neuroprosthetic devices, one that would link a person's brain to the activation of individual muscles in a paralyzed limb to produce natural control and movements," Nature magazine quoted Dr. Joseph Pancrazio, a program director at the National Institute of Neurological Disorders and Stroke (NINDS), as saying.
For their study, the researchers trained monkeys to control the activity of single nerve cells in the motor cortex, an area of the brain that controls voluntary movements.
The team used a type of brain-computer interface to detect neuronal activity. They connected electrodes implanted in the motor cortex were connected via external circuitry to a computer.
The neural activity led to movements of a cursor, as monkeys played a target practice game.
Once the monkeys had mastered control of the cursor, their wrist muscles were temporarily paralyzed using a local anesthetic to block nerve conduction.
The team then converted the activity in the monkey's brain to electrical stimulation delivered to the paralyzed wrist muscles.
The monkeys continued to play the target practice game, demonstrating that they had regained the ability to control the otherwise paralyzed wrist.
"A robotic arm would be better for someone whose physical arm has been lost or if the muscles have atrophied, but if you have an arm whose muscles can be stimulated, a person can learn to reactivate them with this technology," says lead researcher Dr. Eberhard E. Fetz, professor of physiology and biophysics at the University of Washington in Seattle.
The researchers believe that a connection between the motor cortex and sites in the spinal cord below the injury may enable those with spinal injuries to achieve coordinated movements.
Dr. Fetz, however, insists that clinical applications are still at least a decade away because they would require better methods for recording cortical neurons, for controlling multiple muscles, and implantable circuitry that could be used reliably and safely.