Researchers in a study funded by the National Institutes of Health (NIH) have demonstrated for the first time that a direct artificial connection from the brain to muscles can restore voluntary movement in monkeys whose arms have been temporarily anesthetized. The results may have promising implications for the quarter of a million Americans affected by spinal cord injuries and thousands of others with paralyzing neurological diseases, although clinical applications are years away.
"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," said Joseph Pancrazio, Ph.D., a program director at the National Institute of Neurological Disorders and Stroke (NINDS).
The research was conducted by Eberhard E. Fetz, Ph.D., professor of physiology and biophysics at the University of Washington in Seattle and an NINDS Javits awardee; Chet T. Moritz, Ph.D., a post-doctoral fellow funded by NINDS; and Steve I. Perlmutter, Ph.D., research associate professor. The results appear in the online Oct. 15 issue of Nature. The study was performed at the Washington National Primate Research Center, which is funded by NIH's National Center for Research Resources.
In the 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. Neuronal activity was detected using a type of brain-computer interface. In this case, 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.
After each monkey mastered control of the cursor, the researchers temporarily paralyzed the monkey's wrist muscles using a local anesthetic to block nerve conduction. Next, the researchers 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 - only now cursor movements were driven by actual wrist movements - demonstrating that they had regained the ability to control the otherwise paralyzed wrist.
The group's approach is one of several lines of current neuroprosthetic research. Some investigators are using brain-computer interfaces to record signals from multiple neurons and convert those signals to control a robotic limb. Other researchers have delivered artificial stimulation directly to paralyzed arm muscles in order to drive arm movement - a technique called functional electrical stimulation (FES). The Fetz study is the first to combine a brain-computer interface with real-time control of FES.
"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 Dr. Fetz.