Engineers have developed remarkable devices that allow patients with paralysis to regain control of hand movements and to achieve a greater measure of independence in daily activities. The technology, called functional electrical stimulation (FES), can already be used to restore movements to paralyzed limbs by directly stimulating muscles.

These systems rely on movement of other parts of the limb that are still functional, such as a shrug of the shoulders, which is not possible in all patients. Furthermore, most systems can only produce one or two types of movements, rather than being able to mimic the complexity of normal hand movements. L.E. Miller and colleagues at Northwestern University (Chicago, IL) have now developed an FES system that can directly use signals from the brain to control movements.

Credit: beemore at iStockPhoto.com

They first trained two rhesus macaques to pick up a ball and put it in a dispenser. After the monkey had learned the behavior, each monkey was implanted with a multi-electrode recording array in the hand area of the motor cortex. More electrodes were implanted in the muscles of the hand and forearm for recording and stimulation.

While the monkeys were performing the trained behavior, the researchers simultaneously recorded the activity in the hand and arm muscles as well as the neurons in the motor cortex. These recordings were used to build a decoder, which could be used to translate the commands being relayed from the motor cortex to the electrodes to stimulate the appropriate muscles in the arm (Nature doi:10.1038/nature10987; published online 18 April 2012).

To test the decoder, they blocked the nerves in the arm and hand to induce temporary paralysis. When the prosthetic equipment was turned off, the monkeys were no longer able to even pick up the ball. When the equipment was turned on, however, the implanted device relayed the messages from the brain to the electrodes in the arm muscles through wires, bypassing the blocked nerves and restoring the monkeys' ability to pick up the ball and put it in the dispenser.

While the model of paralysis used in this study avoided some of the complications of actual spinal cord injury, such as denervation of paralyzed muscles, the scientists hope that their system could be used to help people with spinal cord injuries regain some control over their hands. Miller told The Scientist, “There are really no significant technical hurdles that would prevent us from taking this combined technology to humans.”