Jessica Hamzelou (New Scientist)-A single session of nerve stimulation has improved the movement of people with spinal cord injuries. Mimicking the passage of nerve signals by stimulating a muscle as well as the brain has boosted recovery and helped people to regain better control of their movements.
Voluntary movement requires a signal from the brain, which is passed down the spinal cord and then to neurons in muscles. Damage to the spinal cord can interrupt this pathway, resulting in paralysis.
To improve the control of movement in people with these injuries, Monica Perez and Karen Bunday at the University of Pittsburgh in Pennsylvania used electrical and magnetic stimulation to strengthen the connection between two nerves involved in voluntary movement of the index finger.
The pair used transcranial magnetic stimulation (TMS), a non-invasive technique in which a magnetic field alters brain activity, to target the corticospinal tract. This bundle of nerves connects movement-associated parts of the brain with the spinal cord.
“The corticospinal tract plays a major role in the recovery of motor function in spinal cord injury,” says Perez.
Just 1 to 2 milliseconds after stimulating the brain, they used an electrode to stimulate a nerve that innervates an index-finger muscle – mimicking normal brain-to-muscle nerve signalling.
Perez and Bunday tested the method on 19 people with spinal cord injuries, all of whom retained some degree of voluntary movement.
After 17 minutes of stimulation, “we saw an increase in muscle activity and force of between 20 and 40 per cent”, says Bunday.
The treatment also seemed to improve dexterity. People could place small pegs into holes about 15 per cent faster than they could before they had received the stimulation. The effect lasted for 80 minutes.
The new protocol could also enhance voluntary movement in other motor disorders affecting the corticospinal tract, such as stroke, says Perez.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2012.10.046