A method combining transcranial magnetic stimulation with electrical stimulation of peripheral nerves in the wrist temporarily improves hand use in spinal cord injury patients, show research findings published in Current Biology.
"This approach builds on earlier work and highlights the importance of the corticospinal tract - which conducts impulses from the brain's motor cortex to the spinal cord and is a major pathway contributing to voluntary movement - as an important target for intervention after spinal cord injury," said study author Monica Perez (University of Pittsburgh, Philadelphia, USA) in a press statement.
Perez and co-author Karen Bunday, also from the University of Pittsburgh, recruited 19 people with chronic cervical spine injury and 14 uninjured volunteers to take part in a study to test the effects of noninvasive nerve stimulation on hand movement and dexterity.
The cranial and wrist electrodes were positioned in an individualized way in each participant and 100 paired pulses were transmitted every 10 seconds for 20 minutes in total.
The team found that the timing of the impulses was very important, as arrival of presynaptic volleys or stimulation before discharge of the motorneurons improved transmission of the nerve impulse to the hand and allowed the patients with spinal cord injury greater voluntary hand movement.
"This short, noninvasive stimulation protocol has the potential to be used within a clinic setting as part of a rehabilitation technique," said Bunday.
"When pulses from the motor cortex were precisely timed to arrive at the spinal cord one or two milliseconds before pulses from the peripheral nerve, we observed an increase in spinal cord transmission and voluntary motor output for up to 80 minutes."
Improved hand muscle use was seen in the majority of spinal cord injury and control patients (mean muscle force over 120% that of baseline in controls and spinal cord patients after 20 minutes stimulation). In a test for manual dexterity, involving removing small pegs from a board and placing them in a bowl, most of the participants scored higher in the period after stimulation than before.
"Human electrophysiology can be a powerful tool for developing therapies," Perez concluded.
"We need to explore new targets to improve rehabilitation strategies by taking advantage of our knowledge in human physiology and their mechanisms."
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