Stimulation for Spinal Cord Injury Individuals

Most individuals with spinal cord injury (SCI) have residual nerve circuits. The investigators aim to strengthen those circuits to improve motor recovery after injury. To do this, the investigators are attempting to pair electrical and magnetic stimulation with physical training targeted toward the connections between nerve circuits. Past studies by other groups have shown that synapse strength can be improved temporarily after a short period of paired stimulation between the brain (motor cortex) and the peripheral nerves serving target muscles - in other words, "Fire Together, Wire Together". The brain's intention to move a muscle can be read by recording surface electrical activity over target muscles (electromyography or EMG). In animal models of SCI, scientists have successfully used target muscle EMG to trigger spinal cord electrical stimulation pulses while the animals perform physical exercises. Using the body's own signals to trigger nerve stimulation is called "closed-loop stimulation". This might be an optimal method to coordinate brain and nerve activity, especially with the clinical advantage of being possible to combine with physical exercise training. However, whether EMG-triggered closed loop stimulation has the same amount of effect when applied non-invasively in humans is still unknown. This proposed study is a proof-of-principle to demonstrate the potential of non-invasive closed-loop stimulation in humans with incomplete cervical SCI. We will test different combinations of triggered and non-triggered electrical and magnetic stimulation, and record the short-term effects on nerve transmission and skilled function of hand muscles. This pilot study will be a foundation for future studies combining EMG-triggered stimulation with long-term physical exercise training.