Motoneuron Recruitment and Motor Evoked Potential Up-Conditioning (MEP) in Spinal Cord Injury (SCI)

Overview

The purpose of this research study is to examine the effect of a brain stimulation training to improve the function of brain-spinal cord- muscle connections. Because brain-to-muscle pathways are very important in our movement control, restoring function of these pathways may improve movement problems after injuries. Spinal cord injury causes damage to the brain-to-muscle connection. However, when the injury is "incomplete", there is a possibility that some of the brain-to-muscle pathways are still connected and may be trained to improve movement function. For examining brain-to-muscle pathways, investigators use a transcranial magnetic stimulator. Investigators hope that the results of this research study will help us develop new treatments for people who have movement disabilities. This study will require about 42 visits over the first 14 weeks, and another 6 visits over an additional 3 months. Each visit will take about 1 ½ hours.

Regaining arm/hand function is one of the top priorities of individuals with tetraplegia and is a challenging problem, partly due to the complex nature of upper limb motor function. Through mass practice and conventional therapy, functions can be restored partially, likely through compensation rather than induction of relevant corticospinal plasticity. In such cases, corticospinal recruitment of motoneurons and resulting muscle activation could remain impaired and continue to limit function recovery. In people with incomplete SCI, voluntary activation of the muscles below the injury level is often diminished, due at least partly to impaired motor unit behaviors. Abnormal motoneuron recruitment and motor unit firing, also found in other CNS disorders, would certainly hinder effective production of motor functions. Thus, to enhance upper limb motor rehabilitation beyond what conventional therapy has been able to achieve, a method to improve corticospinal recruitment of a targeted pool of motoneurons would be needed. Here, investigators hypothesize that wrist extensor MEP up-conditioning can improve forearm motor functions in people with cervical SCI by increasing the corticospinal excitability and improving corticospinal recruitment of wrist extensor motoneurons.