Stroke is a leading cause of long-term disabilities in the U.S., which can markedly impact the function of the upper extremity (UE). One of the major UE motor impairments is abnormal intermuscular coordination, which leads to impaired post-stroke function and life participation. Also, relatively little is understood about how stroke affects the corticospinal innervation of multiple UE muscles, visualized as multi-muscle motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) of the primary motor cortex (M1), and its association with intermuscular coordination and impaired UE motor function in stroke. Some studies have shown that improvement in corticospinal excitability for the affected limb may be able to improve intermuscular coordination and enhance motor function recovery after stroke. Operant conditioning is a method that can be used to produce not only targeted plasticity but also wider beneficial plasticity in multiple spinal/supraspinal pathways. Recent studies have shown that MEP operant up-conditioning can increase the corticospinal excitability for the targeted muscle in people with SCI in the UE and lower extremity (LE) and in the LE of multiple sclerosis.~For the aim 1 of the project, MEPs elicited by TMS will be applied at the hot spot for the wrist ECR. EMG signal from 15 UE muscle will be collected simultaneously during isometric force generation tasks. This aim will enroll 10 age-matched (age of 40-75 yo) healthy adult and 10 adult (age of 40-75 yo) stroke survivors. Each participant will have a single measurement session.~For the aim 2 of the project, 4 randomized out of 10 stroke survivors will perform operant conditioning method of the wrist ECR; also, assessment of the intermuscular coordination, UE Fugl-Meyer (FM), and Action Research Arm Test (ARAT) will be performed. Participants will have three visits per week for 10 weeks for training session. Finally, to test retention of the intervention effect, they will perform two assessment sessions one and three months after finishing the training.
The purposes of this study include:~To test if multiple upper extremity muscles represented within a discrete primary motor cortex site reflect existing muscle synergies after stroke.~To test if altered muscle synergies and intermuscular coordination are malleable to motor evoked potential conditioning that induces corticospinal plasticity for the targeted muscle, wrist extensor carpi radialis