Neuromodulation to Improve Grasping Function After SCI

The goal of this study is to restore the activities of late descending signals with a noninvasive stimulation approach in combination with hand motor training to improve hand function in persons with cervical SCI. The main question it aims to answer is if the inputs to late descending signals above the level of injury and the output of residual late descending signals below the level of injury could be increased. Specifically, in the first part of the study, 30 participants will complete 2 randomized sessions to compare the effect of intermittent theta burst stimulation combined with paired corticospinal motoneuronal stimulation. In the second part of the study, 24 participants will complete either combined stimulation protocol or sham stimulation protocol with exercise training.

The investigators will use paired corticospinal-motoneuronal stimulation (PCMS) in combination with intermittent theta burst stimulation (iTBS). During PCMS, the investigators will use paired stimulation of the primary motor cortex by transcranial magnetic stimulation to elicit late corticospinal descending volleys and the peripheral nerve by electrical stimulation to improve corticospinal transmission and functional recovery in humans with cervical incomplete SCI. In addition, the investigators will investigate how priming iTBS affects neuroplasticity of late corticospinal descending volleys. The investigators will apply iTBS on primary motor cortex prior to paired stimulation with PCMS to facilitate late corticospinal volleys and potentiate the effect of PCMS. In Aim 2, the investigators propose to combine our neuromodulation in Aim 1 with long-term motor training focused on hand grasping to strengthen spared connections and promote functional improvement in humans with cervical incomplete SCI.

Inclusion Criteria: For individuals with SCI: * Ages 18-75 years * Chronic SCI (≥1 year of injury) * Cervical injury at C8 or above * Individuals who have MEP responses in at least one FDI muscle Exclusion Criteria: * Uncontrolled medical problems including pulmonary or cardiovascular disease * Premorbid, ongoing major depression or psychosis, altered cognitive status * History of head injury or stroke * Metal plate in skull * History of seizures * Receiving drugs acting primarily on the central nervous system, which lower the seizure threshold such as antipsychotic drugs * Pregnant females * Individuals who suffer from a spinal cord disease such as spinal stenosis, spinal bifida or herniated cervical