For people with cervical SCI, regaining hand function is their highest priority. Most SCIs are motor incomplete, and even when complete, there is often significant amounts of spared spinal cord white matter. The goal of this project is to strengthen residual corticospinal tract (CST) connections after partial injury using combined motor cortex and spinal cord stimulation to improve arm and hand function.~The team's research in rats, which has been refined in over a decade of study, demonstrates that brain and spinal cord stimulation fully restores motor skills in rats after CST injury. Most significant for the population of people living with SCI, this approach is effective in the chronic phase of injury.~Recently, the investigators translated this electrical stimulation protocol into one that can be rapidly translated into people using non-invasive techniques. In rats, combined electrical intermittent theta burst stimulation (iTBS) of motor cortex with transcutaneous spinal direct current stimulation (tsDCS) activates the cervical spinal cord. This protocol, which is administered only 30 minutes a day for 10 days, causes large-scale sprouting of CST connections and full recovery of forelimb function. Thus, by combining brain and spinal cord electrical stimulation in rodents with corticospinal system injury durable CST axonal sprouting, strengthening of CST connections, and recovery is achieved.~In this proposal, the investigators intend to bring this promising therapeutic approach to humans with cervical SCI. The team will study people with chronic, motor incomplete, SCI to test the safety and feasibility of this approach. The investigators' approach is non-invasive and, if shown to be effective, can be rapidly integrated into current clinical practice to help restore hand function in people with chronic SCI.~Each subject will undergo four stimulation sessions of 4 hours or less. Outcomes focus on safety and neurophysiological transmission. The first session is used to determine the target muscle, optimal scalp site for TMS stimulation, assess cervical tsDCS tolerability, and measure maximal contraction force of the fingers, wrist, and elbow. The second through fourth sessions will assess the acute tolerability and effects of tsDCS with different intensities and electrode configurations in a randomized order. Each session will test a different electrode configuration and will be divided into two stages. The first stage will randomly deliver three 5-minute blocks of tsDCS at different randomized intensities (100%, 66% and 0% (sham) of tolerated intensity, as determined in Session 1) and assess changes in corticospinal and spinal excitability in response to TMS and peripheral nerve stimulation (PNS) of the target muscle. The second stage will assess the acute effects of 20-minutes of tsDCS delivered at two thirds the maximal tolerability on TMS- and PNS-evoked responses and performance of a motor task. Safety and tolerability will be closely monitored at all times.
The goal of this project is to strengthen residual corticospinal tract (CST) connections after partial injury using combined motor cortex and spinal cord stimulation to improve arm and hand function after spinal cord injury (SCI).~To do this, the investigators will test the combination of transcranial magnetic stimulation (TMS) with transcutaneous spinal direct current stimulation (tsDCS) in individuals with chronic cervical SCI.