Transcutaneous electrical stimulation (tcES) of the spinal cord has shown great promise in restoring upper extremity function after spinal cord injury (SCI). More recently, the use of invasive, epidural electrical stimulation of the spinal cord has also demonstrated promise in restoring upper extremity function post-stroke. However, the effect of stimulation parameters such as electrode configuration and stimulation frequency on excitability of the nervous system remains unknown preventing the opportunity to fully exploit this noninvasive stimulation paradigm. Additionally, the utility of noninvasive tcES in the stroke population remains unexplored. This project utilizes a comprehensive set of neurophysiological techniques, in combination with carefully chosen motor tasks, to directly link and assess the effects of stimulation parameters on neural excitability and upper extremity function during and following the delivery of cervical tcES in individuals with SCI and stroke. The fundamental knowledge gained from this project will ultimately improve the implementation of this novel and non-invasive neuromodulatory tool through an improved understanding of how tcES can facilitate recovery of function.

In the first two aims of this study we explore the effects of stimulation configurations on neural excitability. Specifically we will explore the effects of electrode placement and stimulation frequency on measures of corticospinal and intracortical excitability. In the last aim of this study, individuals will participate in an interventional trial combining activity-based therapy with tcES. We will explore whether this intervention facilitated improvements in upper extremity function through clinical and neurophysiological assessments.

Inclusion Criteria:

SCI cohort:

• individuals aged 18 to 75 years of age who have suffered a spinal cord injury
• cervical level injury (C3 to C8)
• at least 1-year post-injury
• for individuals taking medications for spasmolysis or muscle relaxation (e.g. oral baclofen, tizanidine, dantrolene, vigabatrin, gabapentin, or benzodiazepine), dose and regimen must be stable for at least 4 weeks prior to screening

Stroke cohort:

• individuals aged 18-75 years of age who have suffered any type of stroke resulting in upper extremity motor dysfunction with partially preserved motor function
• ≥ 6 months post-stroke
• At least 4 months since last BoNT injection for treatment of spasticity or any other condition or ≤ 2 months after study completion
• for individuals taking medications for spasmolysis or muscle relaxation (e.g. oral baclofen, tizanidine, dantrolene, vigabatrin, gabapentin, or benzodiazepine), dose and regimen must be stable for at least 4 weeks prior to screening

Exclusion Criteria:

• pregnant women
• aphasia or dysphasia
• spasticity grade Modified Ashworth Scale ≥ 3

Transcranial magnetic stimulation-specific exclusion criteria (both cohorts)

• participants with active or inactive implants including cardiac pacemakers, implantable defibrillators, ocular implants, deep brain stimulators, vagus nerve stimulator, and implanted medication pumps
• participants with conductive, ferromagnetic or other magnetic-sensitive metals implanted in their head
• participants with a history of seizures or epilepsy
• participants taking any medication which may reduce seizure threshold

We do not plan to shared IPD with other researchers. Deidentified data may be shared with a data repository.