The study was terminated due to administrative and logistical constraints following the Principal Investigator's transfer to another institution.

The goal of this study is to test the effects of non-invasive electrical stimulation of the spinal cord (called transcutaneous spinal cord stimulation, or tSCS) on arm and hand movement in people with motor impairments after a traumatic brain injury (TBI). Specifically, tSCS will be delivered using adhesive electrode pads placed on the skin over the upper back. The research team will measure how tSCS affects strength, movement control and muscle spasticity using different tests. Results of this study will help develop future treatments using an implanted (invasive) form of spinal cord stimulation to improve arm and hand function, helping people with TBI become more independent and improve their quality of life.

The main goal of this study is to assess the immediate effects of cervical transcutaneous spinal cord stimulation (tSCS) on arm and hand motor functions after traumatic brain injury (TBI). Specifically, the investigators will assess the immediate effects of tSCS across four different axes: arm and hand strength, arm motor control, joint synergies and spasticity.

The study hypothesis is that tSCS can immediately facilitate voluntary motor output of upper limb muscles by modulating residual descending drive to spinal motoneurons in TBI individuals. In this approach, tSCS targets large-diameter sensory fibers projecting onto motor neuron pools of upper limb muscles. Thus, by modulating the activity of these sensory fibers, the investigators hypothesize that tSCS can immediately increase the excitability of motoneurons receiving residual supraspinal input during movement execution.

Upon completion of this study, the investigators expect to build foundational evidence supporting the use of invasive (e.g. epidural spinal cord stimulation) and non-invasive SCS (tSCS) to improve upper limb motor function in individuals affected by chronic motor impairments after TBI. These results will lay the groundwork for future studies aimed at developing SCS neuroprosthetic devices.

Inclusion Criteria:

TRAUMATIC BRAIN INJURY (TBI) SUBJECTS:

• Participants must have a suffered a traumatic brain injury resulting in impairments in arm and hand motor function at least one year prior to enrollment.
• Participants must be between the ages of 21 and 70 years old.

HEALTHY CONTROL SUBJECTS:

• Participants must have full range of motion in their upper limbs;
• Participants must be between the ages of 21 and 70 years old.

Exclusion Criteria:

TRAUMATIC BRAIN INJURY (TBI) SUBJECTS:

• Participants with severe behavioral or cognitive impairments (e.g., aphasia, apraxia, visual neglect) that could preclude their ability to participate in the study.
• Participants diagnosed with Paroxysmal Sympathetic Hyperactivity (PSH);
• Participants with post-TBI heterotopic ossification or tendon contractures that restricts passive range of motion of upper limb joints;
• Participants with uncontrolled epilepsy or untreated seizure disorders;
• Participants with implanted electronic devices, such as pacemakers and spinal cord stimulators;
• Participants taking benzodiazepine for spasticity;
• Participants with serious disease or disorder (ex. neurological condition other than TBI, cancer, severe cardiac or respiratory disease, renal failure, etc.) that could affect their ability to participate in this study.
• Female participants must not be pregnant or breast feeding.
• Evaluation to sign consent form score <12.

HEALTHY CONTROL SUBJECTS:

- Participants who have any serious disease or disorder (e.g. cancer, severe cardiac or respiratory disease, neurological conditions, etc.) or cognitive impairments that could affect their ability to participate in this study.

Data may be shared with other researchers for the purpose of data analysis and collaboration.