Transcranial Direct Current Stimulation for Post-stroke Gait Rehab

Stroke affects upwards of 800,000 Americans every year and has an enormous impact on the well-being of the American Veteran population with 6,000 new stroke admissions every year. Many of these stroke survivors are living with walking disabilities. Gait problems result in inability to function independently, high risk of falls and poor quality of life. Unfortunately, current gait rehabilitation treatments are limited and many stroke survivors do not achieve full recovery. Therefore, it is critical to develop new approaches to enhance gait rehabilitation methods. The investigators propose to evaluate a brain stimulation treatment called transcranial Direct Current Stimulation (tDCS) that can be added to physical therapy. tDCS has been applied for arm rehabilitation after stroke with positive results, but gait-related investigations are lacking. The investigators will test whether simultaneous tDCS and gait training produces greater improvement in walking abilities than gait training alone. Adjunct tDCS therapy may improve outcomes, and reduce cost of both rehabilitation and post-stroke care.

Current rehabilitation methods fail to restore normal gait for many stroke survivors leading to dependence on others, recurrent falls, limitations in community ambulation and poor quality of life. The main objective of this study is to test both efficacy and neurophysiological mechanisms of a novel approach to treat persistent gait deficits after stroke with a combination of simultaneous non-invasive brain stimulation with transcranial Direct Current Stimulation (tDCS) and gait training. The investigators will enroll chronic stroke subjects (\>6 months) with gait deficits. Subjects will be randomized to 10 sessions of either active tDCS+gait training or sham tDCS+gait training. Gait training will be accomplished in the treadmill-based Virtual Reality environment targeting longer single limb stance with the paretic limb. The primary outcome measure will be both gait speed and single limb stance duration. Other outcome measures will assess various components of gait-related functional domains. The study will also characterize neuroplastic brain changes in response to bihemispheric tDCS combined with gait training based on corticospinal excitability using motor evoked potentials and functional connectivity using resting state functional Magnetic Resonance Imaging (rs-fMRI).

Eligibility Criteria:
Inclusion Criteria:

* Medically and psychologically stable and at least 6 months after first ever unilateral stroke
* Cognition sufficiently intact to give valid informed consent to participate
* FMLE score \>15; and ability to actively dorsiflex the paretic ankle in synergy (FMLE item II Flexor synergy-ankle dorsiflexion score 1).
* Sufficient endurance to participate in the study

Exclusion Criteria:

* Activity tolerance is insufficient to complete treadmill training
* Inability to produce a trace contraction of ankle dorsiflexors in synergy
* Normal ankle dorsiflexion/knee flexion on FMLE standing items (FMLE item IV score=4)
* Stroke affecting both sides
* Contraindications for rTMS according to the most recent TMS-use guidelines
* Contraindications for MRI
* Inability to understand English