The study aims to identify neural locus critical for dual-task walking (walking and talking) in individuals with stroke. To achieve this aim, the investigators apply repetitive transcranial magnetic stimulation (rTMS) to different parts of the brain and evaluate the effects of brain stimulation on dual-task walking speed.

This study will enroll 12 individuals with a stroke at least 6 months ago. Participants will be tested across 3 sessions and each session will be approximately 1 week apart from each other. During testing, participants will be asked to walk under two conditions: single- and dual-task conditions. Under the single-task condition, participants walk on a instrumented mat such that their gait performance will be captured. Under the dual-task condition, participants walk on the mat while performing a counting backward task. The walking assessment is followed by a 12 minute non-invasive brain stimulation using high frequency rTMS. Another walking assessment will be conducted right after the brain stimulation session. High frequency rTMS will be applied to different neural loci, namely primary motor cortex (M1), supplementary motor area (SMA), and dorsolateral prefrontal cortex (DLPFC). The walking speed under two different conditions will be compared before and after brain stimulation to different neural loci.

Inclusion Criteria:

1. Age above 18 years
2. Diagnosis of Left hemispheric stroke at least 6 months ago
3. First time stroke OR complete gait recovery from prior stroke
4. Able to walk independently for at least 10 meters with or without walking aids
5. Have at least minimal movements (> 5 degree of motion) at the affected ankle
6. Score > 26 on Mini Mental State Exam (MMSE)
7. Ability to participate in the informed consent process

Exclusion Criteria:

1. Diagnosis of other neurological conditions, such as Parkinson Disease, Alzheimer, Spinal Cord Injury, Multiple Sclerosis
2. Other comorbidities which could interfere with gait (i.e. amputation, severe osteoarthritis)
3. Unstable clinical conditions
4. Non-ambulatory prior to onset of stroke
5. History of significant head trauma
6. Electrical, magnetic, or mechanical implantation: cardiac pacemakers or intracerebral vascular clip
7. Metal implantation in the oral cavity, head/neck area and lower extremity
8. Pregnancy
9. History of seizures or unexplained loss of consciousness
10. Immediate family member with epilepsy
11. Use of seizure threshold lowering medicine
12. Current abuse of alcohol or drugs
13. Anticipated inability to complete the study
14. History of psychiatric illness requiring medication control

3 weeks