Stroke is the leading cause of disability and diminished quality of living that frequently includes impairments of postural control and upper extremity (UE) function. The interaction of posture and UE coupling in terms of movement planning, initiation, and execution is not well understood. StartReact responses triggered by a loud acoustic stimulus (LAS) during the planning and preparation of goal intended actions has been used to probe the state of brainstem neuronal excitability related to posture and movement sequencing. The purpose of this study is to examine posture and goal-directed movement planning and execution using startReact responses and to evaluate posture and UE movement sequence during reaching while standing in individuals with chronic hemiparesis and healthy controls. Secondly, the investigators will determine the modulatory role of the cortical premotor areas (PMAs) in startReact responses in healthy controls and in persons with stroke by using transcranial direct current stimulation (tDCS) to up- or down-regulate PMAs excitability.

Inclusion Criteria for stroke:

• Unilateral cortical or white matter subcortical stroke
• Age 40 yrs and older
• ≥ 6 months post ischemic stroke or ≥ 12 months post hemorrhagic stroke
• Residual arm hemiparesis as indicated by Fugl-Meyer Upper Extremity score between 20-65
• Having the ability to perform reaching movements with the paretic arm in standing without an assistive device.

Exclusion Criteria for stroke:

• Stroke involving bilateral hemisphere, brainstem or cerebellum
• Any medical condition precluding participation in testing
• Other health conditions affecting balance and upper extremity movement function beyond the effects of stroke.

Inclusion Criteria for healthy controls:

• Age-matched to the stroke subjects
• Without a history of stroke or any known neurological conditions
• Having the cognitive ability to follow two-step commands and give informed consent

Exclusion Criteria for healthy controls:

• Any medical condition precluding participation in testing
• Other health conditions affecting balance and upper extremity movement function beyond the effects of stroke.

Participants were also excluded if they did not meet the TMS safety criterion including having implantable medical devices, history of seizures, taking medications to reduce anxiety, sedatives, and seizure, and pregnancy.