The purpose of this study is to examine if the strong hand can assist in the recovery of muscle function in the weak hand after a stroke.

Hemiparesis is the most common motor impairment after stroke. Persistent deficits in the distal upper extremity lead to impaired hand function and disability in Activities of Daily Living, accruing enormous costs in terms of health care services and lost productivity. The mechanisms of recovery of hand motor function after stroke are poorly understood, and the protocols used in clinical practice lack a solid scientific rationale. Prior work has shown that grasping with the non-involved hand may assist in planning of grasp with the involved hand after stroke. The goal of the proposed project is to investigate the type and nature of information relayed across the hemispheres by prior manipulation with the non-involved hand to improve planning and control of grasp with the involved hand. Psychophysical methods using a grip instrument will be used to examine the type of information necessary for planning of grasp, and quantitative surface electromyography will be used to investigate the contribution of improved planning to neuromuscular control of grasp. Integration of these methods in the study of grasp control will clarify the neural mechanisms underlying hand dysfunction, and facilitate the development of rational therapeutic protocols for upper extremity rehabilitation after stroke.

Inclusion Criteria:

1. Previously right-handed subjects with hemiparesis and complaints of unilateral hand dysfunction during grasping resulting from a single unilateral cerebral infarct in the MCA territory affecting either the right or the left side of the brain at least 3 months prior to data collection
2. Previously right-handed healthy control subjects age-matched to the stroke patients
3. All subjects must have the ability to reach, grasp and lift the test object with both extremities (stroke patients with the impaired extremity as well) and complete the experimental protocol as assessed by the PI.
4. All subjects must score > 24 on the Folstein's mini-mental exam to screen out significant cognitive dysfunction
5. Subjects must obtain MRI or CT scan images of their brain taken since their stroke, or be willing to have a structural MRI or CT scan taken as part of this research study.

Exclusion Criteria:

1. Presence of clinically significant visual deficits, aphasia, neglect, or apraxia as determined by clinical neurologic examination that may interfere with the research protocol
2. Presence of sensory deficits in control subjects and in the non-involved hand of stroke subjects on testing of two-point discrimination
3. History of surgery or other significant injury to the upper extremities
4. Botulinum toxin injections in the upper extremity musculature in the three months prior to enrollment in the study.
5. Current treatment with intrathecal baclofen
6. Previous neurological illness such as head trauma, prior stroke, epilepsy, demyelinating disease
7. Complicating medical problems such as uncontrolled, diabetes with polyneuropathy, severe renal, cardiac or pulmonary disease, or any other severe concurrent medical problem that will interfere with obtaining reliable results.

Subjects with stroke will be recruited from the inpatient and outpatient Rehabilitation units at the Mount Sinai Medical Center and from referrals by community rehabilitation physicians and neurologists. Control subjects will be recruited by public advertisement in the New York City area. There are no exclusions based on gender or ethnic groups.