 Healthy volunteers and patients with thromboembolic non-hemorrhagic hemispheric lesions at least 6 months after the stroke, aged 18 to 80 years. Patients who initially had a severe motor paresis below MRC grade 2, which subsequently recovered to the point that they have a residual motor deficit but can perform the required tasks, and those in whom isolated thumb movements can be evoked by TMS. Handedness will be assessed by the Edinburgh inventory scale. Subjects should be able to sustain attention to the task over 30 minutes. 