Cerebrovascular disease is a major cause of disability worldwide. The catastrophic burden of stroke is more dramatic in low- and middle- income countries, and the scarcity of evidence-based rehabilitation interventions represents a major challenge to global health care. Upper limb weakness is frequent after stroke, but there is no universally accepted treatment to effectively improve hand function in patients with moderate and severe motor impairment. These are the patients in deepest need of rehabilitative interventions. This project addresses this important issue, by testing effects of a novel approach. The investigators will non-invasively stimulate peripheral nerves in order to enhance effects of motor training aided by an electrical stimulation device in patients with moderate to severe hand weakness. Our hypothesis is that peripheral nerve stimulation will enhance effects of motor training in patients in the chronic stage after stroke.

The objective of this protocol is to determine whether a neuromodulation intervention associated with functional electrical stimulation, when combined with task-specific training over several sessions, decreases upper limb motor disability, motor impairment, overall disability and improves quality of life compared to the sham intervention and functional electrical stimulation.

The interventions will consist of three sessions per week, over six weeks, of outpatient functional electrical stimulation of the paretic wrist and task-specific training. In each session, either active peripheral nerve stimulation (PNS) or sham PNS will be applied. Before the first session, patients will be familiarized with the procedures.

Inclusion Criteria:

• Age, 18 years or older;
• Ischemic or hemorrhagic stroke at least six months before, confirmed by computed tomography or magnetic resonance imaging;
• Moderate to severe motor impairment of an upper limb, defined as a score between 7 and 50 on the Fugl-Meyer Assessment of Sensorimotor Recovery after stroke, a scale with scores for upper limb ranging from 0 (no function) to 66 (normal function);
• Ability to provide written Informed Consent (patient or legal representative);
• Ability to comply with the schedule of interventions and evaluations in the protocol.

Exclusion Criteria:

• Lack of ability to voluntarily activate any active range of wrist extension;
• Anesthesia of the paretic hand;
• Severe spasticity at the paretic elbow, wrist, or fingers, defined as a score of >3 on the Modified Ashworth Spasticity Scale;
• Active joint deformity;
• Uncontrolled medical problems such as end-stage cancer or renal disease;
• Pregnancy;
• Seizures, if current use of drugs that may decrease seizure threshold such as tryciclic antidepressants;
• Pacemakers;
• Other neurological disorders such as Parkinson's disease;
• Psychiatric illness including severe depression;
• Aphasia or serious cognitive deficits that preclude comprehension of the experimental protocol or ability to provide consent;
• Treatment of upper limb spasticity with botulinum toxin within the past three months.
• Lesions that affect the cerebellum or cerebelar/vestibular pathways in the brainstem