The purpose of this study is to find out what are the best settings for applying electrical nerve stimulation over the skin for the short-term improvement of hand dysfunction after a stroke. The ultimate goal is to some day design an effective long-term training program to help someone recovery their ability to use their hands and function independently at home and in society. In order to know how to apply electrical nerve stimulation to produce a good long-term effect on hand dysfunction, the investigators first need to know how to make it work best in the short-term, and improve our understanding of for whom it works and how it works. The investigators will use a commercially available transcutaneous electrical nerve stimulation (TENS) unit to gently apply electrical nerve stimulation over the skin of the affected arm. This is a portable, safe and easy to use device designed for patients to operate in their homes.

Inclusion Criteria:

• Age 18-80 years, has residual hand motor dysfunction caused by a single ischemic and/or hemorrhagic stroke greater than 6 months prior to enrollment.

Exclusion Criteria:

• Pregnant; uncontrolled medical problems including but not limited to severe cardiovascular and cardiopulmonary disease; active cancer; significant hand joint deformity or other diagnosis with major effect on hand function besides stroke; severe alcohol or drug abuse within the past year; untreated or inadequately treated major depression; spasticity score >3 on the MAS; lack of finger range of motion of at least 10 degrees; severe aphasia or other communicative, behavioral or cognitive impairment that significantly interferes with the participant's ability to comply with the protocol or provide informed consent. In addition, patients will be excluded if they have a pacemaker.