There are two phases.

Phase I: A single visit which includes a screening, clinical scales, and a MRI scan with simultaneous tES/sham tES in a randomized block design. Enrolls both Cervical Dystonia (CD) patients and healthy controls.

Phase II: 5 consecutive days of 30-90 min visits to campus for tES or sham tES. Transcranial magnetic stimulation (TMS) measures and clinical scales will also be included on Day 1 and Day 5 visits. Enrolls only CD patients.

Phase I:

Enrolls both CD patients and healthy controls.

One approximately 3 hour visit which includes:

• a screening & neurological exam,
• clinical scales & questionnaires,
• a (approx.) 60 min MRI scan with simultaneous tES/sham tES in a randomized block design and EMG

Phase II:

Enrolls only CD patients.

Five consecutive days of study visits.

Day 1:

• TMS screening,
• repeated neurological assessment and clinical scales if >1 month since MRI visit
• 30 min TMS session with concurrent EMG
• 20 min tES or sham tES session

Days 2-4:

- 20 min tES or sham tES session

Day 5:

• 20 min tES or sham tES session
• 30 min TMS session with concurrent EMG
• repeated neurological assessment and clinical scales

Primary Cervical Dystonia

Inclusion Criteria:

• Right-handed
• On a stable dose of all medications used to treat dystonia for the month previous to enrollment
• No botox injections in the 10 weeks previous to enrollment

Exclusion Criteria:

• Any contraindication to MRI scanning, tES, or TMS (e.g pregnancy, history of seizures, significant systemic medical conditions, untreated psychiatric or neurological conditions)
• Evidence on neurological exam of any potentially confounding neurological disorder
• Evidence of significant cognitive impairment
• Patients with dystonia symptoms beginning prior to the age of 18 will be excluded
• Patients with secondary dystonia resulting from medications or that are part of another neurological disorder (e.g. Parkinson's disease) will be excluded
• Medication that might predispose the subject to seizures

Healthy Controls

Inclusion Criteria:

- Right-handed

Exclusion Criteria:

• Any contraindication to MRI scanning, tES, or TMS (e.g pregnancy, history of seizures, significant systemic medical conditions, untreated psychiatric or neurological conditions)
• Evidence on neurological exam of any potentially confounding neurological disorder
• Evidence of significant cognitive impairment
• Medication that might predispose the subject to seizures