The purpose of this study is to investigate the mean number of stimulation (high definition-transcranial direct current stimulation) sessions (up to 26) needed to achieve a clinical response with this response defined as a 50% decrease in Visual Analog Scale (VAS) for pain. These data will be important in defining the optimal number of sessions for future fibromyalgia subjects in Phase III trials.

Inclusion Criteria:

• Providing informed consent to participate in the study
• 18 to 85 years old, both male and female
• Have a diagnosis of Fibromyalgia
• Existing pain for more than 3 months with an average of at least 4 on a 0-10 VAS scale
• Pain resistant to common analgesics and medications for chronic pain such as Tylenol, Aspirin, Ibuprofen, Soma, Parafon Forte DCS, Zanaflex and Codeine.

Exclusion Criteria:

• Pregnancy
• Contraindications to tDCS: metal in the head or implanted brain medical devices
• History of alcohol or drug abuse within the past 6 months as self-reported
• Use of carbamazepine within the past 6 months as self-reported
• Severe depression (with a score of >30 in the Beck Depression Inventory)
• Any history of epilepsy, stroke, moderate-to-severe traumatic brain injury or severe migraines
• History of unexplained fainting spells as self-reported
• Neurosurgery as self-reported