Explosive Synchronization of Brain Network Activity in Chronic Pain

Inclusion Criteria For Fibromyalgia Participants: * Satisfy the American College of Rheumatology (2011) survey criteria for the classification of Fibromyalgia (FM). * Continued presence of pain for more than 50% of days for the past month. * Mean recalled pain over the last seven days (7-day recall) greater than or equal to 3 on a 10 centimeter (cm) Visual Analog Scale (VAS) for pain; 7-day recall * Willing to limit the introduction of any new medications or treatment modalities for control of FM symptoms during the study. * Right-handed. * Able to travel to the study site to receive (HD-tDCS) treatments five times weekly * Understanding and willing to complete all study procedures. * Capable of giving written informed consent. Inclusion Criteria for Healthy Control Participants: * Right-handed * Pain less than 0.5cm on a 10cm Visual Analog Scale (VAS) for pain; 7-day recall * Understanding and willing to complete all study procedures * Capable of giving written informed consent Exclusion Criteria for Fibromyalgia Participants: * Presence of a concurrent autoimmune or inflammatory disease such as rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, et cetera (etc.) that causes pain. * History of head injury with substantial loss of consciousness * Peripheral neuropathy of known cause that interferes with activities of daily living. * Routine daily use of opioid analgesics, marijuana, or history of substance abuse. * Stimulant medications, such as those used to treat attention-deficit/hyperactivity disorder (ADHD)/Attention deficit disorder (ADD) (for example (e.g.), amphetamine/ dextroamphetamine \[Adderall®\], methylphenidate, dextroamphetamine), or the fatigue associated with sleep apnea or shift work (e.g., modafinil), are excluded. * Concurrent participation in other therapeutic trials. * Use of as needed (PRN) over the counter (OTC) pain medications (Nonsteroidal anti-inflammatory drugs (NSAIDs), etc.) on day of electroencephalogram (EEG)/Magnetic resonance imaging (MRI). * Use of PRN opioid analgesics 48 hours prior to EEG/MRI scan. * Pregnant or nursing. A pregnancy test will be given prior to EEG/MRI sessions. * Severe psychiatric illnesses (current schizophrenia, major depression with suicidal ideation, substance abuse within two years) * Contraindications to EEG/MRI or HD-tDCS methods. These may include but are not limited to: surgical clips, surgical staples, metal implants, and certain metallic dental material. * Any impairment, activity or situation that in the judgment of the Study Coordinator or Principal Investigators that would prevent satisfactory completion of the study protocol. This includes unreliable, or inconsistent pain scores as deemed by the principal investigator. * Sufficient knowledge of HD-tDCS techniques to prevent "blinding" of the patient to the study interventions (including significant previous tDCS or HD-tDCS treatment) * Presence of factors that may preclude the safe use of HD-tDCS * History vascular surgery in lower limbs or current lower limb vascular dysfunction. * Subjects with Worker's Compensation, Workman's Compensation, civil litigation or disability claims pertinent to the subject's fibromyalgia; current involvement in out-of-court settlements for claims pertinent to the subject's fibromyalgia; or currently receiving monetary compensation as a result of any of the above. * Inability or unwillingness of individual to give written informed consent. Exclusion Criteria for Healthy Control Participants: * Have met the American College of Rheumatology (2011) survey criteria for the classification of FM. * Have any chronic medical illness including psychiatric disorders (psychosis, schizophrenia, delusional disorder, etc). (self-reported) * History of head injury with substantial loss of consciousness * Peripheral neuropathy of known cause that interferes with activities of daily living * Routine daily use of opioid analgesics, marijuana or history of substance abuse * Stimulant medications, such as those used to treat ADD/ADHD (e.g., amphetamine/ dextroamphetamine \[Adderall®\], methylphenidate, dextroamphetamine), or the fatigue associated with sleep apnea or shift work (e.g., modafinil), are excluded. * Concurrent participation in other therapeutic trials. * Pregnant or nursing. A pregnancy test will be given prior to EEG/MRI sessions. * Contraindications for EEG or MRI. * Use of PRN over the counter (OTC) pain medications (NSAIDs, etc.) on day of MRI scan. * Use of PRN opioid analgesics 48 hours prior to MRI scan. * Active substance disorder in the past 24 months, as determined by subject self-report. * History vascular surgery in lower limbs or current lower limb vascular dysfunction. * Any impairment, activity or situation that in the judgment of the Study Coordinator or Principal Investigators that would prevent satisfactory completion of the study protocol. * Inability or unwillingness of individual to give written informed consent.