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 …