Optimized tDCS for Fibromyalgia: Targeting the Endogenous Pain Control System

This trial aims at understanding the mechanisms of optimized transcranial direct current stimulation (tDCS) (16 tDCS sessions combined with exercise)\] on pain control. Optimized tDCS can lead to stronger engagement of the endogenous pain regulatory system that will ultimately lead to increased pain relief in patients with fibromyalgia (FM). Therefore, the investigators designed a 2x2 factorial mechanistic trial \[tDCS (active and sham) and aerobic exercise (AE) (active and control)\] to evaluate the effects of 4 weeks of tDCS coupled with exercise on the endogenous pain regulatory system assessed by conditioned pain modulation (CPM) and central sensitization as assessed by temporal slow pain summation (TSPS), and compared to either intervention alone and to no intervention.

Recent evidence has suggested that FM pain can be related to deficits in pain endogenous regulatory control and that novel non-pharmacological interventions, such as tDCS can modulate this system and, consequently, reduce pain intensity. Widespread pain in FM is thought to represent enhanced pain sensitivity that is maintained by central mechanisms. This suggests changes in the descending pain control mechanisms and a possible relationship with the central sensitization phenomenon. Recent evidence has suggested that pain inhibitory pathways are affected in FM; thus, further understanding these pathways' role can significantly change how the treatment of this condition. In this study the investigators will test the effects of two interventions -tDCS and aerobic exercise - on the modulation of the endogenous inhibitory pain system in fibromyalgia.

Eligibility Criteria:
Inclusion Criteria:

1. Age range 18-65 years,
2. Diagnosis of FM pain according to the ACR 2010 criteria (existing pain for more than 6 months with an average of at least 4 on a 0-10 VAS scale) without other comorbid chronic pain diagnosis,
3. Pain resistant to common analgesics and medications for chronic pain such as Tylenol, Aspirin, Ibuprofen, Soma, Parafon Forte DCS, Zanaflex, and Codeine,
4. Must have the ability to feel sensation by Von-Frey fiber on the forearm,
5. Able to provide informed consent to participate in the study.

Exclusion Criteria:

1. Clinically significant or unstable medical or psychiatric disorder,
2. history of substance abuse within the past 6 months as self-reported (if subject reports a history of substance abuse, we will confirm using DSM V criteria),
3. Previous significant neurological history (e.g., traumatic brain injury), resulting in neurological deficits, such as cognitive or motor deficits, as self-reported,
4. Previous neurosurgical procedure with craniotomy,
5. Severe depression (If a patient scores \>30 on the Beck Depression Inventory, one will obtain clearance. If one does not pass the medical clearance, one will not be included in the study)
6. Pregnancy (as the safety of tDCS in pregnant population (and children) has not been assessed (though risk is non-significant), the investigators will exclude pregnant women (and children). Women of child-bearing potential will be required to take a urine pregnancy test during the screening process and at every week of stimulation),
7. Current opiate use in large doses (more than 30mg of oxycodone/hydrocodone or 7.5mg of hydromorphone (Dilaudid) or equivalent),
8. Patients will be excluded when they have increased risk for exercise