Investigation and Modulation of the Central Mu-Opioid Mechanism in Migraine (in Vivo)

Inclusion Criteria:

* Male or female, aged 18 to 65 (inclusive)
* Patients must have Episodic migraines that started before the age of 50, and currently experience:

  * Chronic migraine (ICHD-3-beta), headache occurring on 15 days/month for more than six months, which, on at least eight days/month, has the features of a migraine headache.
  * Episodic migraine (low frequency), specifically those with headache occurring less than 8 days/month.
* Willing to limit the introduction of new treatments and medications during the study period.

Exclusion Criteria:

* Significantly greater pain in body sites other than the head
* Active, untreated major concurrent systemic illness other than migraine

  * Medical conditions that can impair health status independent of migraine (including cardiopulmonary disorders, malignancy, uncontrolled endocrine or allergies)
  * Systemic rheumatic disorders (i.e., rheumatoid arthritis, systemic lupus erythematosus, gout, and fibromyalgia);
* History or current evidence of a psychotic disorder (e.g., bipolar disorder, schizophrenia) or severe major depression, as evidenced by Beck Depression score of \>30\*
* History of neurological disorder (e.g., epilepsy, stroke, neuropathy, neuropathic pain)
* Medication overuse headache (ICHD-3), regular intake for ≥10 days per month of ergotamine, triptans, combination analgesics, or any combination thereof OR ≥15 days per month of simple analgesics (acetaminophen, aspirin, NSAID), for more than 3 months
* Current use of opioid or dopaminergic drugs (or use within the last 3 months) or substance abuse (self-reported)
* Drug test positive for opioid or recreational drug (e.g., cannabis) at the time of the PET scan visits
* Allergic response to study radiotracers or chemically related drugs
* Excluded by MRI Center or PET Center safety screening checklist (as administered by study staff)
* Pregnant or lactating (negative urine pregnancy test must be available before any PET procedures are initiated)
* Prior use of tDCS