The main components of a ‘reward system’, and how it connects to brain areas involved in motivation and emotion, are now defined, and much has been discovered about the chemical messenger systems such as dopamine and noradrenaline that are fundamental to the mechanism of addiction.

Link to Addictions Hub

Initial Overview based on Wikipedia entry Jan. 5, 2016

The exact mechanisms of migraine are not known. It is, however, believed to be a neurovascular disorder. The primary theory is related to increased excitability of the cerebral cortex and abnormal control of pain neurons in the trigeminal nucleus of the brainstem.

The brains of fibromyalgia patients show functional and structural differences from those of healthy individuals, but it is unclear whether the brain anomalies cause fibromyalgia symptoms or are the product of an unknown underlying common cause.