Animation of cortical spreading depression Migraine is believed to be primarily a neurological disorder, while others believe it to be a neurovascular disorder with blood vessels playing the key role, although current evidence does not support this completely. Others believe both are likely important. One theory is related to increased excitability of the cerebral cortex and abnormal control of pain neurons in the trigeminal nucleus of the brainstem. Aura Cortical spreading depression, or spreading depression according to Leão, is a burst of neuronal activity followed by a period of inactivity, which is seen in those with migraines with aura. There are a number of explanations for its occurrence, including activation of NMDA receptors leading to calcium entering the cell. After the burst of activity, the blood flow to the cerebral cortex in the area affected is decreased for two to six hours. It is believed that when depolarization travels down the underside of the brain, nerves that sense pain in the head and neck are triggered. Pain The exact mechanism of the head pain which occurs during a migraine episode is unknown. Some evidence supports a primary role for central nervous system structures (such as the brainstem and diencephalon), while other data support the role of peripheral activation (such as via the sensory nerves that surround blood vessels of the head and neck). The potential candidate vessels include dural arteries, pial arteries and extracranial arteries such as those of the scalp. The role of vasodilatation of the extracranial arteries, in particular, is believed to be significant. Neuromodulators Adenosine, a neuromodulator, may be involved. Released after the progressive cleavage of adenosine triphosphate (ATP), adenosine acts on adenosine receptors to put the body and brain in a low activity state by dilating blood vessels and slowing the heart rate, such as before and during the early stages of sleep. Adenosine levels have been found to be high during migraine attacks. Caffeine's role as an inhibitor of adenosine may explain its effect in reducing migraine. Low levels of the neurotransmitter serotonin, also known as 5-hydroxytryptamine (5-HT), are also believed to be involved. Calcitonin gene related peptides (CGRPs) have been found to play a role in the pathogenesis of the pain associated with migraine, as levels of it become elevated during an attack.
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