Pathophysiology
The vascular hypothesis was an early theory that described
migraine aura as being caused by intracerebral vasoconstriction
followed by extracranial vasodilation.2 More recently, there have been
regional blood flow studies that do not support this hypothesis. The
currently accepted theory is that migraines are caused by neuronal
dysfunction. This dysfunction is caused by a wave of depressed
electrical activity that advances across the brain cortex at a rate
consistent with the spread of aura symptoms.
The pain associated with migraines is believed to originate in the
trigeminovascular system.2 This system provides a pathway in which
pain from the meningeal blood vessels can be transmitted to higher
centers within the central nervous system (CNS). This system also
innervates the pain-sensitive intracranial extracerebral blood vessels,
dura mater, and large venous sinuses.
When the nerves in the trigeminal system are activated, they
release various neuropeptides including calcitonin gene-related
peptide, neurokinin A, and substance P.2 These neuropeptides
cause vasodilation, which results in dural plasma extravasation
and ultimately neurogenic inflammation. This process causes pain
impulses to be transmitted to higher cortical pain centers, which
allows the migraine to be perceived.
This system may also be regulated in part by serotonin.2 If there
is a dysfunction in the calcium channels responsible for mediating
serotonin and excitatory neurotransmitter release, then a migraine
may result. This dysregulation of serotonin can cause vasodilation of
intracranial extracerebral blood