Research scientists are unclear about the precise cause of migraine headaches. There seems to be general agreement, however, that a key element is blood flow changes in the brain. People who get migraine headaches appear to have blood vessels that overreact to various triggers.

    Scientists have devised one theory of migraine, which explains these blood flow changes, and also certain biochemical changes that may be involved in the headache process.

    According to this theory, the nervous system responds to a trigger such as stress by causing a spasm of the nerve-rich arteries at the base of the brain. The spasm constricts several arteries supplying blood to the brain, including the scalp artery and carotid or neck arteries.

    As these arteries constrict, the flow of blood to the brain is reduced. At the same time, blood-clotting particles called platelets clump together and dash, a process which is believed to release the neurotransmitter-Serotonin. Serotonin acts as a powerful constrictor of arteries, further reducing the blood supply to the brain.

    Reduced blood flow decreases the brain's supply of oxygen. Neurological Symptoms signaling a headache, such as distorted vision or speech, may then result similar to symptoms of stroke.

    Reacting to the reduced oxygen supply, certain arteries within the brain open wider to meet the brain's energy needs. This widening or dilation spreads, finally affecting the neck and scalp arteries. The dilation of these arteries triggers the release of pain- producing substances called prostaglandins from various tissues and blood cells.

    Chemicals that cause inflammation, swelling, and substances which increase sensitivity to pain are also released. The result according to this theory: a throbbing pain in the head.

    More recent neuro imaging techniques seem to show that migraine is primarily a disorder of the brain (neurological), not of the blood vessels (vascular). A spreading depolarization (electrical change)may begin 24 hours before the attack, with onset of the headache occurring at about the time of maximum brain coverage.

    The effects of migraine may persist for some days after the main headache has ended. Many sufferers report a sore feeling in the area where the migraine was, and some report impaired thinking for a few days after the headache has passed.

    In 2005,a research was made and published indicating that in some people with a patent foramen ovale(PFO), a hold between the upper chambers of the heart, migraine might result and that the occurrence of migraines might end if the hold were blocked.