The migraine process. 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 closes down or
constricts several arteries supplying blood to the
brain, including the scalp artery and the 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-a process which is believed to release a
chemical called 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. 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 which cause inflammation and swelling, and
substances which increase sensitivity to pain, are
also released. The circulation of these chemicals
and the dilation of the scalp arteries stimulate the
pain-sensitive nociceptors. The result, according to
this theory: a throbbing pain in the head.
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