What is the cause of migraine?
Cause...
There seems to be
general agreement 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 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
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 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.
More recent neuroimaging 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, research was published
indicating that in some people with a
patent foramen ovale (PFO), a hole
between the upper chambers of the
heart, migraine might result and that
the occurrence of migraines might end
if the hole were blocked. Several
clinical trials are currently under way
in an effort to determine if a causal
link between PFO and migraine can be
found. Early speculation as to this
relationship has centered on the idea
that the lungs detoxify blood as it
passes through. The PFO allows blood to
go directly from the right side of the
heart to the left without passing
through the lungs.