Why do some people suffer from the agonizing head pain of migraines—and the nausea and sensitivity to light that can accompany them—while others don't? The answer, at the biochemical level, is complicated, but probably boils down to this: Migraine sufferers' brains are simply more sensitive to outside stimuli than are other people's brains.

Migraines used to be blamed on blood vessels in the brain dilating, or opening up. The newer thinking is that the expansion of blood vessels is the result of some other event, not the cause. The cause may in part be the excitation of a nerve responsible for sensation in the face.

"It's called the trigeminal nerve," explains Larry Newman, MD, director of the Headache Institute at St. Luke's-Roosevelt Hospital Center in New York City.

When the trigeminal nerve is stimulated, it causes the release of a variety of neurotransmitters (among them serotonin, which is also associated with mood change). These in turn cause the blood vessels that surround the brain to expand and inflame.

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"Those blood vessels are attached to nerve fibers which transmit the pulsations from the blood vessels back into the brain, where you then perceive it as pain," says Dr. Newman.

"This is a system that we all have," says Michael Cutrer, MD, a neurologist at the Mayo Clinic in Rochester, Minn. "But in people who have migraine, it is a system vulnerable to being repeatedly activated when there's no good reason. Like a car alarm going off too often, instead of being a protective mechanism like it was built to be, it becomes a system that begins to interfere with your ability to function normally in your life."

Although some people experience a pre-attack aura, a typical migraine occurs in two steps.

Next Page: The trigeminal nerve is activated [ pagebreak ]

  • The trigeminal nerve is activated
    When the trigeminal nerve gets excited the most common first symptom is pain around the eye and temple. If that pain is treated quickly with migraine medications like triptans, inflammation can be reduced, and a sufferer can shut down the migraine relatively quickly. (Triptans act as an extra supply of serotonin to help narrow the blood vessels and block the transmission of pain to the nerves).
  • The central nervous system is triggered
    Left untreated another mechanism will trigger in the central nervous system itself. At this point that pain mechanism becomes very difficult to turn off. Medications at this stage are less likely to work. It's as if the pain has become independent of the original source at the trigeminal nerve.

A recipe for prolonged suffering
"Once it goes beyond a certain point, cutting off the source is no longer sufficient because the pain of the headache reverberates in the central nervous system," says Dr. Cutrer. "A different set of neurons has now become irritable and activated—and getting them back to normalcy is not easy. They can continue to be reactivated and reactivated and the headache becomes harder to treat."

That's the dreaded migraine phase that can go on for hours or days.

At that point, everything in your head can hurt: you can't wear earrings, you have to take off your glasses, you don't want to lie that side of your head on the pillow. Yes, even your hair hurts.

Because of the importance of catching migraines in the early phase, doctors advise patients to monitor triggers and symptoms to prevent excitation of the trigeminal nerve and, if that fails, to get the jump on treatment to calm it down. Triggers missed and medication delayed are a recipe for prolonged suffering.