What's Happening During a Migraine

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.

"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.