WASHINGTON (AP) - The pain of a migraine can be so intense it's disabling. Your head pulses, usually on one side, for hours or even days. Moving worsens the throbbing. You're nauseated, sensitive to light and sound. Sometimes you have an "aura," seeing pinpoints of light or other visual disturbances before the headache hits.

Many of those who suffer this pain don't realize that migraines - and not some other headache - are to blame, and millions go without treatment.

That's particularly disturbing to experts because, in a revolutionary shift, scientists are discovering that migraines are caused not by the abnormal blood vessels once blamed but by a unique electrical disorder of brain cells.

The findings open new avenues to attack these tenacious headaches, and suggest treating migraines is important because people who suffer very frequent attacks seem vulnerable to physical changes inside the brain that could lead to chronic pain.

"We should probably be treating very quickly," Dr. K. Michael Welch of the University of Kansas Medical Center in Kansas City, whose neurological research is spurring this new view of migraines, told a recent meeting at the National Institutes of Health.

One-fifth of sufferers are candidates for medicines that can cut frequent attacks by half, yet fewer than 1 million get preventive therapy, said Dr. Richard Lipton of New York's Albert Einstein College of Medicine. Once a migraine hits, only a fraction use the most powerful prescription treatments.

Why? Too many primary care physicians don't know how to treat migraines, specialists say.

At a recent seminar, only 45 percent of family physicians shown migraine symptoms got the diagnosis right. Plus, only one-third of patients have that classic aura before an attack - yet many doctors erroneously think no aura means no migraine, Lipton said.

Scientists once thought migraines were caused by abnormally dilated blood vessels. Hence, many pain relievers work by constricting blood vessels.

But new imaging devices allow scientists to watch patients' brains during a migraine attack, and they're discovering sufferers have abnormally excitable neurons, or brain nerve cells.

When something triggers a migraine, those neurons suddenly fire off electrical pulses at the back of the brain, firings that ripple across the brain's top and then back down to the brainstem, where important pain centers are located, Welch explains. This electrical "wave" spreads like water ripples when you throw a pebble in a lake.

In minutes, blood flow jumps, until the wave passes and blood flow sharply drops.

The resulting pain comes from either the brainstem activation or blood vessels inflamed by the rapidly changing blood flow - or both.

Experiments in which scientists use a powerful magnet to stimulate neurons provide startling evidence that some people's brains are predisposed to hyperexcitability. When people prone to migraines were stimulated, they literally saw spots similar to a migraine's aura. One even went into a migraine as spellbound scientists watched. But when people who don't get migraines were stimulated, their neurons weren't affected.

In real life what triggers these neurons? Too much or too little sleep, hunger, bright lights, certain foods, women's fluctuating estrogen levels.

Adding to the push for treatment, very frequent migraine attacks seem to physically change the brainstem's pain centers, sometimes leading to constant headaches, Welch says.

While scientists use the findings to hunt better treatments, helpful medicines are already available.

Most notably, some drugs that fight epilepsy by suppressing abnormal neuron firings - Depakote and gabapentin - also prevent migraines, says Dr. Stephen Silberstein of Thomas Jefferson University Hospital in Philadelphia. The four most powerful prescription treatments, called "triptans," shrink inflamed blood vessels. And women often are helped by adjusting birth control or hormone therapy to stabilize estrogen levels.

The treatments aren't perfect. But too many patients never see a doctor, or see one who follows the outdated practice of trying less powerful drugs first, Lipton says. His advice: Don't give up - if one drug doesn't help, demand another.

Copyright 2000 The Associated Press. All rights reserved.