Carolyn Bernstein was sitting in a lecture hall one day during her second year at Boston University Medical School when her head began to pound and throb. She became dizzy and disoriented and felt so weak she thought she would faint. Bernstein managed to leave class and get home, where she collapsed into bed. She was suffering from her first migraine and she soon found out that there was no easy treatment. Bernstein says migraineurs—people who get migraines—are too often treated with condescension by doctors who tell them to "just deal with it."

Her experience led her to specialize in migraines. In addition to being on the faculty at Harvard Medical School, she also runs the Women's Headache Center in Cambridge, Mass. Unfortunately, such centers are rare and most migraineurs still struggle to find help. Bernstein says that's why she wrote her new book, "The Migraine Brain" (Free Press, 2008). Each migraineur's experiences are unique, Bernstein says. Some have attacks that last only a few hours; others can be in pain for days. Women are more likely to get migraines than men, for reasons doctors still don't fully understand. Migraines can't be cured, only treated with a range of medication and lifestyle changes. "I want to encourage people to seek help and not feel alone," Bernstein says. We asked Bernstein for a quick rundown on the science of migraines. Excerpts:

What is a migraine and why isn't it a headache?
Carolyn Bernstein: A migraine is actually part of an entire disease process and a headache is basically just pain in your head. Migraines are a constellation of symptoms that can include head pain but often times will include other symptoms as well, like nausea and vomiting. They can include changes in vision and abdominal pain. Some of the more-complex migraines can actually cause people to look like they are having a stroke. They are weak on one side or the other, and they have sensory changes. It's not nearly as clear-cut and straightforward as a headache, and it implies that something else is going on in the nervous system.

Is there any one symptom that defines a migraine?
There are many, many different kinds of described migraines. In order to make the diagnosis, you have to meet a certain diagnostic criteria, based on the number of headaches that you've had. If you've just had one headache with nausea and vomiting and some visual changes, you couldn't technically call that a migraine. You need to have had at least two. For kids, it has to be four or more.

Migraines don't always include the headache. There are some kinds of migraines, called migraine equivalents, where people will just have the visual symptoms, sometimes called the aura, but they will not have pain. Those can be hard to diagnose.
The question in the back of people's minds when they start to get one of these—and they are so dramatic and so extreme compared to a tension headache—is "Am I having a stroke? Do I have a tumor? Do I have an aneurysm that's bleeding in my brain?" The initial attack that you have is the one that you need to get checked out.

Would you advise someone who's had just one attack like this to tell her doctor about it? 
Absolutely. You want to get a diagnosis. It can be really helpful in treatment. There are certain kinds of medication for other conditions that you shouldn't take. For women in particular, certain kinds of migraines are actually associated with an increased risk of stroke if you are taking birth control pills.