First, let's define a few terms. Doctors divide headaches into two broad categories: those that are self-contained (primary headaches) and those that result from another illness or accident (secondary headaches). The best treatment for a secondary headache depends on its origin. For example, an antibiotic may be prescribed for a headache caused by a bacterial infection.

The most common type of primary headache is the familiar tension headache, which is usually stress related. (Doctors now label it a tension-type headache to counter the idea that knotted muscles are the principal cause.) In most cases, a couple of aspirin and a good night's sleep are all that's required to get rid of one.

Not so the mercifully uncommon cluster headache, so named because an attack typically repeats itself, often daily, with each episode lasting anywhere from an hour to an hour and a half. Cluster headaches usually strike their victims, generally men, at fixed times of the year. The pain is so searing that they are also known as suicide headaches. Immediate treatment with oxygen and migraine drugs given intravenously can sometimes provide relief.

Somewhere between tension and cluster headaches are migraines. Typically, the pain from a migraine is a throbbing one, restricted to one side of the head, that gets worse with movement and lasts from four hours to three days. Migraines are usually accompanied by either nausea and vomiting, as they were for TV producer Schipper, or extreme sensitivity to both light and sound. By contrast, patients suffering from tension-type headaches may react badly to either light or sound but not both.

It is a mistake, however, to stick too rigidly to these definitions. "At one time people thought that migraine was a disorder all its own and that tension-type headache was totally separate," says Dr. Ninan Mathew, director of the Houston Headache Clinic. "Now we realize that headaches are not that clear cut." Indeed, Mathew says, nearly any recurring headache that is debilitating enough to keep you away from work or the things you enjoy is probably a migraine.

	Three times as many women as men suffer from migraines. Men are five times as likely to have cluster headaches

As far back as the 1600s, the prominent English physician Thomas Willis suggested that headaches are caused by a rapid increase in the flow of blood to the brain. He theorized that the suddenly bulging blood vessels put pressure on nearby nerves and that these in turn trigger the pain. A variation on Willis' idea became the favored explanation for the cause of migraines. (An important network of blood vessels at the base of the brain bears Willis' name.)

Two things have occurred in the past couple of decades to alter that view. First, several imaging techniques were developed that allowed doctors to study blood flow in the living brain. Second, scientists learned a great deal more about the nerve endings that are embedded in the dura mater, the fibrous outer covering of the brain. Armed with these tools and that information, researchers concluded that the order of events in a migraine is not as straightforward as they had been taught. The nerve endings in the dura mater appear to act first, releasing proteins that cause the blood vessels to open and prime the nerves to maintain a state of alert. In other words, swollen blood vessels are the result of a growing migraine, not its cause.

Tracing the pathway of the affected nerve endings deeper into the brain led researchers to the trigeminal nerve, a complex network of nerve fibers that ferries sensory signals from the face, jaws and top of the forehead to the brain. During the course of a migraine, scientists discovered, the trigeminal nerve practically floods the brain with pain signals. The more researchers learn about the trigeminal nerve, the more they believe that it is involved in all types of primary headaches, including tension and cluster headaches. The differences in the headache types seem to stem from what activates the trigeminal nerve and how it responds.

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