There is increasing evidence that a center deep in the core of the brain causes production of migraine symptoms. This center or "migraine generator" may be activated by trigger factors from outside the body, such as bright light, odors and weather change, or from within the body by stressful circumstances, hormonal change and lack of sleep.
Nerve impulses from the migraine generator cause a release of chemical messengers (neurotransmitters) onto blood vessels and tissues in the head. This results in expansion and inflammation of blood vessels over the surface of the scalp and brain, causing the familiar throbbing pain of migraine headache.
The migraine generator affects other nearby areas in the brain, resulting in an increased sensitivity to light, sound, and smell. This may force the migraine sufferer into a quiet and dark environment in an attempt to avoid all stimuli. Also, the brain center for nausea and vomiting is stimulated, further aggravating the misery felt during a migraine event.
Individual sensitivity to migraine is determined by a number of factors, including genetics, gender, and reactivity to triggering factors. While each of us has a potential for migraine, it's development depends on many factors. A strong family history is often present, although the disorder may have differing severity in different members of the same family. Females are more commonly affected than males, particularly during childbearing years, when changing hormonal levels may have an important effect on the level of migraine activity.