Migraine

When one hears migraine, one tends to think “terrible headache.” But a migraine is more than a headache; and in fact, head pain, a common component of migraine, is not a necessary component. A migraine is best thought of as an episodic intense heightening of sensation, especially in those sensory systems served by the cranial nerves. Generally, this results in severe head pain, but heightened sensitivity to light (photophobia), sound (phonophobia), odors (osmo-phobia), and touch to the skin (allodynia) occur too. This entry discusses the types of migraines, some of their physical symptoms, and migraine research.

Migraines have been described in literature and in medical writings since antiquity. The basic characteristics of migraine headache—its throbbing nature, the fact that it is usually more intense on one side of the head, and its association with nausea and often vomiting along with sensitivity to light, sound, and other sensory stimuli—led to its recognition as a distinct illness centuries ago. Extensive recent epidemiological work has demonstrated what a widespread health problem migraines are. In 2004, the World Health Organization identified the headache as one of the 20 leading causes of chronic disability worldwide.

Although many subtypes of migraine have been identified; however, two account for the preponderance of cases and also represent the forms of most interest in terms of perception. A migraine without aura is characterized predominantly by a severe headache meeting the earlier description. A migraine with aura involves a similar headache preceded or accompanied by transitory neurological symptoms referred to the aura. The aura typically begins 30 minutes to 1 hour before headache onset and lasts between 6 and 60 minutes. Auras may be experienced either as hallucinations (positive phenomena) or as functional loss (negative phenomena). The most common type of aura is visual (90% of auras). It is important to note, however, that somatosensory auras (experienced as tingling or numbness), olfactory auras (hallucinatory odors), and auras affecting speech, language reception, and other higher order cognitive functions also occur. Surprisingly very few individuals report auras in the auditory (hearing) modality; the [Page 553]reason for this is not at all clear. Migraine aura can also occur alone (migraine with aura without headache). This type of migraine is probably far more common than is recognized because the aura symptoms rarely persist longer than 30 minutes and are not followed by debilitating pain; people often don't report this to their physicians and don't realize that they are experiencing a form of migraine.

A visual migraine aura is a striking perceptual experience. Some auras involve only negative symptoms—the gradual loss of vision across one half of the visual field. So, for example, everything to the right of where one is looking disappears, whereas everything to the left remains intact. However, more common is a positive aura or an aura that combines positive and negative features. Although there are a number of variants of positive aura, the most common one—called a fortification aura because of its resemblance to medieval fortifications—is unmistakable. What begins as a tiny flashing spot of light just off the center of gaze gradually enlarges into a C-shaped arc of zigzag line elements. These lines are typically very bright and in constant roiling motion. Over a period of about 30 minutes, this zigzag pattern gradually spreads out into the periphery on one side, obliterating vision in that region. The hollow of the C is often a region of scotoma or blindness. One is not aware of the vision loss here because the human brain is very good at filling in, completing a missing hole with information “guessed” based on what surrounds it. However, if one takes a pencil and moves its tip into the center of the C, in many cases the tip of the pencil will vanish.

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