PLoS Medicine | www.plosmedicine.org 0001 Perspectives

Migraine is an episodic brain disorder [1] that affects about 15 percent of the population [2,3]. The disorder can be highly disabling [4], and has been estimated to be the most costly neurological disorder in the European Community, costing more than 27 billion per year [5]. Two clinical forms are commonly seen: migraine with aura and migraine without aura [6]. Aura in this context is defi ned as a recurrent disorder manifesting in attacks of reversible focal neurological symptoms, usually developing gradually over a period of fi ve to 20 minutes and lasting for less than 60 minutes. These symptoms are typically visual [7], and are often described as bright jagged lines (fortifi cation spectra) that move across the visual fi eld, often followed by visual loss (scotoma). The phenomenon of migraine has been known since antiquity. Now there are new data on anatomical alterations in the visual motion-processing regions. Do these new data shed light on aura, or perhaps illuminate more basic principles about the migrainous brain? Is the traditional view—that the migrainous brain is structurally normal—incorrect