Mechanisms of migraine aura revealed by functional MRI in human visual cortex

Cortical spreading depression (CSD) has been suggested to underlie migraine Visual aura. However, it has been challenging to test this hypothesis in h uman cerebral cortex. Using high-field functional MRI with near-continuous recording during visual aura in three subjects, we observed blood oxygenati on level-dependent (BOLD) signal changes that demonstrated at least eight c haracteristics of CSD, time-locked to percept/onset of the aura. initially, a focal increase in BOLD signal (possibly reflecting vasodilation), develo ped within extrastriate cortex (area V3A). This BOLD change progressed cont iguously and slowly (3.5 +/- 1.1 mm/min) over occipital cortex, congruent w ith the retinotopy of the visual percept. Following the same retinotopic pr ogression, the BOLD signal then diminished (possibly reflecting vasoconstri ction after the initial vasodilation), as did the BOLD response to visual a ctivation. During periods with no visual stimulation, but while the subject was experiencing scintillations, BOLD signal followed the retinotopic prog ression of the Visual percept. These data strongly suggest that an electrop hysiological event such as CSD generates the aura in human visual cortex.