Functional MRI-BOLD of Visually Triggered Headache in Patients With Migraine

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Abstract
THE VISUAL aura of the migraine attack has been explained by the spreading depression (SD) of Leao, a neuroelectric event beginning in the occipital cortex and propagating into contiguous brain regions.1 This hypothesis was initially based on the stimulative followed by suppressive and slowly spreading clinical features of the aura,2,3 and later supported by cerebral blood flow (CBF) measurements of spreading hypoperfusion4,5 The early depolarizing or activation phase of experimental SD, however, is associated with a transient but pronounced CBF increase that precedes spreading hypoperfusion,6,7 presumably in response to the increased substrate demand of neurons attempting to repolarize. This has not been documented in patients except possibly in an early study when migraine attacks were triggered during intracarotid xenon-133 CBF measurements.4 To achieve information at this critical stage, we attempted to visually trigger migraine attacks in susceptible individuals. By using recently developed functional magnetic resonance imaging based on the blood oxygenation level-dependent (fMRI-BOLD) technique,8 we were able to measure, with millimeter resolution, second-to-second activation of occipital cortex to visual stimulation in these patients, and to observe suppression of neuronal activation before and during attacks. Our results also suggest that neuronal suppression is accompanied by hyperoxygenation of the occipital cortex during the early minute of the attack.

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