Spatio-temporal imaging of cortical desynchronization in migraine visual aura: a magnetoencephalography case study.

OBJECTIVE To determine cortical oscillatory changes involved in migraine visual aura using magnetoencephalography (MEG). BACKGROUND Visual aura in the form of scintillating scotoma precedes migraine in many cases. The involvement of cortical spreading depression within striate and extra-striate cortical areas is implicated in the generation of the disturbance, but the details of its progression, the effects on cortical oscillations, and the mechanisms of aura generation are unclear. METHODS We used MEG to directly image changes in cortical oscillatory power during an episode of scintillating scotoma in a patient who experiences aura without subsequent migraine headache. Using the synthetic aperture magnetometry method of MEG source imaging, focal changes in cortical oscillatory power were observed over a 20-minute period and visualized in coregistration with the patient's magnetic resonance image. RESULTS Alpha band desynchronization in both the left extra-striate and temporal cortex persisted for the duration of reported visual disturbance, terminating abruptly upon disappearance of scintillations. Gamma frequency desynchronization in the left temporal lobe continued for 8 to 10 minutes following the reported end of aura. CONCLUSIONS Observations implicate the extra-striate and temporal cortex in migraine visual aura and suggest involvement of alpha desynchronization in generation of phosphenes and gamma desynchronization in sustained inhibition of visual function.