Patients who report that exposure to bright light or strenuous physical activity will induce migraine aura will be provoked using one or both of these methods. Followingly the patients will be examined by functional MRI. Íf the patients develop migraine headache, MR angiography will be performed as well. The primary study hypothesis is that the functional MRI signal will show features similar to those of the electrophysiological phenomenon of cortical spreading depression.