During the migraine-aura cerebral blood flow (CBF) is reduced in areas corresponding to the neurological deficits and symptoms. Whether this CBF reduction is the primary cause of the neurological deficits (the vascular theory) or a secondary result of primary neuronal dysfunction in particular "spreading depression" (SD) (the neurogenic theory) is still under discussion. The latter theory is supported by CBF investigations performed during attacks of migraine with aura (MA). The CBF reduction was found to be modest (20-35%) and not sufficient to cause ischemia which usually demands reduction of CBF by more than 50%. In addition the low-flow area appeared to "spreading" in the same manner as that seen in SD in the rat ("spreading oligemia"). Recent studies indicate, however, that the CBF reduction in most cases, after all, is sufficient to cause ischemia and that "spreading oligemia" might be an artifact caused by "scattered radiation". Persistent neurological deficits, EEG abnormalities and infarcts on CT-scans are seen after MA, thus further supporting the theory of vascular dysfunction (vasospasm) and ischemia as the cause of the migraine-aura.