It is to be expected that differences in electrical activity of the brain between migraine patients with aura and those without aura can only be revealed by stimuli that provoke visual spatial processing, i.e. stimuli that trigger so called endogenous Visual Evoked Potential (VEP) activity. This is not the case for the flashes and checkerboard reversals. Those stimuli elicited exogenous activity only. During and between attacks the blood flow of migraineurs with aura changes in the posterior cerebral part of the brain, which is assumed to be specialized in the processing of spatial aspects of visual stimuli.
Reaction times (RTs), early and late Event Related Potential (ERP) differences were compared at 12 scalp positions for two groups of migraineurs (with and without aura) and a control group. They had to perform a passive attention task, checkerboard reversals, and an active attention task, where attention was either divided into or focussed at spatial locations.
In agreement with many studies on migraine, checkerboard stimuli did not differ on any early components. However, RTs were faster for migraineurs with aura and their early components were different when stimuli were highly attended. This is probably because these stimuli can relatively easily trigger cortical activity due to an over activated central mechanism and an enhanced level of attention.