Peri-ictal normalization of visual cortex excitability in migraine: an MEG study

To delineate if the change in cortical excitability persists across migraine attacks, visual evoked magnetic fields (VEF) were measured in patients with migraine without aura during the interictal (n = 26) or peri-ictal (n = 21) periods, and were compared with 30 healthy controls. The visual stimuli were checkerboard reversals with four different check sizes (15', 30', 60' and 120'). For each check size, five sequential blocks of 50 VEF responses were recorded to calculate the percentage change of the P100m amplitude in the second to the fifth blocks in comparison with the first block. At check size 120', interictal patients showed a larger amplitude increment than controls [28.1 +/- 38.3% (s.d.) vs. 8.7 +/- 21.3%] in the second block and a larger increment than peri-ictal patients in the second (28.1 +/- 38.3% vs. -3.2 +/- 19.2%), fourth (22.7 +/- 31.2% vs. -5.7 +/- 22.3%) and fifth (20.5 +/- 30.4% vs. -10.8 +/- 30.1%) blocks (P < 0.05). There was no significant difference at other check sizes or between peri-ictal patients and controls. In conclusion, there may be peri-ictal normalization of visual cortical excitability changes in migraine that is dependent on the spatial frequency of the stimuli and reflects a dynamic modulation of cortical activities.