Discussion
hyperperfused, hypoperfusion, migraineurs’ perfusion differed from HC, headache, migraine, hyper-perfusion, hypo-perfused
MIGRAINE, HYPOPERFUSION, CORTEX
This study analysed interictal brain perfusion of episodic migraineurs. We found that their perfusion differed in several areas that did not respect the territories of specific blood vessels. Furthermore, tDCS of the occipital lobe altered perfusion compared with sham treatment. We discuss clinical findings in an earlier articlePrevious studies analysing brain perfusion in migraineurs with aura suggested hypoperfusion—or the co-occurrence of hypo- and hyperperfused areas—during the aura, followed by hyperperfusion during the headache phase that eventually normalisedIn our sample, we found both hypoperfusion (i.e., lower CBF in patients compared to HC) and hyperperfusion (see Tables A more detailed analysis of the areas affected by perfusion changes during the interictal period does not reveal a clear picture. Previous studies in episodic migraine patients indicated alterations in the right middle temporal gyrusMoreover, the functional connection between the areas with altered perfusion is unclear. Only one of the hypo-perfused areas harbours a large-scale network—the angular gyrus (see Table These discrepant findings are evocative of the discussion about structural changes in migraineurs detected by voxel-based morphometry that likewise are inconsistent among studies and therefore raise the question of their validity and implicationsComplicating matters further, only one area listed in Tables If cerebral perfusion correlates at least to some degree with cortical activityIn a previous paper, we analysed the effect of tDCS on monthly migraine days in the patients enrolled in this studyAt the first follow-up visit (F1), tDCS resulted in altered perfusion in frontal, temporal, and parietal cortices and the occipital pole. The hyper-perfusion in the occipital pole was expected, as anodal tDCS—which is in principle excitatory for the underlying cortex—generally induces hyper-perfusion in the stimulated area, including the cuneusThe only overlap of the areas of stimulation-induced alterations of perfusion and the areas in which migraineurs’ perfusion differed from HC was the right parietal operculum. Thus, our findings do not explain how stimulation led to the clinical effect. However, as we did not scan the participants when migraine frequency differed significantly between the two groups, we cannot tell whether the alterations in perfusion had propagated to other brain areas when the effect set in.At the second follow-up examination (F2), perfusion did not differ anymore between patients in the active and the sham tDCS groups. These findings suggest a slowly fading tDCS effect that may correlate with the reduction of the clinical effects.