excitability, the phosphene threshold (PT), a representative of visual
cortex excitability induced by transcranial magnetic stimulation
(TMS), was analyzed. PT is defined as the lowest intensity of a TMS
pulse required to evoke phosphenes [12]. Studies using TMS have
found significantly lower PT and a much higher proportion to evoke
phosphenes in migraineurs compared with healthy volunteers, which
benefits the cortical hyperexcitability theory [4,13]. Other studies have
achieved the opposite result [6,8] pointing out to decreased interictal
cortical excitability in migraineurs. To modulate the abnormal interictal
excitability in migraine patients, transcranial direct current stimulation
(tDCS) was applied. TDCS results in motor cortical excitability changes
in humans that occur during the application of direct current and
remain stable for up to 1 h after stimulation. Anodal tDCS increases
excitability, while cathodal tDCS decreases it [14–16]. Some studies
have demonstrated the effectiveness of using anodal [3] and cathodal
tDCS [9] for migraine treatment.