Cyclic changes of visual cortical excitability across migraine phases: A study with sound induced flash illusions

Abstract

Background and aims Abnormal cortical excitability has a role in migraine but the link with beginning and stop of migraine attacks remains unclear. Critical insight could come by excitability changes across the migraine cycle. Here we explore it through sound induced flash illusions (SIFI). SIFI are cross-modal illusory percepts critically dependent on visual cortical excitability (less illusions = increased excitability) that have been found to be altered in episodic and chronic migraine(1–2). Methods We performed SIFI on 108 patients with episodic migraine without aura (mean age 38; 60 females) and 24 healthy controls. Patients were studied across migraine cycle: 24 during the postictal phase, 20 ictal, 20 interictal, 20 preictal. SIFI were performed presenting a single flash accompanied by multiple beeps to evoke a “fission” illusion (see multiple flashes), and multiple flashes accompanied by a single beep to evoke a “fusion” illusion (less flashes seen). Results We found a significant decrease of the number of fission illusions during the preictal phase compared to the interictal one (p b .03) and during the postictal phase compared to the interictal one (p b .01). Furthermore, fission illusions were reduced in patients observed interictally than in controls (p b .01). As reduced illusions mean increased excitability, excitability, that interictally is greater than controls, increases further in preictal phase, reaches a maximum during attack, and then decreases till to the lowest interictally. Conclusions The study shows a “cortical excitability” cycle, close to the clinical migraine cycle, supporting the idea that increasing cortical excitability could be well at the basis of both attacks susceptibility and precipitation in migraine disease.