Visual cortex hyperexcitability in migraine in response to sound-induced flash illusions

Sound-induced flash illusions depend on visual cortical excitability. In this study, we explored whether sound-induced flash illusions are perceived differently in migraine, a condition associated with pathologic cortical hyperexcitability. Methods: Sound-induced flash illusions were examined in 59 migraine patients (mean age 32 ± 16 years; 36 females), 32 without aura and 27 with aura, and in 24 healthy controls (mean age 42 ± 17 years; 16 females). Patients were studied during attacks and interictally. Visual stimuli (flashes) accompanied by sounds (beeps) were presented in different combinations: a single flash with multiple beeps was given to induce the perception of multiple flashes ("fission" illusion), and multiple flashes with a single beep were used to reduce the number of perceived flashes ("fusion" illusion). Results: For migraineurs, the fission illusion was reduced, especially during the attack, and almost abolished when a single flash was combined with 2 beeps (except for those without aura tested interictally); the fusion illusion was less consistently reported in both migraine groups, but not completely disrupted. Conclusions: Results from this study add novel clues to our understanding of visual cortex hyperexcitability in migraine, especially migraine with aura. Furthermore, these analyses underscore how pathologic changes in cortical excitability affect multisensory interactions. Cross-modal illusions represent a valid tool for exploration of functional connectivity between sensory areas, which likely has an important role in the pathophysiology of migraine.