O047. the Sound-Induced Flash Illusions Reveal Visual Cortex Hyperexcitability in Cluster Headache

Objectives Pathophysiology of cluster headache (CH) is not wellknown. Although posterior hypothalamus has been suggested to play a pivotal role, evidence exists of a more diffuse involvement of the central nervous system including brainstem and cerebral cortex. In this regard, we recently observed increased motor cortical excitability in episodic CH patients both outside and inside bout [1]. The sound-induced flash illusions (SIFI) represent an example of multisensory integration, and provide a tool to indirectly explore the excitability state of the visual cortex [2]. SIFI are classified as “fission” and “fusion” illusions. When one visual stimulus (flash) is accompanied by two or more auditory stimuli (beeps), it is often perceived as multiple flashes (fission illusion). Conversely, fusion illusion occurs when subjects perceive less number of flashes when these are presented with only one beep. On such bases, here we used SIFI to explore excitability of visual cortex in CH patients.