Objective: To describe the underlying dynamical mechanisms of photosensitive epilepsy (PSE) and different photosensitivity types. Methods: This retrospective study included healthy controls (HC), non-PSE patients with epilepsy (PWE), and PSE patients. All participants were stimulated with flickering white light (1-60Hz) under 10-20 EEG monitoring. Results: We observed significantly higher occipital Photoparoxysmal response (PPR) power in PSE patients compared to HC for stimulation frequencies 10Hz-20Hz. This activity was highest in Type 4, which shows a type-specific variation of the PPR. However, the excitability of the visual cortex, investigated by the occipital transient (P100) and steady-state visual evoked potentials (ssVEP), remained unchanged in most PSE types compared to HC and to PWE. The ssVEP power only increased significantly in Type 4 compared to HC. Instead, PSE patients showed apparent differences in functional connectivity in the PPR band (3-4Hz) with hypoconnected centro-parietal regions and hyperconnected anterior and anterio-posterior areas compared to HC and PWE for stimulation frequencies 10Hz-20Hz. Conclusion: PSE is a network effect modulated by hyperconnected anterior and anterio-posterior regions, accompanied by a hyperexcitable visual cortex. Significance: We provide novel evidence that altered network dynamics in PSE patients are likely a prerequisite for the propagation of the PPR and type-specific responses.

The authors have declared no competing interest.

This study was supported by DRS Research Labs. L.T. L.I. and T.D. received support from the Swiss Epilepsy Foundation.

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The Ethics Committee of Kantonale Ethikkommission Zurich gave ethical approval for this work

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