Functional network dynamics in photosensitive epilepsy depend on stimulation frequency and photoparoxysmal electroencephalographic response.

OBJECTIVE

Photosensitive epilepsy (PSE) is a reflex epilepsy, where abnormal electroencephalographic (EEG) responses are induced by photic stimulation. Photosensitivity is classified into four types based on the propagation of the brain's response to visual stimuli. Here, we aimed to describe the underlying dynamical mechanisms of PSE and different photosensitivity types.

METHODS

This retrospective study included healthy controls (HC), PSE patients, and non-PSE patients with epilepsy (PWE). All participants were stimulated with flickering white light (1-60 Hz) under 10-20 EEG monitoring.

RESULTS

We observed significantly higher occipital photoparoxysmal response (PPR) power in PSE patients compared to HC for stimulation frequencies between 10 and 20 Hz. 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 PSE type 4 compared to HC. Instead, PSE patients exhibited notable differences in functional connectivity for stimulation frequencies of 10-20 Hz in the PPR band (3-4 Hz) relative to HC, characterized by centroparietal and centrofrontopolar hypoconnectivity. Additionally, for the same stimulation frequencies, PSE patients with PPR propagation showed occipitofrontocentral hyperconnectivity compared to both HC and PWE.

SIGNIFICANCE: Our results provide novel evidence that altered network dynamics in PSE patients are likely a prerequisite for the propagation of the PPR and type-specific responses. PSE is a network effect modulated by anterior and anteroposterior hyperconnectivity, supported by a hyperexcitable visual cortex.