Assessing the EEG reactivity to photic stimulation in the sedated epileptic brain

The default mode network`s (DMN) can be investigated using default EEG reactivity (DER).The default oscillatory macrostate (DEM) is exemplified by the macrostate showing thehighest decrease in occurrence probability during intermittent photic stimulation (IPS).This study aimed to investigate DER, in the deeply sedated epileptic brain.We used a genetic rat model of absence epilepsy, the adult Wistar Albino Glaxo Rijwijk(WAG/Rij) rat. Controls consisted of age-matched Wistar rats.Deep aesthetic coma was induced by chloral hydrate. We performed cortical EEG recordingsduring the induced altered state of conciousness and the subsequent recovery. One eyereceived IPS in 1-minute epochs with 0.5 Hz. Visual evoked potential (VEP) was assessed byEEG of the fronto-occipital region contralateral to the stimulus while ipsilateral EEG wasused to investigate DER by calculating the decrease in DEM occurrence ratio (DEMR)during IPS compared to a 1-minute epoch before stimulation. The fraction of time spent insuppression over 1-minute intervals defined the suppression ratio (SR) during BS.The SR before stimulation was 50% - 80%. DEM was represented by the suppression periodof the BS so that DEMR was statistically indiscernible from SR. A decrease in DEMoccurrence was caused by IPS without triggering spike-and-wave discharges. The DER waslarger in WAG/Rij as compared to controls for the same DEMR before stimulation. Thedifference was decreased following ethosuximide.Our data suggests that interictal functional abnormalities of the WAG/Rij brain could bedetected by DER measurements with implications for the development of new antiseizuremedications.