P366 Multimodal EEG/ECOG and fast optical signal measurements in interictal epileptic spikes

Abstract

Objectives Although many studies in epilepsy have examined the synaptic mechanisms constituting the basis for most of the current principles of brain activity, relatively less studies have tried to characterize changes in the cellular environment that might predispose a network to pathologic synchronization. Methods In this study, near-infrared optical imaging was used with ECoG and EEG to investigate variations in the optical properties of cortical tissue directly associated with neuronal activity in 15 rats and 3 human epileptic patients. Time-frequency analysis was also used to track variations of (de) synchronization concomitantly with changes in optical signals during IES. Results Changes in Fast optical signals (FOS) occurred 320 ms before to 370 ms after the IES peak. These changes started before any changes in ECoG signal. In addition, time-frequency domain ECoG revealed an alternating decrease-increase-decrease in the ECoG spectral power (pointing to desynchronization-synchronization-desynchronization), which occurred concomitantly with an increase-decrease-increase in relative optical signal (pointing to shrinking-swelling-shrinking of the neuronal assembly) during the IES. Discussion These relationships between electrical and optical changes highlights the complexity of the interplay between the neuronal network activity and its environment around an IES. Conclusions These changes in the neuronal environment around IESs raise new questions about the mechanisms that provides the suitable conditions for the neuronal synchronization during IESs. Significance The multimodal-multiscale FOS-ECoG approach opens new avenues to better analyze the mechanisms of neuronal synchronization in the pathologic epileptic brain, which is applicable in clinic.