Inter-site EEG relationships before widespread epileptiform discharges

EEG interactions of the background among locations can start to change just before epileptiform discharges. Such interactions were investigated with relative power contribution analysis based on a multivariate autoregressive model, which permits determination of multiple causal relations of EEGs among locations. EEGs from F3, F4, P3, P4, T3 and T4 were examined in 10 epileptic patients with asymmetric spike and wave complexes (SWCs). A 12.5-s epoch just before SWCs was divided into stationary segments throughout 6 locations with a segmentation method. In segments long before SWCs, most power at each location was generated from its own location. In segments immediately preceding SWCs, contributions from other locations, particularly from the hemisphere with smaller SWCs, increased. Overall EEG relationships among 6 locations were examined by an entropy which measures the uniformness of the spatial distribution of power contribution. The entropy significantly increased gradually toward SWCs. Our findings demonstrated stronger interactions among locations just before epileptiform discharges, suggesting a transitional state from background EEG to epileptiform discharges.