The brain is a kind of very large-scale integration circuit or its beyond that produces extremely various ranges of electroencephalogram. Epilepsy is a state caused by explosively hyperexcitable brain activities. Recently, it has been suggested that not only the hyperexcitability of neurons but also glial cells, which were previously thought to be silent or plain, play a crucial role in the acquisition of epileptogenicity. In this review article, we will comprehensively describe the utility of the analysis of brain activities from extremely low to high frequency oscillations. Our multi-institute study confirmed that ictal direct current shifts (ictal DC) precedes ictal high-frequency oscillations (ictal HFOs), being more prominent in neocortical epilepsy than in temporal lobe epilepsy. Moreover, we revealed that the complete resection of the core regions of ictal DC shifts significantly correlated with favorable outcomes after epileptic surgery. Taking our findings and previous knowledge into account, we will address the importance of not only neuronal but also glial functions towards the better understanding of pathogenesis of the so-called "chronic" state of epilepsy.