Neurophysiological mechanisms underlying epileptogenesis.

Several factors play a role in the transition from normal to interictal and ictal neuronal activity. While classical data in neocortex suggest that paroxysmal depolarization shift (PDS) accompanied by burst firing (BF) is a giant EPSP, recent data in hippocampal slices show that CA3 neurons are intrinsically capable of generating PDS-BF, mainly due to Ca2+ inward current. Factors of transition from normal to interictal activity are changes in transmembrane ionic currents, GABA disinhibition and BF synchronizing effect. Factors of transition from interictal to ictal activity are changes in extracellular concentration of Ca2+ and K+, cholinergic modulation and BF axonal generation.