Neural progenitor cells and developing neurons show periodic, synchronous Ca2+ rises even before synapse formation, and the origin of the synchronous activity remains unknown. Here, fluorescence measurement revealed that the membrane potential of the nuclear envelope, which forms an intracellular Ca2+ store, changed with a release of Ca2+ and generated spontaneous, periodic bursts of fluctuations in potential. Furthermore, changes in the nuclear envelope's potential underlay spike burst generations. These results support the model that voltage fluctuations of the nuclear envelope synchronize Ca2+ release between cells and also function as a current noise generator to cause synchronous burst discharges. (C) 2011 Elsevier Inc. All rights reserved.