Hippocampus is a brain region critically involved in learning and memory. The bidirectional plastic changes of synaptic transmission in this region have been considered as a cellular counterpart of hippocampal learning. In order to elucidate the molecular mechanism of learning and memory, we take a combine molecular and two-photon imaging approaches to visualize the process underlying synaptic plasticity. This revealed rapid translocation of AMPA-type glutamate receptor as well as structural modification of dendritic spines. In this seminar, I will focus on our recent works which address the mechanism of structural plasticity of dendritic spines.