N-methyl-D-aspartate (NMDA) receptors play an important role in neural plasticity in the central nervous systems (CNSs). We can change our behaviors according to storing things in memory and learning, and the ability is necessary for survival in the daily life. The “learning and memory” is based on experience-dependent neural plasticity in the CNSs. NMDA receptor activation is essential for inducing plastic changes in the structural and functional refinement of synapses and circuits. “Hebbian learning” is an important form of learning and memory. Mg2+ block is a fine equipment of NMDA receptor, and is required to establish“ Hebbian learning”. NMDA receptor activation, however, does not always induce preferred conditions. There are cases that, in particular situations, NMDA receptor activation-dependent plasticity causes pathological conditions. In this review, I will overview the roles of the NMDA receptors in physiological and pathophysiological conditions
