Dendritic spines are the major memory elements in the brain, and their properties deeply influence brain functions and disorders. I will introduce recent findings in our laboratory: GABA actions on spine shrinkage and elimination, a critical time window for dopamine on spine enlargement for reinforcement learning, intrinsic turnovers of spines in wild type and fragile X mice, spine enlargement in neocortical pyramidal neurons of awake adult mice, and protein-synthesis dependent optogenetic probes to image and manipulate memory spines and animal behaviors.