During critical period, the heightened plasticity in neocortex opens a time window when, with proper external environmental stimuli, experience dependent refinement processes help to optimize the function of neuronal networks. With the closure of critical periods, the gradually decreased plasticity leaves a mature system which is stable to perform its function but with limited plasticity for changes in the adult. ⋯ Among them, the abundance of AMPA receptor silent synapses, as substrates for Hebbian plasticity, is shown to be closely related to not only critical period plasticity, but also the network refinement at glutamatergic synapses of principal neurons. Here, I discuss the role of silent synapses and how they interact with other known mechanisms involved in critical period plasticity.