Abstract: Sensitive periods refers to that the anatomy and function of brain is ready to be changed due to the specific stimuli. The elaboration of axon, the formation,elimination and consolidation of synapse are the plasticity mechanism during the sensitive periods. The circuit must receive reliable and precise information, and have the adequate connectivity and activate the mechanisms of plasticity in order to open the sensitive periods.

Key words: Sensitive periods, critical periods, plasticity, mechanisms of neuronal circuits