▪ Abstract Neuronal circuits are shaped by experience during critical periods of early
postnatal life. The ability to control the timing, duration, and closure of these heightened
levels of brain plasticity has recently become experimentally accessible, especially in the
developing visual system. This review summarizes our current understanding of known
critical periods across several systems and species. It delineates a number of emerging
principles: functional competition between inputs, role for electrical activity, structural …