The brain of a child develops vision and other capacities during what is called a “critical period,” a time when the brain is primed to undergo lasting change once exposed to sensory and social stimuli. These intervals allow for the molding and shaping of neural connections. A growing understanding of the dynamics of the critical period is allowing scientists to contemplate drugs and behavioral measures to reinstate critical periods later in life to correct early developmental problems. Watch Harvard neuroscientist Takao Hensch—author of an article on critical periods in the February issue of Scientific American—as he discusses the shaping of neural circuits by early experience.