Greenspan has observed three patterns of behavior in infants with overreactive nervous systems. "There is the infant who is easily distracted, irritable, and moody, and the infant who is inhibited, anxious, and tense. A third type of behavior emerges when the infant who is anxious and very cautious attends preschool, for example, and encounters a lot of noise and commotion. It’s as if a switch is flipped in the child’s nervous system, and the child becomes hyperactive, aggressive, and agitated," he said.