Serve and Return Interaction
One of the most essential experiences in shaping the architecture of the developing brain is "serve and return" interaction between children and significant adults in their lives. Young children naturally reach out for interaction through babbling, facial expressions, and gestures, and adults respond with the same kind of vocalizing and gesturing back at them. This back-and-forth process is fundamental to the wiring of the brain, especially in the earliest years.
Still Face Experiment: Dr. Edward Tronick
Using the "Still Face" Experiment, in which a mother denies her baby attention for a short period of time, Tronick describes how prolonged lack of attention can move an infant from good socialization, to periods of bad but repairable socialization. In "ugly" situations the child does not receive any chance to return to the good, and may become stuck.