Understanding the role of neural activity in the development of the brain has been a major concern of many modern neurobiologists. The reason is plain enough: since the world influences the brain by means of action potentials and synaptic potentials, activity must be the chief cause of the neural changes wrought by experience. This 1994 volume explores the hypothesis that neural activity generated by experience modulates the ongoing growth of the brain during maturation, thus sculpting in each of us a unique nervous system according to the events of our early life. Brain growth is considered at a macroscopic level by examining brain maps and their modular substructure, and at a cellular level by investigating the neuronal interactions that influence the formation and maintenance of these structures. The ways that experience influences the maturation of the brain at both macroscopic and microscopic levels are described, and the conventional wisdom is re-examined.