ABSTRACT

The basis of development in a human being lies in the head, in the brain. Foetuses without brains do not survive. Genetic influence sets the general structural framework of the brain and turns genes on and off at certain points in development that are determined in many cases by environmental influences. In the very early growth of the brain growth cone cells lead the migration of neurons to the head end of the embryo. The progress of these cones and their following neurons is genetically controlled and thus determine the general structure of the brain. The rate at which the brain matures dictates the general pace of development in children. The overall process of selection of certain neural structures, and the competitive elimination of others, which occurs in infancy, has been called 'parcellation'. This process is essential because development in this period often requires the creation of structures and functions necessary only for a time limited period of growth.