Sculpting the developing brain.

The developing brain experiences major construction during fetal life and for at least the first decade of childhood. Many more neurons and synoptic connections are produced than are needed for later function, and the mature brain is what remains after these excess building materials are "sculpted" away. This process is thought to be the basis for the developing brain's plasticity, or the capacity to adapt its behavior and circuitry to stimulation from the external environment. Plastic reorganization of the brain is now being studied in children and adults with new noninvasive tools such as functional brain magnetic resonance imaging. This exploratory tool and other new clinical methods demonstrate how the brain's functional "maps" undergo major reorganization in response to early environmental changes. The neurobiology of brain reorganization during development is also being studied with use of new insights into the molecular mechanisms for activity-dependent neuronal plasticity. Clinical disorders such as lead poisoning, metabolic and epileptic encephalopathies, and psychosocial deprivation may arise from disrupted brain plasticity. Several mental retardation syndromes and cognitive disorders recently recognized as being secondary to genetic disruption of intracellular signaling cascades may also disrupt this process. Understanding how the brain's circuitry is sculpted during development provides an important perspective for thinking about neurodevelopmental disorders.