Brain development: anatomy, connectivity, adaptive plasticity, and toxicity.

The developing brain is inherently more vulnerable to injury than the adult brain because brain development is extraordinarily complex, with periods of unique susceptibility. When brain developmental processes are suspended or delayed by any external influence, virtually no potential exists for subsequent regeneration and repair. This inevitably leads to long-lasting or permanent consequences. Recent genetic studies have contributed to a better understanding of the dynamic adaptive changes that occur in the developing brain as a consequence of genetic and environmental processes. Many industrial and environmental chemicals such as lead, methyl-mercury, polychlorinated biphenyls, arsenic, and toluene are recognized causes of neurodevelopmental disorders that lead to clinical or subclinical brain dysfunction. A number of these developmental disabilities arise from interactions between environmental factors and individual gene susceptibility. In addition, neurodevelopmental disorders of unknown origin, such as mental retardation, attention deficit disorder, cerebral palsy, and autism are becoming increasingly prevalent, with costly consequences for the family and society. The aim of this review is examine brain developmental anatomy, connectivity, adaptive plasticity, and toxicity in the context of current knowledge and future trends.