The formation and growth of the human brain are undoubtedly two of the most remarkable feats of human construction. Although the 1990s were declared the “decade of the brain” in the United States, it is clear as we enter the early twenty-first century that our knowledge of brain function and development is far from complete. Knowledge of brain development is critical to understanding child development, a point made throughout this chapter. In particular, although it is commonly believed that brains develop on their own accord, largely under the direction of genes and hormones, I will make clear in this chapter that brains desperately need both endogenous and exogenous experiences to grow properly. In the sections that follow, I will describe the major events that give rise to the human brain. Once this blueprint is established, I will then discuss the role of experience in influencing the brain. I will do so by drawing on the role of both early and late experience to demonstrate that although brain development is largely limited to the first two decades of life, brain reorganization continues to occur through much of the life span.

BRAIN DEVELOPMENT – A PRÉCIS

Shortly after conception, rapid cell division in the zygote results in the formation of the blastocyst. By the end of the first week, the blastocyst itself has separated into an inner and outer layer.