Summary
Contents
Subject index
This affordable paperback course textbook has been adapted from the landmark four-volume Handbook of Applied Developmental Science (SAGE 2003). In 20 chapters, Applied Developmental Science: An Advanced Textbook brings together the latest in theory and application from applied developmental science and the positive psychology movement. This advanced text summarizes and synthesizes the best scientific knowledge from ADS to help readers understand the efforts being made around the world to ensure that all children and adolescents develop into healthy adults who contribute positively to society.
Neural Development and Lifelong Plasticity
Neural Development and Lifelong Plasticity
The formation and growth of the human brain is surely one of the most remarkable, albeit unfinished, scientific stories of the past 25 years. Although in the United States, the 1990s were declared to be the “decade of the brain,” it is clear as we enter the early 21st century that our knowledge of brain function and development is far from complete. A point I hope to emphasize throughout this chapter is that knowledge of brain development is surely critical to understanding all of child development. 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 the following pages that brains desperately need both endogenous and exogenous experiences to grow properly. This is particularly true during the postnatal period, in which, unfortunately, the least is known about brain development.
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 proceed to talk about the role of experience in influencing the brain. I will do so by drawing on the role of early as well as late experience to make the point 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
As students of human embryology are aware, 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 two layers. The outer layer will become support structures, such as the amniotic sac, umbilical cord, and placenta, whereas the inner layer will become the embryo itself. Over the course of the next week, the embryo begins to subdivide into layers, and it is from the outer, ectodermal layer that the nervous system will form. How this miraculous transformation occurs, from a thin layer of unspecified tissue into the highly complex organ known as the brain, is the subject of intense study. In the following section, the major prenatal and postnatal events that give rise to the human brain are described. The major prenatal events consist of neural induction and neurulation, cell proliferation and migration, followed by differentiation, apoptosis (cell death), and axonal outgrowth. Myelination and synaptogenesis begin prenatally (subsequent to the formation of processes, axons, and dendrites), with both processes continuing well into the second decade of life.
AUTHOR'S NOTE: Reproduced with permission from Millennial Dialogue for Healthy Child Development (MDC), Toronto, Canada.
Prenatal Development
Neural Induction
As illustrated in Figure 2.1, neural induction is the process whereby the undiffer-entiated cells that comprise a portion of the ectodermal layer of the embryo go on to become neural tissue itself. In the human, this event occurs at 16 days gestation (O'Rahilly & Gardner, 1979). The mechanisms that permit this ectodermal transformation are still not clear. The traditional view is that a chemical agent is secreted from the mesoderm, which induces the dorsal side (“toward the rear”) of the ectoderm to develop into the nervous system (Spemann & Mangold, 1924). More recent discoveries in developmental neurobiology have revealed that members of the transforming growth factor β (TGF-β) superfamily (e.g., activin) play an important role in induction, whereas several proteins (e.g., follistatin) permit neuralization by inhibiting these TGF-βs (Hemmati-Brivanlou, Kelly, & Melton, 1994).
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