INTRODUCTION
In recent years, parents and policymakers have become increasingly interested in the potential role of positive early childhood experiences in promoting a child’s emotional and intellectual well-being. Much of this interest has been sparked by numerous articles in the popular press claiming that recent advances in brain research can give parents guidance about everything from buying toys to choosing a preschool. While this growing interest in early childhood and the impact of early life experience is unquestionably a good thing, it has also contributed to the spread of sometimes inaccurate and frequently misunderstood information about what conclusions can be drawn from our knowledge of brain development. This brief reviews the research about early childhood brain development in order to provide policymakers with some of the information they need to consider as they help parents create a healthy and stimulating environment in which their children can grow. The excitement about brain development in infancy and early childhood is well justified by the research, but caution must be exercised in drawing conclusions for parents and public policy at a time when the research and knowledge base is evolving rapidly (Cicchetti and Cannon, 1999).
The scientific community has called the years from 1990 to 2000 “the decade of the brain,” because it is during this period, building on the work of the preceding two decades, that our understanding of brain development increased exponentially. In this brief, we have attempted to identify key scientific principles that emerge from intensive efforts to unravel the cellular and physiologic basis for brain development in humans. As is the case in any field of scientific study, even these basic principles are open to challenges by new information. For example, in the past two years, articles in Science magazine and proceedings of the National Academy of Science, as reported on the front page of the New York Times, presented new findings suggesting that one piece of scientific orthodoxy – that individuals are born with all the brain cells they ever have - may be incorrect. The articles describe a series of experiments demonstrating that, in fact, parts of the monkey cortex responsible for memory formation and consolidation (the hippocampus) may grow new brain cells on a daily basis. Thus, while we have provided a summary of our knowledge of brain development, readers should keep in mind that scientific investigation continually expands our understanding in new and sometimes unexpected directions.
WHAT DO WE KNOW ABOUT BRAIN DEVELOPMENT?
Like much of human development, the development of the human brain is the result of a complex interaction between nature and nurture, between the unique genetic code an individual inherits and his or her experience both before and after birth. Recent research in the fields of neurobiology and developmental psychology provides evidence of the specific processes involved in human brain development, particularly the process by which even the earliest experience affects brain development. Much of what we know about human brain development is derived from studies that involve extensive and invasive experimentation on rats, monkeys and other animals. These experiments enable researchers to directly observe brain development by measuring and comparing physiologic processes directly from the brains of animals reared under various conditions. Researchers use these direct measures of brain functioning to draw conclusions about the effect of various types of experiences on brain development.