Over the past several decades, significant advances have been made in our understanding of the basic stages and mechanisms of mammalian brain development. Studies elucidating the neurobiology of brain development span the levels of neural organization from the macroanatomic, to the cellular, to the molecular. Together this large body of work provides a picture of brain development as the product of a complex series of dynamic and adaptive processes operating within a highly constrained, genetically organized but constantly changing context. The view of brain development that has emerged from the developmental neurobiology literature presents both challenges and opportunities to psychologists seeking to understand the fundamental processes that underlie social and cognitive development, and the neural systems that mediate them. This chapter is intended to provide an overview of some very basic principles of brain development, drawn from contemporary developmental neurobiology, that may be of use to investigators from a wide range of disciplines.
Over the past three decades there has been tremendous progress in our understanding of the basic principles of neural development. This progress has changed our fundamental models of how brains develop. Strongly deterministic models have given way to more dynamic and interactive models anchored in the process of development, itself. As suggested by the examples presented in this paper, the processes that underlie and guide brain development involve the ongoing interplay of genetic and environmental factors. Brains do not develop normally in the absence of critical genetic signaling and they do not develop normally in the absence of essential environmental input. Rather, at each point in development, organism intrinsic and environmental factors interact to support the increasingly complex and elaborate structures and functions of the brain. During the embryologic period the interactive processes are most prominent at the level of cell-cell interactions where gene expression in one population of cells generates molecular signals that alter the developmental course of another population of cells. However, even during this earliest period, interactions involving factors in the external environment also play essential roles in the development of the embryonic brain. During the fetal and postnatal periods, organism intrinsic factors continue to play a critical role in development, but across this extended period a wide array of factors in the external world influence the course of brain development in increasingly prominent ways.
Although nothing in neural development appears to be “predetermined”, the process of development is nonetheless orderly and follows very regular patterns over time. The regularity of developmental process arises from constraints imposed by both genetic and environmental factors. Genes provide the templates for creating particular proteins that are essential to the developmental process; the environment provides essential input that shapes and influences the direction of the emerging neural networks. A third essential constraint arises from the fact that the developmental process unfolds over time. The integrity of the developmental process depends absolutely upon the availability of the right neural elements appearing at the appropriate moment in developmental time. Often the emergence of a new element depends upon developmental events that immediately precede its appearance. For example, the differentiation of the neural progenitor cells along the axial midline of the neural plate during gastrulation sets the stage for the formation of the ventricular zone during neurulation. Furthermore, at each point in developmental time the organism has both a state and a history that limit which factors can influence its development. Visual and auditory signals have little effect on the gastrulating embryo, but both are essential for the typical development of vision and audition in the newborn. The constructs of “progressive differentiation” and “progressive commitment” capture important aspects of the temporal nature of brain development and can account for the regularities that are observed (Stiles 2008). At all levels of the neural system, progressive differentiation of specific elements and structures coupled with progressive commitment of those elements to functional systems appear to be the governing principles of brain development.
Stiles, J., & Jernigan, T. L. (2010). The basics of brain development. Neuropsychology Review, 20(4), 327–348. https://doi.org/10.1007/s11065-010-9148-4
― 3 Nov 2010
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