Abstract
The adult human brain is arguably the most complex of biological systems. It contains 86 billion neurons (the information processing cells of the brain) and many more support cells. The neurons, with the assistance of the support cells, form trillions of connections creating complex, interconnected neural networks that support all human thought, feeling, and action. A challenge for modern neuroscience is to provide a model that accounts for this exquisitely complex and dynamic system. One fundamental part of this model is an account of how the human brain develops. This essay describes two important aspects of this developmental story. The first part of the story focuses on the remarkable and dynamic set of events that unfold during the prenatal period to give rise to cell lineage that form the essential substance of the brain, particularly the structures of the cerebral hemispheres. The second part of the story focuses on the formation of the major brain pathways of the cerebrum, the intricate fiber bundles that connect different populations of neurons to form the information processing systems that support all human thought and action. These two aspects of early brain development provide an essential foundation for understanding how the structure, organization, and functioning of the human brain emerge. WIREs Cogn Sci 2017, 8:e1409. doi: 10.1002/wcs.1409 For further resources related to this article, please visit the WIREs website.
Highlights
Evolution has selected for a developmental process by which the exquisite structure of the human brain appears to unfold miraculously
A pool of neural progenitor cells that appears only 3 weeks after conception will produce all of the other cell types in the brain, but these different cell lines emerge in response to different molecular signals, from different regions in the proliferative zone, and at different times
During development a general principle is that cells, and later connections between cells, are produced in much greater numbers than the numbers of surviving cell populations and connections, and the pruning back is essential for normal function of the neural circuits they form
Summary
Evolution has selected for a developmental process by which the exquisite structure of the human brain appears to unfold miraculously. As we uncover the molecular and cellular interactions that drive these developmental processes, we recognize that the system is evolving over time via countless signals exchanged between cells and groups of cells in many local communities throughout the growing brain. These developmental events resemble the kinds of interactions that occur among people as they come and go from a rapidly growing and constantly changing frontier town. This essay considers the series of remarkable structural changes that, over time, give rise to the complex architecture of the mature human brain. First, the development of the cell lines that make up neural structures, and the processes by which the circuits, pathways, and information processing networks of the human brain emerge
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