21690312 - Development of the Human Cortex and the Concept...

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Development of the Human Cortex and the Concept of “Critical” or “Sensitive” Periods H. B. M. Uylings Royal Netherlands Academy of Sciences VU University Medical Center This review describes the prenatal and postnatal devel- opment of the human cortex. Neurogenesis, neuronal mi- gration, dendrite maturation, synaptogenesis, and white matter development are discussed. In addition, the con- cept of “critical” or “sensitive” periods is discussed as well as genetic and environmental influences (Nature- Nurture). The effects of irradiation, alcohol, smoking, and prenatal maternal influenza and stress on brain func- tions and language performance are reviewed. The pe- riods of plasticity are reviewed for stereoscopic vision, brain lesions, social neglect, and first and second language acquisition. This article illustrates that “critical” or “sensitive” pe- riods exist for those functions for which axonal rewiring across a long distance in the brain is necessary. This is virtually impossible after completion of the develop- mental competition between different axonal systems. I acknowledge the long-standing collaboration with the group of Dr. Ivica Kostovi´c (Croatian Institute for Brain Research, Zagreb, Croatia), and the stimulating discussion with Dr. Kai Kaila (University of Helsinki, Finland) about the issue of genetic and environmental influences on human brain at the IBRO-FENS Summerschool “Development and Plasticity of the Human Cerebral Cortex” at Zadar (September 2005). This discussion led to the com- position of Figure 8 for this review. I thank Ms. W. T. P. Verweij for her secretarial assistance and Mr. H. Stoffels and Mr. G. van der Meulen for their drawings and figures. Correspondence concerning this article should be addressed to H. B. M. Uylings, Netherlands Institute for Neurosciences, Meibergdreef 33, 1105 AZ Amsterdam, The Netherlands. Internet: [email protected] 59
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60 Cortex and “Critical” Periods Furthermore, genotyping allows the maximum of struc- tural and functional properties, but the eventual outcome is under the influence of the environment in positive or negative directions. Under dramatic circumstances, envi- ronmental factors during the first years of life can be quite decisive for the development of language, social, and other intellectual functions. Progress in brain development allows development of cogni- tive capabilities and, in its turn, the exercising of cognitive abili- ties shapes further brain development. Some capabilities (such as binocular vision) can only be developed within rather lim- ited sensitive or “critical” developmental periods. For other ca- pabilities, such as “experience” learning in a so-called enriched environment, such restricted developmental time windows do not exist (e.g., Uylings, 2001) because of the plasticity potential of the underlying brain circuitry elements necessary for these abilities. Various cognitive functions are involved in mastering a sec-
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21690312 - Development of the Human Cortex and the Concept...

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