title: [Development of the isocortex of the human brain during the embryonic and fetal periods up to the 24th week of gestation].
abstract: From 98 specimens (Pr YAKOVLEV's Collection) we have been able to define the cytoarchitectonic criteria of the different stages of the development of the human Isocortex, and to stress some important features of the organogenesis of the human brain. Most of those findings are in agreement with G.I. POLIAKOV's publications on the cerebral development. Schematically it is possible to individualise three periods made of several stages: - The first one, from the 4th to the 6th week of Gestation during which the primitive neural epithelium, with its four layers (layers of His), is built up. - The second period, from the 7th to the 14th week, includes the two main tides of neuronal migration, separated by a period of recession. So, 4 cytoarchitectonic types of cortical plate may be described: type A. B. C. and D. - Thr third period is that of the stratification of the homogeneous Cortical Plate of type D, leading it through the patterns E I, II, III, IV to the stage of a six-layered Isocortex (24w). Beside this analytical description of the stages of development, the cytoarchitectonic criteria are able to give an ontogenetic evidence of the fundamental difference, already established by P. I. YAKOVLEV on neuropathological and neuroanatomical grounds, between the frontal, epipyriform Isocortex, and the caudal, epihippocampal Isocortex. During each of the stages described above, it is possible indeed to analyse specific features of one or the other part of the hemispheric wall and to determine a borderline between these two parts. Furthermore the temporal sequence of the events occurring inside the Isocortical Plate is slightly different in both parts, increasing the cytoarchitectonic contrast between them. In summary, such a study gives not only a precise definition of the ontogenetic stages of development of the Isocortex but also a better understanding of the organogenesis of the human brain, and by this way, it may be helpful in the analysis of the malformations of the Nervous System.
mesh_terms: D002452:Cell Count; D002454:Cell Differentiation; D002465:Cell Movement; D002540:Cerebral Cortex / Q000166:cytology / Q000196:embryology*; D005865:Gestational Age; D006801:Humans; D009474:Neurons / Q000166:cytology / Q000502:physiology
vernacular_title: Développement de l'isocortex du cerveau humain pendant les périodes embryonnaires et foetales jusqu'à la 24 éme semaine de gestation