The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
Juan F Montiel - One of the best experts on this subject based on the ideXlab platform.
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olfaction navigation and the origin of Isocortex
Frontiers in Neuroscience, 2015Co-Authors: Francisco Aboitiz, Juan F MontielAbstract:There are remarkable similarities between the brains of mammals and birds in terms of microcircuit architecture, despite obvious differences in gross morphology and development. While in reptiles and birds the most expanding component (the dorsal ventricular ridge) displays an overall nuclear shape and derives from the lateral and ventral pallium, in mammals a dorsal pallial, six-layered Isocortex shows the most remarkable elaboration. Regardless of discussions about possible homologies between mammalian and avian brains, a main question remains in explaining the emergence of the mammalian Isocortex, because it represents a unique phenotype across amniotes. In this article, we propose that the origin of the Isocortex was driven by behavioral adaptations involving olfactory driven goal-directed and navigating behaviors. These adaptations were linked with increasing sensory development, which provided selective pressure for the expansion of the dorsal pallium. The latter appeared as an interface in olfactory-hippocampal networks, contributing somatosensory information for navigating behavior. Sensory input from other modalities like vision and audition were subsequently recruited into this expanding region, contributing to multimodal associative networks.
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pallial patterning and the origin of the Isocortex
Frontiers in Neuroscience, 2015Co-Authors: Juan F Montiel, Francisco AboitizAbstract:Together with a complex variety of behavioral, physiological, morphological, and neurobiological innovations, mammals are characterized by the development of an extensive Isocortex (also called neocortex) that is both laminated and radially organized, as opposed to the brain of birds and reptiles. In this article, we will advance a developmental hypothesis in which the mechanisms of evolutionary brain growth remain partly conserved across amniotes (mammals, reptiles and birds), all based on Pax6 signaling or related morphogens. Despite this conservatism, only in mammals there is an additional upregulation of dorsal and anterior signaling centers (the cortical hem and the anterior forebrain, respectively) that promoted a laminar and a columnar structure into the neocortex. It is possible that independently, some birds also developed an upregulated dorsal pallium.
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the evolutionary origin of the mammalian Isocortex towards an integrated developmental and functional approach
Behavioral and Brain Sciences, 2003Co-Authors: Francisco Aboitiz, Daniver Morales, Juan F MontielAbstract:The Isocortex is a distinctive feature of mammalian brains, which has no clear counterpart in the cerebral hemispheres of other amniotes. This paper speculates on the evolutionary processes giving rise to the Isocortex. As a first step, we intend to identify what structure may be ancestral to the Isocortex in the reptilian brain. Then, it is necessary to account for the transformations (developmental, connectional, and functional) of this ancestral structure, which resulted in the origin of the Isocortex. One long-held perspective argues that part of the Isocortex derives from the ventral pallium of reptiles, whereas another view proposes that the Isocortex originated mostly from the dorsal pallium. We consider that, at this point, evidence tends to favor correspondence of the Isocortex with the dorsal cortex of reptiles. In any case, the Isocortex may have originated partly as a consequence of an overall "dorsalizing" effect (that is, an expansion of the territories expressing dorsal-specific genes) during pallial development. Furthermore, expansion of the dorsal pallium may have been driven by selective pressures favoring the development of associative networks between the dorsal cortex, the olfactory cortex, and the hippocampus, which participated in spatial or episodic memory in the early mammals. In this context, sensory projections that in reptiles end in the ventral pallium, are observed to terminate in the Isocortex (dorsal pallium) of mammals, perhaps owing to their participation in these associative networks.
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critical steps in the early evolution of the Isocortex insights from developmental biology
Brazilian Journal of Medical and Biological Research, 2002Co-Authors: Francisco Aboitiz, Juan F Montiel, Javier LopezAbstract:This article proposes a comprehensive view of the origin of the mammalian brain. We discuss i) from which region in the brain of a reptilian-like ancestor did the Isocortex originate, and ii) the origin of the multilayered structure of the Isocortex from a simple-layered structure like that observed in the cortex of present-day reptiles. Regarding question i there have been two alternative hypotheses, one suggesting that most or all the Isocortex originated from the dorsal pallium, and the other suggesting that part of the Isocortex originated from a ventral pallial component. The latter implies that a massive tangential migration of cells from the ventral pallium to the dorsal pallium takes place in isocortical development, something that has not been shown. Question ii refers to the origin of the six-layered Isocortex from a primitive three-layered cortex. It is argued that the superficial isocortical layers can be considered to be an evolutionary acquisition of the mammalian brain, since no equivalent structures can be found in the reptilian brain. Furthermore, a characteristic of the Isocortex is that it develops according to an inside-out neurogenetic gradient, in which late-produced cells migrate past layers of early-produced cells. It is proposed that the inside-out neurogenetic gradient was partly achieved by the activation of a signaling pathway associated with the Cdk5 kinase and its activator p35, while an extracellular protein called reelin (secreted in the marginal zone during development) may have prevented migrating cells from penetrating into the developing marginal zone (future layer I).
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Evolutionary divergence of the reptilian and the mammalian brains: considerations on connectivity and development.
Brain Research Reviews, 2002Co-Authors: Francisco Aboitiz, Daniver Morales, Juan F Montiel, Miguel L. ConchaAbstract:The Isocortex is a distinctive feature of the mammalian brain, with no clear counterpart in other amniotes. There have been long controversies regarding possible homologues of this structure in reptiles and birds. The brains of the latter are characterized by the presence of a structure termed dorsal ventricular ridge (DVR), which receives ascending auditory and visual projections, and has been postulated to be homologous to parts of the mammalian Isocortex (i.e., the auditory and the extrastriate visual cortices). Dissenting views, now supported by molecular evidence, claim that the DVR originates from a region termed ventral pallium, while the Isocortex may arise mostly from the dorsal pallium (in mammals, the ventral pallium relates to the claustroamygdaloid complex). Although it is possible that in mammals the embryonic ventral pallium contributes cells to the developing Isocortex, there is no evidence yet supporting this alternative. The possibility is raised that the expansion of the cerebral cortex in the origin of mammals was product of a generalized dorsalizing influence in pallial development, at the expense of growth in ventral pallial regions. Importantly, the evidence suggests that organization of sensory projections is significantly different between mammals and sauropsids. In reptiles and birds, some sensory pathways project to the ventral pallium and others project to the dorsal pallium, while in mammals sensory projections end mainly in the dorsal pallium. We suggest a scenario for the origin of the mammalian Isocortex which relies on the development of associative circuits between the olfactory, the dorsal and the hippocampal cortices in the earliest mammals.
Karl Zilles - One of the best experts on this subject based on the ideXlab platform.
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Chapter 22 – Isocortex
The Rat Nervous System, 2020Co-Authors: Nicola Palomero-gallagher, Karl ZillesAbstract:The cerebral cortex can be subdivided either into: Isocortex and allocortex based on histological criteria; homogenetic and heterogenetic based on layer development timelines; or neocortex, paleocortex and archicortex based on evolutionary criteria. The Isocortex comprises of the phylogenetically youngest cortical areas, which develop a six-layered structure during fetal stages and maintain this lamination pattern in adulthood. Thus, it resembles the evolutionary defined neocortex and the developmentally defined homogenetic cortex. Differences in laminar architecture and connectivity patterns enable a parcellation of the Isocortex into motor, or unimodal or multimodal associative sensory regions and areas. Aims of this chapter are to describe a parcellation scheme of the rat Isocortex based on cyto-, myelo- and receptor-architectonical data, in the framework of the three currently existing comprehensive parcellation schemes of the rat cortex, and discuss insights into the hierarchical organization of rat isocortical areas provided by their receptor architecture.
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The Human Nervous System (Second Edition) - CHAPTER 27 – Architecture of the Human Cerebral Cortex: Regional and Laminar Organization
The Human Nervous System, 2020Co-Authors: Karl ZillesAbstract:The cerebral cortex of the human brain can be subdivided by microscopic anatomical criteria into two major parts, Isocortex and allocortex. Despite regional variations, the largest part of the adult human Isocortex is characterized by its six-layered structure visible in cell body-stained sections. In contrast to the six-layered architecture of the Isocortex, the laminar pattern of the allocortex shows a regionally highly variable appearance reaching from a hardly subdivisible single-cell band to a highly differentiated architecture with more than 10 layers. The Isocortex contains primary sensory areas, which are main targets of unimodal sensory afferents originating in the ventroposterior nucleus of the thalamus, medial and lateral geniculate bodies, respectively. These primary areas project to a whole set of higher order unimodal sensory areas in a hierarchical and parallel organization. The higher order unimodal sensory cortices border to multimodal association areas. Uni- and multimodal areas send projections to the motor cortex, which is again subdivided into a primary motor area and nonprimary motor areas.
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chapter 22 Isocortex
The Rat Nervous System (Fourth Edition), 2015Co-Authors: Nicola Palomerogallagher, Karl ZillesAbstract:The cerebral cortex can be subdivided either into: Isocortex and allocortex based on histological criteria; homogenetic and heterogenetic based on layer development timelines; or neocortex, paleocortex and archicortex based on evolutionary criteria. The Isocortex comprises of the phylogenetically youngest cortical areas, which develop a six-layered structure during fetal stages and maintain this lamination pattern in adulthood. Thus, it resembles the evolutionary defined neocortex and the developmentally defined homogenetic cortex. Differences in laminar architecture and connectivity patterns enable a parcellation of the Isocortex into motor, or unimodal or multimodal associative sensory regions and areas. Aims of this chapter are to describe a parcellation scheme of the rat Isocortex based on cyto-, myelo- and receptor-architectonical data, in the framework of the three currently existing comprehensive parcellation schemes of the rat cortex, and discuss insights into the hierarchical organization of rat isocortical areas provided by their receptor architecture.
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chapter 27 architecture of the human cerebral cortex regional and laminar organization
The Human Nervous System (Second Edition), 2004Co-Authors: Karl ZillesAbstract:The cerebral cortex of the human brain can be subdivided by microscopic anatomical criteria into two major parts, Isocortex and allocortex. Despite regional variations, the largest part of the adult human Isocortex is characterized by its six-layered structure visible in cell body-stained sections. In contrast to the six-layered architecture of the Isocortex, the laminar pattern of the allocortex shows a regionally highly variable appearance reaching from a hardly subdivisible single-cell band to a highly differentiated architecture with more than 10 layers. The Isocortex contains primary sensory areas, which are main targets of unimodal sensory afferents originating in the ventroposterior nucleus of the thalamus, medial and lateral geniculate bodies, respectively. These primary areas project to a whole set of higher order unimodal sensory areas in a hierarchical and parallel organization. The higher order unimodal sensory cortices border to multimodal association areas. Uni- and multimodal areas send projections to the motor cortex, which is again subdivided into a primary motor area and nonprimary motor areas.
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afferents to different layers of the dorsolateral Isocortex in rats
Anatomy and Embryology, 1995Co-Authors: Ivan Divac, Jesper Mogensen, Jose Regidor, Slobodan Milosevic, Karl ZillesAbstract:Fluorescent somatopetal tracers were used to infiltrate, by diffusion rather than injections, the dorsolateral cortex of one hemisphere in rats. In different animals the tracers penetrated into the cortex to different depths. We found several interesting features of the commissural system: first, there were no areas without commissural neurons. At least a few labelled cell bodies were present in a single-cell layer also in “acallosal” cortical areas. Secondly, there is a considerable variety of laminar distribution patterns of labelled perikarya in different areas. Thirdly, some cortical fields, which cytoarchitecturally appear uniform, can be subdivided according to different distributions of cell bodies with commissural projections. Fourthly, when only supragranular layers were infiltrated, labelled cell bodies were present mainly in the supragranular layers of the contralateral cortex. Infiltration of the first layer alone did not label any neurons in the contralateral cortex but did label neurons in layer VIb ipsilaterally. In the subcortex, the labelled perikarya were found in the structures already known to project directly to the cortex. In rats with the tracer restricted mainly to the supragranular layers, a conspicuously reduced labelling was found in the basal forebrain and the thalamus. In the thalami of those animals, labelled neurons were found only in paralamellar nuclei. The high sensitivity of the tracer used, together with infiltration of the entire dorsolateral cortex, allows us to conclude that probably all sources of innervation of the Isocortex in rats have been seen.
Francisco Aboitiz - One of the best experts on this subject based on the ideXlab platform.
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An interdisciplinary approach to brain evolution: A long due debate
Behavioral and Brain Sciences, 2020Co-Authors: Francisco Aboitiz, Daniver Morales, Juan MontielAbstract:A dorsalization mechanism is a good candidate for the evolutionary origin of the Isocortex, producing a radial and tangential expansion of the dorsal pallium (and perhaps other structures that acquired a cortical phenotype). Evidence suggests that a large part of the dorsal ventricular ridge (DVR) of reptiles and birds derives from the embryonic ventral pallium, whereas the Isocortex possibly derives mostly from the dorsal pallium. In early mammals, the development of olfactory-hippocampal associative networks may have been pivotal in facilitating the selection of a larger and more complex dorsal pallium which received both collothalamic and lemnothalamic sensory information. Finally, although it is not clear exactly when mammalian brain expansion began, fossil evidence indicates that this was a late event in mammaliaform evolution.
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olfaction navigation and the origin of Isocortex
Frontiers in Neuroscience, 2015Co-Authors: Francisco Aboitiz, Juan F MontielAbstract:There are remarkable similarities between the brains of mammals and birds in terms of microcircuit architecture, despite obvious differences in gross morphology and development. While in reptiles and birds the most expanding component (the dorsal ventricular ridge) displays an overall nuclear shape and derives from the lateral and ventral pallium, in mammals a dorsal pallial, six-layered Isocortex shows the most remarkable elaboration. Regardless of discussions about possible homologies between mammalian and avian brains, a main question remains in explaining the emergence of the mammalian Isocortex, because it represents a unique phenotype across amniotes. In this article, we propose that the origin of the Isocortex was driven by behavioral adaptations involving olfactory driven goal-directed and navigating behaviors. These adaptations were linked with increasing sensory development, which provided selective pressure for the expansion of the dorsal pallium. The latter appeared as an interface in olfactory-hippocampal networks, contributing somatosensory information for navigating behavior. Sensory input from other modalities like vision and audition were subsequently recruited into this expanding region, contributing to multimodal associative networks.
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pallial patterning and the origin of the Isocortex
Frontiers in Neuroscience, 2015Co-Authors: Juan F Montiel, Francisco AboitizAbstract:Together with a complex variety of behavioral, physiological, morphological, and neurobiological innovations, mammals are characterized by the development of an extensive Isocortex (also called neocortex) that is both laminated and radially organized, as opposed to the brain of birds and reptiles. In this article, we will advance a developmental hypothesis in which the mechanisms of evolutionary brain growth remain partly conserved across amniotes (mammals, reptiles and birds), all based on Pax6 signaling or related morphogens. Despite this conservatism, only in mammals there is an additional upregulation of dorsal and anterior signaling centers (the cortical hem and the anterior forebrain, respectively) that promoted a laminar and a columnar structure into the neocortex. It is possible that independently, some birds also developed an upregulated dorsal pallium.
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Functional constraints in the evolution of brain circuits
Frontiers in Neuroscience, 2015Co-Authors: Conrado A. Bosman, Francisco AboitizAbstract:Regardless of major anatomical and neurodevelopmental differences, the vertebrate Isocortex shows a remarkably well-conserved organization. In the Isocortex, reciprocal connections between excitatory and inhibitory neurons are distributed across multiple layers, encompassing modular, dynamical and recurrent functional networks during information processing. These dynamical brain networks are often organized in neuronal assemblies interacting through rhythmic phase relationships. Accordingly, these oscillatory interactions are observed across multiple brain scale levels, and they are associated with several sensory, motor, and cognitive processes. Most notably, oscillatory interactions are also found in the complete spectrum of vertebrates. Yet, it is unknown why this functional organization is so well conserved in evolution. In this perspective, we propose some ideas about how functional requirements of the Isocortex can account for the evolutionary stability observed in microcircuits across vertebrates. We argue that Isocortex architectures represent canonical microcircuits resulting from: (i) the early selection of neuronal architectures based on the oscillatory excitatory-inhibitory balance, which lead to the implementation of compartmentalized oscillations and (ii) the subsequent emergence of inferential coding strategies (predictive coding), which are able to expand computational capacities. We also argue that these functional constraints may be the result of several advantages that oscillatory activity contributes to brain network processes, such as information transmission and code reliability. In this manner, similarities in mesoscale brain circuitry and input-output organization between different vertebrate groups may reflect evolutionary constraints imposed by these functional requirements, which may or may not be traceable to a common ancestor.
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the evolutionary origin of the mammalian Isocortex towards an integrated developmental and functional approach
Behavioral and Brain Sciences, 2003Co-Authors: Francisco Aboitiz, Daniver Morales, Juan F MontielAbstract:The Isocortex is a distinctive feature of mammalian brains, which has no clear counterpart in the cerebral hemispheres of other amniotes. This paper speculates on the evolutionary processes giving rise to the Isocortex. As a first step, we intend to identify what structure may be ancestral to the Isocortex in the reptilian brain. Then, it is necessary to account for the transformations (developmental, connectional, and functional) of this ancestral structure, which resulted in the origin of the Isocortex. One long-held perspective argues that part of the Isocortex derives from the ventral pallium of reptiles, whereas another view proposes that the Isocortex originated mostly from the dorsal pallium. We consider that, at this point, evidence tends to favor correspondence of the Isocortex with the dorsal cortex of reptiles. In any case, the Isocortex may have originated partly as a consequence of an overall "dorsalizing" effect (that is, an expansion of the territories expressing dorsal-specific genes) during pallial development. Furthermore, expansion of the dorsal pallium may have been driven by selective pressures favoring the development of associative networks between the dorsal cortex, the olfactory cortex, and the hippocampus, which participated in spatial or episodic memory in the early mammals. In this context, sensory projections that in reptiles end in the ventral pallium, are observed to terminate in the Isocortex (dorsal pallium) of mammals, perhaps owing to their participation in these associative networks.
Barbara L. Finlay - One of the best experts on this subject based on the ideXlab platform.
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evolution of cytoarchitectural landscapes in the mammalian Isocortex sirenians trichechus manatus in comparison with other mammals
The Journal of Comparative Neurology, 2016Co-Authors: Christine J Charvet, Roger L. Reep, Barbara L. FinlayAbstract:The Isocortex of several primates and rodents shows a systematic increase in the number of neurons per unit of cortical surface area from its rostrolateral to caudomedial border. The steepness of the gradient in neuronal number and density is positively correlated with cortical volume. The relative duration of neurogenesis along the same rostrocaudal gradient predicts a substantial fraction of this variation in neuron number and laminar position, which is produced principally from layers II–IV neurons. However, virtually all of our quantitative knowledge about total and laminar variation in cortical neuron numbers and neurogenesis comes from rodents and primates, leaving whole taxonomic groups and many intermediate-sized brains unexplored. Thus, the ubiquity in mammals of the covariation of longer cortical neurogenesis and increased cortical neuron number deriving from cortical layers II–IV is undetermined. To begin to address this gap, we examined the Isocortex of the manatee using the optical disector method in sectioned tissue, and also assembled partial data from published reports of the domestic cat brain. The manatee Isocortex has relatively fewer neurons per total volume, and fewer II–IV neurons than primates with equivalently sized brains. The gradient in number of neurons from the rostral to the caudal pole is intermediate between primates and rodents, and, like those species, is observed only in the upper cortical layers. The cat Isocortex (Felis domesticus) shows a similar structure. Key species for further tests of the origin, ubiquity, and significance of this organizational feature are discussed. J. Comp. Neurol., 2015. © 2015 Wiley Periodicals, Inc.
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evo devo and the primate Isocortex the central organizing role of intrinsic gradients of neurogenesis
Brain Behavior and Evolution, 2014Co-Authors: Christine J Charvet, Barbara L. FinlayAbstract:Spatial gradients in the initiation and termination of basic processes, such as cytogenesis, cell-type specification and dendritic maturation, are ubiquitous in developing nervous systems. Such gradie
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systematic balancing gradients in neuron density and number across the primate Isocortex
Frontiers in Neuroanatomy, 2012Co-Authors: Diarmuid J Cahalane, Christine J Charvet, Barbara L. FinlayAbstract:The cellular and areal organization of the cerebral cortex impacts how it processes and integrates information. How that organization emerges and how best to characterize it has been debated for over a century. Here we demonstrate and describe in the isocortices of seven primate species a pronounced, anterior-to-posterior gradient in the density of neurons and in the number of neurons under a unit area of the cortical surface. Our findings assert that the cellular architecture of the primate Isocortex is neither arranged uniformly nor into discrete patches with an arbitrary spatial arrangement. Rather, it exhibits striking systematic variation. We conjecture that these gradients, which establish the basic landscape that richer areal and cellular structure is built upon, result from developmental patterns of cortical neurogenesis which are conserved across species. Moreover, we propose a functional consequence: that the gradient in neurons per unit of cortical area fosters the integration and dimensional reduction of information along its ascent through sensory areas and towards frontal cortex.
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The cortex in multidimensional space: where do cortical areas come from?
Developmental Science, 2001Co-Authors: Marcy A Kingsbury, Barbara L. FinlayAbstract:The concept of a cortical ‘area’ as a discrete phylogenetic, developmental and computational unit is evaluated. Evidence including the comparative organization of the forebrain in vertebrates, the organization of cortex in different mammals, the scaling of the areas of the Isocortex in mammals, and the early molecular differentiation of the cortex all suggest a special status for the primary sensory cortical areas, particularly the visual cortex. Furthermore, the overlapping gradients of early molecular expression and the patterning of cortical structure and connectivity by thalamic input suggest a new view of cortical organization that is different from the traditional view of a developmentally mosaic cortex; this view proposes that distinct cortical areas arise combinatorily from the multiple overlapping processes imposed upon the developing cortex.
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what about Isocortex can be rewired and reconfigured
1997Co-Authors: J K Niederer, Marcy A Kingsbury, Barbara L. FinlayAbstract:The mammalian Isocortex is an intriguing mix of structural consistency and functional diversity. Across mammals, Isocortex configuration is conserved to a very high degree, with visual cortex posterior, somatosensory cortex medial, and the associated secondary areas proximal to these primary areas. The classic, six- layered internal cortical architecture is conserved. Yet, cortical areas are also structurally and functionally distinct and can be distinguished on the basis of architecture, biochemistry, physiology and connectivity. Across species, the differences between areas are remarkably consistent. Is there something special about each cortical area that makes it adept at handling its particular input, or is it just a piece of a calculating machine that is indifferent to the modality of its information and simply performs routine transformations? If there are true differences in the cortical mosaic, when in development do they arise, and what feature of gene expression, connectivity or function carries the information that diversifies cortical areas?
Henry Kennedy - One of the best experts on this subject based on the ideXlab platform.
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the timetable of laminar neurogenesis contributes to the specification of cortical areas in mouse Isocortex
The Journal of Comparative Neurology, 1997Co-Authors: Franck Polleux, Colette Dehay, Henry KennedyAbstract:In the primate visual cortex, the birthdate of neurons in homologous layers differ on either side of the 17-18 border suggesting that there might be different timetables of laminar histogenesis in these two areas (Dehay et al. [1993] Nature 366:464‐466 and Kennedy et al. [1996] Soc. Neurosci. Abst. 22:525). Because of the potential importance of these findings for understanding mechanisms that generate areal identity, we have developed an experimental approach that makes it possible to accurately compute the timetable of laminar histogenesis from birthdating experiments. Here we report the results of an exhaustive examination of the tempo of layer production in five cortical areas of the mouse. Tritiated thymidine pulse injections were made during embryonic development and labeled neurons were examined in three frontoparietal areas (areas 3, 4, and 6) and two occipital areas (areas 17 and 18a) of the adult cortex. The correlation between the radial distribution of neurons and the intensities of labeling enabled us to reliably identify first generation neurons (i.e., those neurons that quit the cell-cycle in the first round of mitosis after injection). For each cortical layer, the percentage of first generation neurons with respect to the total number of neurons defined a laminar labeling index. Changes of the laminar labeling index over time determined the timetable of layer formation. The onset and duration of layer formation was identical in the two occipital areas. This finding contrasted with the frontoparietal areas where there were important differences in the timing of infragranular and granular layer formation and noticeably production of layers VIa, V, and IV occurs earlier in area 3 than in area 6. The timing of laminar production of areas 17 and 18a resembles more that of area 3 than that of area 6. With respect to areas 3 and 6, area 4 shows an intermediate but significantly different timetable of layer production. These marked areal differences in the timetable of laminar histogenesis contrasted with the relative homogeneity within areas so that we have been able to demonstrate that the interareal differences are not merely the expression of known neurogenic gradients. These results suggest that in the mouse frontoparietal Isocortex, neighbouring regions of the ventricular zone that will give rise to distinct areas follow distinct programs of layer production. These areal differences occur before thalamic innervation and suggest an early regionalisation of laminar histogenesis. J. Comp. Neurol. 385:95‐116, 1997. r 1997 Wiley-Liss, Inc. Indexing terms: tritiated thymidine; birthdating; cerebral cortex; regionalisation; cortical development
