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Spontaneous symmetry breaking and the formation of columnar structures in the primary visual cortex II --- Local organization of orientation modules  [PDF]
Kengo Yamagishi
Physics , 1996,
Abstract: Self-organization of orientation-wheels observed in the visual cortex is discussed from the view point of topology. We argue in a generalized model of Kohonen's feature mappings that the existence of the orientation-wheels is a consequence of Riemann-Hurwitz formula from topology. In the same line, we estimate partition function of the model, and show that regardless of the total number N of the orientation-modules per hypercolumn the modules are self-organized, without fine-tuning of parameters, into definite number of orientation-wheels per hypercolumn if N is large.
SOBRE LA ORGANIZACIóN COLUMNAR DE LA CORTEZA CEREBRAL ON THE COLUMNAR ORGANIZATION OF THE CEREBRAL CORTEZ
Gabriel Arteaga D,Hernán José Pimienta J
Revista Colombiana de Psiquiatría , 2004,
Abstract: En el presente trabajo se exponen, de manera sucinta, las dos principales formas de organización estructural de la corteza cerebral de los mamíferos, especialmente de los primates superiores: las denominadas organización horizontal y organización vertical, aunque se hace hincapié en esta última. El patrón de organización vertical se refiere a la disposición en 'láminas' paralelas a la superficie cortical, mientras que el patrón de organización vertical describe agrupamientos celulares, ortogonales a la superficie cortical, los cuales han recibido el nombre de columnas o módulos y han sido propuestos, por diversos autores, como la unidad mínima de procesamiento de la corteza cerebral y base de postulados psicobiológicos contemporáneos. Se presentan algunos antecedentes relevantes para el concepto de columna cortical, especialmente la documentación experimental obtenida en las cortezas sensoriales, motoras y de asociación. De igual manera, se consideran los componentes celulares, asociados con la organización de las columnas corticales. Finalmente, se describen las características de la conectividad específica, de algunas de las mejor conocidas interneuronas de la corteza cerebral. This paper exposes succinctly the two main tendencies in the structural organization of the mammalian cerebral cortex, particularly that of superior primates: the so called "horizontal organization" and the "vertical organization", with an emphasis on the latter. The horizontal pattern of organization refers to the arrangement in "layers" that run parallel to the cortical surface, whereas the vertical pattern describes clusters of cells orthogonal to the cerebral surface called "columns" or "modules", those arrangements have been proposed as the "minimal processing unit" in the cerebral cortex and constitute the basis of contemporary psychobiological postulates. Relevant background to the concept of column is presented, particularly the experimental data found in the sensorial, motor and associative cortex. Cellular components associated with the structure of the cortical columns are considered. Finally the specific connectivity of some of the best known interneurons of the cerebral cortex is described.
The role of reelin in the development and evolution of the cerebral cortex
Tissir, F.;Lambert de Rouvroit, C.;Goffinet, A.M.;
Brazilian Journal of Medical and Biological Research , 2002, DOI: 10.1590/S0100-879X2002001200007
Abstract: reelin is an extracellular matrix protein that is defective in reeler mutant mice and plays a key role in the organization of architectonic patterns, particularly in the cerebral cortex. in mammals, a "reelin signal" is activated when reelin, secreted by cajal-retzius neurons, binds to receptors of the lipoprotein receptor family on the surface of cortical plate cells, and triggers dab1 phosphorylation. as reelin is a key component of cortical development in mammals, comparative embryological studies of reelin expression were carried out during cortical development in non-mammalian amniotes (turtles, squamates, birds and crocodiles) in order to assess the putative role of reelin during cortical evolution. the data show that reelin is present in the cortical marginal zone in all amniotes, and suggest that reelin has been implicated in the evolution of the radial organization of the cortical plate in the synapsid lineage leading from stem amniotes to mammals, as well as in the lineage leading to squamates, thus providing an example of homoplastic evolution (evolutionary convergence). the mechanisms by which reelin instructs radial cortical organization in these two lineages seem different: in the synapsid lineage, a drastic amplification of reelin production occurred in cajal-retzius cells, whereas in squamates, in addition to reelin-secreting cells in the marginal zone, a second layer of reelin-producing cells developed in the subcortex. altogether, our results suggest that the reelin-signaling pathway has played a significant role in shaping the evolution of cortical development.
The role of reelin in the development and evolution of the cerebral cortex  [cached]
Tissir F.,Lambert de Rouvroit C.,Goffinet A.M.
Brazilian Journal of Medical and Biological Research , 2002,
Abstract: Reelin is an extracellular matrix protein that is defective in reeler mutant mice and plays a key role in the organization of architectonic patterns, particularly in the cerebral cortex. In mammals, a "reelin signal" is activated when reelin, secreted by Cajal-Retzius neurons, binds to receptors of the lipoprotein receptor family on the surface of cortical plate cells, and triggers Dab1 phosphorylation. As reelin is a key component of cortical development in mammals, comparative embryological studies of reelin expression were carried out during cortical development in non-mammalian amniotes (turtles, squamates, birds and crocodiles) in order to assess the putative role of reelin during cortical evolution. The data show that reelin is present in the cortical marginal zone in all amniotes, and suggest that reelin has been implicated in the evolution of the radial organization of the cortical plate in the synapsid lineage leading from stem amniotes to mammals, as well as in the lineage leading to squamates, thus providing an example of homoplastic evolution (evolutionary convergence). The mechanisms by which reelin instructs radial cortical organization in these two lineages seem different: in the synapsid lineage, a drastic amplification of reelin production occurred in Cajal-Retzius cells, whereas in squamates, in addition to reelin-secreting cells in the marginal zone, a second layer of reelin-producing cells developed in the subcortex. Altogether, our results suggest that the reelin-signaling pathway has played a significant role in shaping the evolution of cortical development.
Reorganization of columnar architecture in the growing visual cortex  [PDF]
Wolfgang Keil,Karl-Friedrich Schmidt,Siegrid Loewel,Matthias Kaschube
Quantitative Biology , 2009, DOI: 10.1073/pnas.0913020107
Abstract: Many cortical areas increase in size considerably during postnatal development, progressively displacing neuronal cell bodies from each other. At present, little is known about how cortical growth affects the development of neuronal circuits. Here, in acute and chronic experiments, we study the layout of ocular dominance (OD) columns in cat primary visual cortex (V1) during a period of substantial postnatal growth. We find that despite a considerable size increase of V1, the spacing between columns is largely preserved. In contrast, their spatial arrangement changes systematically over this period. While in young animals columns are more band-like, layouts become more isotropic in mature animals. We propose a novel mechanism of growth-induced reorganization that is based on the `zigzag instability', a dynamical instability observed in several inanimate pattern forming systems. We argue that this mechanism is inherent to a wide class of models for the activity-dependent formation of OD columns. Analyzing one member of this class, the Elastic Network model, we show that this mechanism can account for the preservation of column spacing and the specific mode of reorganization of OD columns that we observe. We conclude that neurons systematically shift their selectivities during normal development and that this reorganization is induced by the cortical expansion during growth. Our work suggests that cortical circuits remain plastic for an extended period in development in order to facilitate the modification of neuronal circuits to adjust for cortical growth.
From Modular to Centralized Organization of Synchronization in Functional Areas of the Cat Cerebral Cortex  [PDF]
Jesús Gómez-Garde?es,Gorka Zamora-López,Yamir Moreno,Alex Arenas
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012313
Abstract: Recent studies have pointed out the importance of transient synchronization between widely distributed neural assemblies to understand conscious perception. These neural assemblies form intricate networks of neurons and synapses whose detailed map for mammals is still unknown and far from our experimental capabilities. Only in a few cases, for example the C. elegans, we know the complete mapping of the neuronal tissue or its mesoscopic level of description provided by cortical areas. Here we study the process of transient and global synchronization using a simple model of phase-coupled oscillators assigned to cortical areas in the cerebral cat cortex. Our results highlight the impact of the topological connectivity in the developing of synchronization, revealing a transition in the synchronization organization that goes from a modular decentralized coherence to a centralized synchronized regime controlled by a few cortical areas forming a Rich-Club connectivity pattern.
Rich Club Organization of Macaque Cerebral Cortex and Its Role in Network Communication  [PDF]
Logan Harriger, Martijn P. van den Heuvel, Olaf Sporns
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046497
Abstract: Graph-theoretical analysis of brain connectivity data has revealed significant features of brain network organization across a range of species. Consistently, large-scale anatomical networks exhibit highly nonrandom attributes including an efficient small world modular architecture, with distinct network communities that are interlinked by hub regions. The functional importance of hubs motivates a closer examination of their mutual interconnections, specifically to examine the hypothesis that hub regions are more densely linked than expected based on their degree alone, i.e. forming a central rich club. Extending recent findings of rich club topology in the cat and human brain, this report presents evidence for the existence of rich club organization in the cerebral cortex of a non-human primate, the macaque monkey, based on a connectivity data set representing a collation of numerous tract tracing studies. Rich club regions comprise portions of prefrontal, parietal, temporal and insular cortex and are widely distributed across network communities. An analysis of network motifs reveals that rich club regions tend to form star-like configurations, indicative of their central embedding within sets of nodes. In addition, rich club nodes and edges participate in a large number of short paths across the network, and thus contribute disproportionately to global communication. As rich club regions tend to attract and disperse communication paths, many of the paths follow a characteristic pattern of first increasing and then decreasing node degree. Finally, the existence of non-reciprocal projections imposes a net directional flow of paths into and out of the rich club, with some regions preferentially attracting and others dispersing signals. Overall, the demonstration of rich club organization in a non-human primate contributes to our understanding of the network principles underlying neural connectivity in the mammalian brain, and further supports the hypothesis that rich club regions and connections have a central role in global brain communication.
SOBRE LA ORGANIZACIóN COLUMNAR DE LA CORTEZA CEREBRAL
Arteaga D,Gabriel; Pimienta J,Hernán José;
Revista Colombiana de Psiquiatría , 2004,
Abstract: this paper exposes succinctly the two main tendencies in the structural organization of the mammalian cerebral cortex, particularly that of superior primates: the so called "horizontal organization" and the "vertical organization", with an emphasis on the latter. the horizontal pattern of organization refers to the arrangement in "layers" that run parallel to the cortical surface, whereas the vertical pattern describes clusters of cells orthogonal to the cerebral surface called "columns" or "modules", those arrangements have been proposed as the "minimal processing unit" in the cerebral cortex and constitute the basis of contemporary psychobiological postulates. relevant background to the concept of column is presented, particularly the experimental data found in the sensorial, motor and associative cortex. cellular components associated with the structure of the cortical columns are considered. finally the specific connectivity of some of the best known interneurons of the cerebral cortex is described.
Lack of tonotopic organization of the auditory cortex in schizophrenia  [PDF]
Thomas Ragole,Erin Slason,Peter Teale,Martin Reite,Donald C. Rojas
PeerJ , 2015, DOI: 10.7287/peerj.preprints.226v1
Abstract: Background: Disorganization of tonotopy in the auditory cortex has been described in schizophrenia. Subjects with schizophrenia show little to no spatial organization of responses to different tone frequencies in the auditory cortex. Previous studies have called into question the use of MEG and the M100 response to assess tonotopy. This study seeks to replicate prior results of tonotopic disorganization in schizophrenia compared to healthy controls.
A unified framework for the organization of the primate auditory cortex  [PDF]
Simon Baumann,Christopher I. Petkov,Timothy D. Griffiths
Frontiers in Systems Neuroscience , 2013, DOI: 10.3389/fnsys.2013.00011
Abstract: In non-human primates a scheme for the organization of the auditory cortex is frequently used to localize auditory processes. The scheme allows a common basis for comparison of functional organization across non-human primate species. However, although a body of functional and structural data in non-human primates supports an accepted scheme of nearly a dozen neighboring functional areas, can this scheme be directly applied to humans? Attempts to expand the scheme of auditory cortical fields in humans have been severely hampered by a recent controversy about the organization of tonotopic maps in humans, centered on two different models with radically different organization. We point out observations that reconcile the previous models and suggest a distinct model in which the human cortical organization is much more like that of other primates. This unified framework allows a more robust and detailed comparison of auditory cortex organization across primate species including humans.
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