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the cortical part of the neencephalon (同)neocortex

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/06/20 19:58:07」(JST)

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For other uses, see Neocortex (disambiguation).

The neocortex, (Latin for "new bark" or "new rind"), also called the neopallium ("new mantle") and isocortex ("equal rind"), is a part of the brain of mammals. It is the outer layer of the cerebral hemispheres, and made up of six layers, labelled I to VI (with VI being the innermost and I being the outermost). The neocortex is part of the cerebral cortex (along with the archicortex and paleocortex, which are cortical parts of the limbic system). In all mammals, it is involved in "higher functions" such as sensory perception, generation of motor commands, spatial reasoning, conscious thought and language.^[1]

Anatomy[edit]

The neocortex consists of the grey matter, or neuronal cell bodies and unmyelinated fibers, surrounding the deeper white matter (myelinated axons) in the cerebrum. The neocortex is smooth in rodents and other small mammals, whereas in primates and other larger mammals it has deep grooves (sulci) and wrinkles (gyri). These folds allow the surface area of the neocortex to increase far beyond what could otherwise be fit in the same size skull. All human brains have the same overall pattern of main gyri and sulci, although they differ in detail from one person to another. The mechanism by which the gyri form during embryogenesis is not entirely clear. However, it may be due to differences in cellular proliferation rates in different areas of the cortex early in embryonic development.^[2]

The neocortex contains two primary types of neurons, excitatory pyramidal neurons (~80% of neocortical neurons) and inhibitory interneurons (~20%). The structure of the neocortex is relatively uniform (hence the alternative names "iso-" and "homotypic" cortex), consisting of six horizontal layers segregated principally by cell type and neuronal connections. However, there are many exceptions to this uniformity; for example, the motor cortex lacks layer IV. There is some canonical circuitry within the cortex; for example, pyramidal neurons in the upper layers II and III project their axons to other areas of neocortex, while those in the deeper layers V and VI project primarily out of the cortex, e.g. to the thalamus, brainstem, and spinal cord. Neurons in layer IV receive all of the synaptic connections from outside the cortex (mostly from thalamus), and themselves make short-range, local connections to other cortical layers. Thus, layer IV receives all incoming sensory information and distributes it to the other layers for further processing.

The neurons of the neocortex are also arranged in vertical structures called neocortical columns. These are patches of the neocortex with a diameter of about 0.5 mm (and a depth of 2 mm). Each column typically responds to a sensory stimulus representing a certain body part or region of sound or vision. These columns are similar, and can be thought of as the basic repeating functional units of the neocortex. In humans, the neocortex consists of about a half-million of these columns, each of which contains approximately 70,000 neurons.^[3]

The neocortex is derived embryonically from the dorsal telencephalon, which is the rostral part of the forebrain. The neocortex is divided into frontal, parietal, occipital, and temporal lobes, which perform different functions. For example, the occipital lobe contains the primary visual cortex, and the temporal lobe contains the primary auditory cortex. Further subdivisions or areas of neocortex are responsible for more specific cognitive processes. In humans, the frontal lobe contains areas devoted to abilities that are enhanced in or unique to our species, such as complex language processing localized to the ventrolateral prefrontal cortex (Broca's area). In humans and other primates, social and emotional processing is localized to the orbitofrontal cortex. (See Cerebral cortex and Cerebrum.)

Evolution[edit]

The neocortex is the newest part of the cerebral cortex to evolve (hence the prefix "neo"); the other parts of the cerebral cortex are the paleocortex and archicortex, collectively known as the allocortex. The cellular organization of the allocortex is different from the six-layer structure mentioned above. In humans, 90% of the cerebral cortex is neocortex.

The six-layer cortex appears to be a distinguishing feature of mammals; it has been found in the brains of all mammals, but not in any other animals.^[1] There is some debate,^[4]^[5] however, as to the cross-species nomenclature for neocortex. In avians, for instance, there are clear examples of cognitive processes that are thought to be neocortical in nature, despite the lack of the distinctive six-layer neocortical structure.^[6] In a similar manner, reptiles, such as turtles, have primary sensory cortices. A consistent, alternative name has yet to be agreed upon.

Neocortex ratio[edit]

The neocortex ratio of a species is the ratio of the size of the neocortex to the rest of the brain. A high neocortex ratio is thought to correlate with a number of social variables such as group size and the complexity of social mating behaviors.^[7] (See Dunbar's number) Humans have a large neocortex as a percentage of total brain matter when compared with other mammals. For example, there is only a 30:1 ratio of neocortical gray matter to the size of the medulla in the brainstem of chimpanzees, while the ratio is 60:1 in humans.^[8]

References[edit]

^ ^a ^b Lui, J. H.; Hansen, D. V.; Kriegstein, A. R. (2011). "Development and Evolution of the Human Neocortex". Cell 146 (1): 18–36. doi:10.1016/j.cell.2011.06.030. PMC 3610574. PMID 21729779. edit
^ Ronan, L.; et al. (29 March 2013). "Differential Tangential Expansion as a Mechanism for Cortical Gyrification". Cereb. Cortex. doi:10.1093/cercor/bht082. PMID 23542881.
^ bluebrain.epfl.ch
^ Jarvis, Erich D.; Güntürkün, Onur; Bruce, Laura; Csillag, András; Karten, Harvey; Kuenzel, Wayne; Medina, Loreta; Paxinos, George et al. (2005). "Opinion: Avian brains and a new understanding of vertebrate brain evolution". Nature Reviews Neuroscience 6 (2): 151–9. doi:10.1038/nrn1606. PMC 2507884. PMID 15685220. |displayauthors= suggested (help)
^ Reiner, Anton; Perkel, David J.; Bruce, Laura L.; Butler, Ann B.; Csillag, András; Kuenzel, Wayne; Medina, Loreta; Paxinos, George et al. (2004). "Revised nomenclature for avian telencephalon and some related brainstem nuclei". The Journal of Comparative Neurology 473 (3): 377–414. doi:10.1002/cne.20118. PMC 2518311. PMID 15116397. |displayauthors= suggested (help)
^ Prior, Helmut; Schwarz, Ariane; Güntürkün, Onur (2008). "Mirror-Induced Behavior in the Magpie (Pica pica): Evidence of Self-Recognition". In De Waal, Frans. PLoS Biology 6 (8): e202. doi:10.1371/journal.pbio.0060202. PMC 2517622. PMID 18715117. Lay summary – New Scientist (August 19, 2008).
^ Dunbar, R.I.M. (1995). "Neocortex size and group size in primates: A test of the hypothesis". Journal of Human Evolution 28 (3): 287–96. doi:10.1006/jhev.1995.1021.
^ Semendeferi, K.; Lu, A.; Schenker, N.; Damasio, H. (2002). "Humans and great apes share a large frontal cortex". Nature Neuroscience 5 (3): 272–6. doi:10.1038/nn814. PMID 11850633.

English Journal

Theta oscillations orchestrate medial temporal lobe and neocortex in remembering autobiographical memories.

Fuentemilla L, Barnes GR, Düzel E, Levine B.Author information Cognition and Brain Plasticity Unit, Institute of Biomedical Research of Bellvitge (IDIBELL), L'Hospitalet, Barcelona, Spain; Department of Basic Psychology, University of Barcelona, Barcelona, Spain. Electronic address: lluis.fuentemilla@gmail.com.AbstractRemembering autobiographical events can be associated with detailed visual imagery. The medial temporal lobe (MTL), precuneus and prefrontal cortex are held to jointly enable such vivid retrieval, but how these regions are orchestrated remains unclear. An influential prediction from animal physiology is that neural oscillations in theta frequency may be important. In this experiment, participants prospectively collected audio recordings describing personal autobiographical episodes or semantic knowledge over 2 to 7months. These were replayed as memory retrieval cues while recording brain activity with magnetoencephalography (MEG). We identified a peak of theta power within a left MTL region of interest during both autobiographical and General Semantic retrieval. This MTL region was selectively phase-synchronized with theta oscillations in precuneus and medial prefrontal cortex, and this synchrony was higher during autobiographical as compared to General Semantic knowledge retrieval. Higher synchrony also predicted more detailed visual imagery during retrieval. Thus, theta phase-synchrony orchestrates in humans the MTL with a distributed neocortical memory network when vividly remembering autobiographical experiences.
NeuroImage.Neuroimage.2014 Jan 15;85 Pt 2:730-7. doi: 10.1016/j.neuroimage.2013.08.029. Epub 2013 Aug 23.
Remembering autobiographical events can be associated with detailed visual imagery. The medial temporal lobe (MTL), precuneus and prefrontal cortex are held to jointly enable such vivid retrieval, but how these regions are orchestrated remains unclear. An influential prediction from animal physiolog
PMID 23978597

Shifts in the vascular endothelial growth factor isoforms result in transcriptome changes correlated with early neural stem cell proliferation and differentiation in mouse forebrain.

Cain JT, Berosik MA, Snyder SD, Crawford NF, Nour SI, Schaubhut GJ, Darland DC.Author information Department of Biology, University of North Dakota, Grand Forks, North Dakota.AbstractRegulation of neural stem cell (NSC) fate decisions is critical during the transition from a multicellular mammalian forebrain neuroepithelium to the multilayered neocortex. Forebrain development requires coordinated vascular investment alongside NSC differentiation. Vascular endothelial growth factor A (Vegf) has proven to be a pleiotrophic gene whose multiple protein isoforms regulate a broad range of effects in neurovascular systems. To test the hypothesis that the Vegf isoforms (120, 164, and 188) are required for normal forebrain development, we analyzed the forebrain transcriptome of mice expressing specific Vegf isoforms, Vegf120, VegfF188, or a combination of Vegf120/188. Transcriptome analysis identified differentially expressed genes in embryonic day (E) 9.5 forebrain, a time point preceding dramatic neuroepithelial expansion and vascular investment in the telencephalon. Meta-analysis identified gene pathways linked to chromosome-level modifications, cell fate regulation, and neurogenesis that were altered in Vegf isoform mice. Based on these gene network shifts, we predicted that NSC populations would be affected in later stages of forebrain development. In the E11.5 telencephalon, we quantified mitotic cells [Phospho-Histone H3 (pHH3)-positive] and intermediate progenitor cells (Tbr2/Eomes-positive), observing quantitative and qualitative shifts in these populations. We observed qualitative shifts in cortical layering at P0, particularly with Ctip2-positive cells in layer V. The results identify a suite of genes and functional gene networks that can be used to further dissect the role of Vegf in regulating NSC differentiation and downstream consequences for NSC fate decisions. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 63-81, 2014.
Developmental neurobiology.Dev Neurobiol.2014 Jan;74(1):63-81. doi: 10.1002/dneu.22130. Epub 2013 Nov 4.
Regulation of neural stem cell (NSC) fate decisions is critical during the transition from a multicellular mammalian forebrain neuroepithelium to the multilayered neocortex. Forebrain development requires coordinated vascular investment alongside NSC differentiation. Vascular endothelial growth fact
PMID 24124161

How unique is the human neocortex?

Molnár Z, Pollen A.Author information Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK.AbstractThe human cerebral cortex is generally considered the most complex organ, and is the structure that we hold responsible for the repertoire of behavior that distinguishes us from our closest living and extinct relatives. At a recent Company of Biologists Workshop, 'Evolution of the Human Neocortex: How Unique Are We?' held in September 2013, researchers considered new information from the fields of developmental biology, genetics, genomics, molecular biology and ethology to understand unique features of the human cerebral cortex and their developmental and evolutionary origin.
Development (Cambridge, England).Development.2014 Jan;141(1):11-6. doi: 10.1242/dev.101279.
The human cerebral cortex is generally considered the most complex organ, and is the structure that we hold responsible for the repertoire of behavior that distinguishes us from our closest living and extinct relatives. At a recent Company of Biologists Workshop, 'Evolution of the Human Neocortex: H
PMID 24346696

Japanese Journal

Effects of Extracellular Matrix Macromolecules on the Differentiation of Plasma Membrane Structure in Cultured Astrocytes.

, , , ,
Cell Structure and Function 21(2), 133-141, 1996
… As an initial step to clarifying the totally unknown biochemical nature of this intramembrane structure, we have devised a culture system which enhances the differentiation of assemblies in secondary cultures of astrocytes derived from neonatal mouse neopallium. …
NAID 130003512932

胎生期ヒト脳，特にsecond trimesterの時期におけるMRIに関する研究

奈良医学雑誌 41(5), 593-614, 1990-10-31
… Magnetic resonance (MR) images were compared with histological and anatomical observations in 31 fetuses ranging from 10 to 25 weeks gestation to study the relationship between MR images and the development of the neopallium during the second trimester. … On T1 weighted MR images after 18 weeks gestation, the neopallium consisted of four layers which appeared as areas of high, relatively high, low and high signal intensity, respectively, from the ventricular side to the brain surface. …
NAID 80005706144

マウスのX線小頭症における脳血管形成異常について

亀山義郎,林靖,星野清
先天異常 : 日本先天異常学会会報 : official journal of Congeital Anomalies Research Association of Japan 12(3), 147-156, 1972-09-30
NAID 110002728059

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