Neocortex 487922 225706213 2008-07-15T00:24:24Z Bobo192 97951 Reverted edits by [[Special:Contributions/121.221.186.69|121.221.186.69]] ([[User talk:121.221.186.69|talk]]) to last version by DOI bot {{otheruses4|the region of the brain|the Crash Bandicoot villain|Doctor Neo Cortex}} {{Infobox Brain| Name = {{PAGENAME}} | Latin = | GraySubject = | GrayPage = | Image = | Caption = | Image2 = | Caption2 = | IsPartOf = | Components = | Artery = | Vein = | BrainInfoType = ancil | BrainInfoNumber = 754 | MeshName = Neocortex | MeshNumber = | DorlandsPre = n_03 | DorlandsSuf = 12561071 | }} The '''neocortex''' ([[Latin]] for "new [[bark]]" or "new [[rind]]") is a part of the [[brain]] of [[mammal]]s. It is the outer layer of the [[cerebral hemisphere]]s, 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]]). It is involved in higher functions such as [[sense|sensory perception]], generation of [[motor cortex|motor commands]], spatial reasoning, [[consciousness|conscious thought]] and, in humans, [[language]]. Other names for the neocortex include '''neopallium''' ("new [[fireplace mantel|mantel]]") and '''isocortex''' ("equal rind"). ==Anatomy== The neocortex consists of the [[grey matter]], or neuronal cell bodies and [[myelin|unmyelinated]] fibers, surrounding the deeper [[white matter]] ([[myelin|myelinated]] [[axons]]) in the [[cerebrum]]. Whereas the neocortex is smooth in [[rodents]] and other small mammals, it has deep grooves ([[sulcus (anatomy)|sulci]]) and wrinkles ([[gyrus|gyri]]) in [[primate]]s and other larger mammals. These folds increase the surface area of the neocortex considerably without taking up too much more volume. This has allowed primates and especially humans to evolve new functional areas of neocortex that are responsible for enhanced cognitive skills such as [[working memory]], speech, and language. 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 names "iso-" and "homotypic" cortex): it consists of six horizontal layers segregated principally by [[cell (biology)|cell]] type and [[neuron]]al 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 [[synapse|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 [[cortical column|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 [[Visual perception|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 60,000 neurons.{{Fact|date=December 2007}} The neocortex is divided into [[frontal lobe|frontal]], [[parietal lobe|parietal]], [[temporal lobe|temporal]], and [[occipital lobe|occipital]] 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]]) and social and emotional processing localized to the [[orbitofrontal cortex]]. (''See [[Cerebral cortex]] and [[Cerebrum]].'') The female human neocortex contains approximately 19 billion [[neurons]] while the male human neocortex has 23 billion.<ref>{{cite journal | author=Pakkenberg B, Gundersen HJ | title=Neocortical neuron number in humans: effect of sex and age | journal=J Comp Neurol | year=1997 Jul 28 | pages=312–20 | volume=384 | issue=2 | pmid=9215725 | doi=10.1002/(SICI)1096-9861(19970728)384:2<312::AID-CNE10>3.0.CO;2-K}}</ref> Additionally, the female neocortex has more white matter, while the male neocortex contains more grey matter. The implications of such differences are not fully known. ==Evolution== The neocortex is the newest part of the [[cerebral cortex]] to evolve (hence the name "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. There is some debate,<ref>{{cite journal | author=Jarvis ED, Gunturkun O, Bruce L, Csillag A, Karten H, Kuenzel W, Medina L, Paxinos G, Perkel DJ, Shimizu T, Striedter G, Wild JM, Ball GF, Dugas-Ford J, Durand SE, Hough GE, Husband S, Kubikova L, Lee DW, Mello CV, Powers A, Siang C, Smulders TV, Wada K, White SA, Yamamoto K, Yu J, Reiner A, Butler AB | title=Avian brains and a new understanding of vertebrate brain evolution | journal=Nat Rev Neurosci | year=2005 | pages=151–9 | volume=6 | issue=2 | pmid=15685220 | doi=10.1038/nrn1606}}</ref><ref>{{cite journal | author=Reiner A, Perkel DJ, Bruce LL, Butler AB, Csillag A, Kuenzel W, Medina L, Paxinos G, Shimizu T, Striedter G, Wild M, Ball GF, Durand S, Gunturkun O, Lee DW, Mello CV, Powers A, White SA, Hough G, Kubikova L, Smulders TV, Wada K, Dugas-Ford J, Husband S, Yamamoto K, Yu J, Siang C, Jarvis ED | title=Revised nomenclature for avian telencephalon and some related brainstem nuclei | journal=J Comp Neurol | year=2004 | pages=377–414 | volume=473 | issue=3 | pmid=15116397 | doi=10.1002/cne.20118}}</ref> however, as to the cross-[[species]] nomenclature for ''neocortex''. In [[bird|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. In a similar manner, [[reptile]]s, such as [[turtles]], have primary sensory cortices. A consistent, alternative name has yet to be agreed upon. ==Neocortex ratio== 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. ==See also== * [[List of regions in the human brain]] * [[Blue Brain]], a project to produce a computer simulation of a neocortical column and eventually a whole neocortex * Software model of the neocortex by Jeff Hawkins (http://www.numenta.com/) * Model of the neocortex by the Brain Engineering Laboratory at Dartmouth College (http://www.dartmouth.edu/~rhg/Research4Neo.html) *[[Dr. Neo Cortex]], a fictional character of the [[Crash Bandicoot]] series, whose name is based on the neocortex. ==References== <div class="references-small"><references /></div> [[Category:Neuroanatomy]] [[Category:Cerebrum]] [[ca:Neocòrtex]] [[da:Neokortex]] [[de:Neocortex]] [[es:Neocórtex]] [[fr:Néocortex]] [[nl:Neocortex]] [[no:Neocortex]] [[ja:大脳新皮質]] [[pt:Neocórtex]] [[ru:Новая кора]] [[sv:Neocortex]] [[zh:新皮质]]