Editing Neocortex

{{short description|Mammalian structure involved in higher-order brain functions}}
{{About|the mammalian brain structure}}
{{Infobox Brain
|Name            = Neocortex
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|Caption         = A representative [[cortical column|column]] of neocortex. Cell body layers are labeled on the left, and fiber layers are labeled on the right.
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The '''neocortex''', also called the '''neopallium''', '''isocortex''', or the '''six-layered cortex''', is a set of layers of the [[mammalian]] [[cerebral cortex]] involved in higher-order brain functions such as [[sense|sensory perception]], cognition, generation of [[motor cortex|motor commands]],<ref>{{cite journal | vauthors = Lodato S, Arlotta P | title = Generating neuronal diversity in the mammalian cerebral cortex | journal = Annual Review of Cell and Developmental Biology | volume = 31 | issue = 1 | pages = 699–720 | date = 2015-11-13 | pmid = 26359774 | pmc = 4778709 | doi = 10.1146/annurev-cellbio-100814-125353 | quote = The neocortex is the part of the brain responsible for execution of higher-order brain functions, including cognition, sensory perception, and sophisticated motor control. }}</ref> [[Spatial visualization ability|spatial reasoning]], and [[language]].<ref name="Lui 2011">{{cite journal | vauthors = Lui JH, Hansen DV, Kriegstein AR | title = Development and evolution of the human neocortex | journal = Cell | volume = 146 | issue = 1 | pages = 18–36 | date = July 2011 | pmid = 21729779 | pmc = 3610574 | doi = 10.1016/j.cell.2011.06.030 }}</ref> The neocortex is further subdivided into the '''true isocortex''' and the [[proisocortex]].<ref>{{cite web|title=BrainInfo|url=http://braininfo.rprc.washington.edu/centraldirectory.aspx?ID=2311|website=braininfo.rprc.washington.edu}}</ref>

In the [[human brain]], the [[cerebral cortex]] consists of the larger neocortex and the smaller [[allocortex]], respectively taking up 90% and 10%.<ref>{{cite book |last1=Saladin |first1=K |title=Anatomy & physiology : the unity of form and function |date=2012 |publisher=McGraw-Hill |location=New York, NY |isbn=9780073378251 |pages=417 |edition=6th}}</ref> The neocortex is made up of [[Cortical layers|six layers]], labelled from the outermost inwards, I to VI.

== Etymology == 
The term is from ''cortex'', [[Latin]], "[[Bark (botany)|bark]]" or "rind", combined with ''neo-'', [[Greek (language)|Greek]], "new". ''Neopallium'' is a similar hybrid, from Latin ''pallium'', "cloak". ''Isocortex'' and ''allocortex'' are hybrids with Greek ''isos'', "same", and ''allos'', "other".

==Anatomy==
The neocortex is the most developed in its organisation and number of layers, of the cerebral tissues.<ref>{{cite book |title=Dorland's Illustrated Medical Dictionary|date=2012|publisher=Elsevier Saunders|isbn=978-1-4160-6257-8|page=1238|edition=32nd}}</ref> The neocortex consists of the [[grey matter]], or neuronal cell bodies and [[myelin|unmyelinated]] fibers, surrounding the deeper [[white matter]] ([[myelin]]ated [[axon]]s) in the [[cerebrum]]. This is a very thin layer though, about 2–4&nbsp;mm thick.<ref>{{cite book|last1=Kandel|first1=Eric | name-list-style = vanc |title=Principles of neural science|date=2006|publisher=McGraw Hill|location=Appleton and Lange|isbn=978-0071390118|edition=5th}}</ref> There are two types of cortex in the neocortex, the [[proisocortex]] and the true isocortex. The pro-isocortex is a transitional area between the true isocortex and the [[periallocortex]] (part of the [[allocortex]]). It is found in the [[cingulate cortex]] (part of the [[limbic system]]), in [[Brodmann area|Brodmann's area]]s [[Brodmann area 24|24]], [[Brodmann area 25|25]], [[Brodmann area 30|30]] and [[Brodmann area 32|32]], the [[Insular cortex|insula]] and the [[parahippocampal gyrus]].

Of all the mammals studied to date (including humans), a species of [[oceanic dolphin]] known as the [[long-finned pilot whale]] has been found to have the most neocortical neurons.<ref>{{cite journal | vauthors = Mortensen HS, Pakkenberg B, Dam M, Dietz R, Sonne C, Mikkelsen B, Eriksen N | title = Quantitative relationships in delphinid neocortex | journal = Frontiers in Neuroanatomy | volume = 8 | pages = 132 | year = 2014 | pmid = 25505387 | pmc = 4244864 | doi = 10.3389/fnana.2014.00132 | doi-access = free }}</ref>

===Geometry===

The neocortex is smooth in [[rodent]]s and other small mammals, whereas in [[elephant]]s, [[dolphins]] and [[primate]]s and other larger mammals it has deep grooves ([[sulcus (neuroanatomy)|sulci]]) and ridges ([[gyrus|gyri]]). These folds allow the surface area of the neocortex to be greatly increased. All human brains have the same overall pattern of main gyri and sulci, although they differ in detail from one person to another.<ref name="Moerel,2006">{{cite journal | vauthors = Moerel M, De Martino F, Formisano E |title = An anatomical and functional topography of human auditory cortical areas. |journal = Front. Neurosci. |volume = 8 |issue = 225 |pages =  225|date = 2006 |pmid =  25120426|pmc = 4114190 |doi =  10.3389/fnins.2014.00225|quote = For example, in the human brain, the auditory cortex presents an expansion of cortical surface, with additional gyri and with a much larger inter-individual variability...|doi-access = free }}</ref> The mechanism by which the gyri form during embryogenesis is not entirely clear, and there are several competing hypotheses that explain gyrification, such as axonal tension,<ref name="Van Essen 1997">{{cite journal | vauthors = Van Essen DC | title = A tension-based theory of morphogenesis and compact wiring in the central nervous system | journal = Nature | volume = 385 | issue = 6614 | pages = 313–8 | date = January 1997 | pmid = 9002514 | doi = 10.1038/385313a0 | s2cid = 4355025 | url = http://person.hst.aau.dk/06gr1088d/artikler/Pdf/A%20tension-based%20theory%20of%20morphogenesis%20and%20compact%20wiring%20in%20the%20central%20nervous%20system.pdf }}</ref> cortical buckling<ref name="Richman 1975">{{cite journal | vauthors = Richman DP, Stewart RM, Hutchinson JW, Caviness VS | title = Mechanical model of brain convolutional development | journal = Science | volume = 189 | issue = 4196 | pages = 18–21 | date = July 1975 | pmid = 1135626 | doi = 10.1126/science.1135626 }}</ref> or differences in cellular proliferation rates in different areas of the cortex.<ref name="Ronan 2013">{{cite journal | vauthors = Ronan L, Voets N, Rua C, Alexander-Bloch A, Hough M, Mackay C, Crow TJ, James A, Giedd JN, Fletcher PC | title = Differential tangential expansion as a mechanism for cortical gyrification | journal = Cerebral Cortex | volume = 24 | issue = 8 | pages = 2219–28 | date = August 2014 | pmid = 23542881 | pmc = 4089386 | doi = 10.1093/cercor/bht082 | url = }}</ref>

===Layers===
[[File:Layers of the neocortex.png|thumb|555x555px|Neurons form distinct layers in mouse visual cortex.  Layer II/III (green), Layer IV (purple), Layer V (red), Layer VI (yellow). 3D reconstructions from the MICrONS cubic millimeter. ]]
The neocortex contains both excitatory (~80%) and inhibitory (~20%) [[neurons]], named for their effect on other neurons.<ref name="Noback; Strominger; Demarest; Ruggiero 2005">{{cite book|vauthors=Noback CR, Strominger NL, Demarest RJ, Ruggiero DA|title=The Human Nervous System: Structure and Function|date=2005|publisher=Humana Press|location=Totowa, NJ|isbn=1-59259-730-0|edition=Sixth}}</ref> The human neocortex consists of hundreds of different types of cells.<ref>{{Cite journal |last1=Berg |first1=Jim |last2=Sorensen |first2=Staci A. |last3=Ting |first3=Jonathan T. |last4=Miller |first4=Jeremy A. |last5=Chartrand |first5=Thomas |last6=Buchin |first6=Anatoly |last7=Bakken |first7=Trygve E. |last8=Budzillo |first8=Agata |last9=Dee |first9=Nick |last10=Ding |first10=Song-Lin |last11=Gouwens |first11=Nathan W. |last12=Hodge |first12=Rebecca D. |last13=Kalmbach |first13=Brian |last14=Lee |first14=Changkyu |last15=Lee |first15=Brian R. |date=October 2021 |title=Human neocortical expansion involves glutamatergic neuron diversification |journal=Nature |language=en |volume=598 |issue=7879 |pages=151–158 |doi=10.1038/s41586-021-03813-8 |pmid=34616067 |pmc=8494638 |issn=1476-4687|doi-access=free }}</ref> 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 (biology)|cell]] type and [[neuron]]al connections.<ref>{{Cite book|title = How to Create a Mind: The Secret of Human Thought Revealed|last = Kurzweil|first = Ray | name-list-style = vanc |publisher = Viking Penguin|year = 2012|isbn = 978-0670025299|location = New York|pages = 36}}</ref> However, there are many exceptions to this uniformity; for example, layer IV is small or missing in the [[motor cortex|primary motor cortex]]. 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 often project out of the cortex, e.g. to the [[thalamus]], [[brainstem]], and [[spinal cord]]. Neurons in layer IV receive the majority of the [[synapse|synaptic connections]] from outside the cortex (mostly from thalamus), and themselves make short-range, local connections to other cortical layers.<ref name="Noback; Strominger; Demarest; Ruggiero 2005"/> Thus, layer IV is the main recipient of incoming sensory information and distributes it to the other layers for further processing.

===Cortical columns===
[[File:Cortical Minicolumn.png|thumb|315x315px|The column is often thought of as the basic repeating functional unit of the neocortex. Neurons are color-coded by their layer: Layer II/III (green), Layer IV (purple), Layer V (red), Layer VI (yellow). ]]
The neocortex is often described as being arranged in vertical structures called [[cortical columns]], patches of neocortex with a diameter of roughly 0.5&nbsp;mm (and a depth of 2&nbsp;mm, i.e., spanning all six layers). These columns are often thought of as the basic repeating functional units of the neocortex, but their many definitions, in terms of anatomy, size, or function, are generally not consistent with each other, leading to a lack of consensus regarding their structure or function or even whether it makes sense to try to understand the neocortex in terms of columns.<ref name="Horton 2005">{{cite journal | vauthors = Horton JC, Adams DL | title = The cortical column: a structure without a function | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 360 | issue = 1456 | pages = 837–62 | date = April 2005 | pmid = 15937015 | pmc = 1569491 | doi = 10.1098/rstb.2005.1623 }}</ref>

== Function ==
The neocortex is derived embryonically from the dorsal [[telencephalon]], which is the [[Anatomical terms of location#Directional terms|rostral]] part of the [[Prosencephalon|forebrain]]. The neocortex is divided into regions demarcated by the cranial sutures in the skull above, into [[frontal lobe|frontal]], [[parietal lobe|parietal]], [[occipital lobe|occipital]], and [[temporal lobe|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]]).<ref name="Noback; Strominger; Demarest; Ruggiero 2005"/> In humans and other primates, social and emotional processing is localized to the [[orbitofrontal cortex]].

The neocortex has also been shown to play an influential role in sleep, memory and learning processes. [[Semantic memories]] appear to be stored in the neocortex, specifically the anterolateral [[temporal lobe]] of the neocortex.<ref name="Carlson 2013">{{cite book|last=Carlson|first=Neil | name-list-style = vanc |title=Physiology of Psychology|date=2013|publisher=Pearson|isbn=978-0-205-239481|edition=Eleventh}}</ref> It is also involved in [[instrumental conditioning]]; responsible for transmitting sensory information and information about plans for movement to the [[basal ganglia]].<ref name="Carlson 2013"/> The firing rate of neurons in the neocortex also has an effect on [[slow-wave sleep]]. When the neurons are at rest and are [[Hyperpolarization (biology)|hyperpolarizing]], a period of inhibition occurs during a slow [[oscillation]], called the down state. When the neurons of the neocortex are in the excitatory [[depolarizing]] phase and are firing briefly at a high rate, a period of excitation occurs during a slow oscillation, called the up state.<ref name="Carlson 2013"/>

==Clinical significance==
Lesions that develop in [[neurodegenerative disorders]], such as [[Alzheimer's disease]], interrupt the transfer of information from the sensory neocortex to the prefrontal neocortex. This disruption of sensory information contributes to the progressive symptoms seen in neurodegenerative disorders such as changes in personality, decline in cognitive abilities, and [[dementia]].<ref name="Pathological changes in the parahippocampal region in select non-Alzheimer's dementias">{{cite book|vauthors=Braak H, Del-Tredici K, Bohl J, Bratzke H, Braak E|title=Annals of the New York academy of sciences, Vol. 911.|date=2000|publisher=New York, NY, US: New York Academy of Sciences|isbn=1-57331-263-0}}</ref> Damage to the neocortex of the anterolateral temporal lobe results in [[semantic dementia]], which is the loss of memory of factual information ([[semantic memories]]). These symptoms can also be replicated by [[transcranial magnetic stimulation]] of this area. If damage is sustained to this area, patients do not develop [[anterograde amnesia]] and are able to recall [[Episodic memory|episodic information]].<ref>{{cite book|last=Carlson|first=Neil | name-list-style = vanc |title=Physiology of Behavior|date=2013|publisher=Pearson|isbn=978-0-205-23948-1}}</ref>

==Evolution==
{{See also|Pallium (neuroanatomy)#Evolution}}
The neocortex is the newest part of the [[cerebral cortex]] to evolve (hence the prefix ''neo'' meaning new); the other part of the cerebral cortex is the [[allocortex]]. The cellular organization of the allocortex is different from the six-layered neocortex. In humans, 90% of the cerebral cortex and 76% of the entire brain is neocortex.<ref name="Noback; Strominger; Demarest; Ruggiero 2005"/>

For a species to develop a larger neocortex, the brain must evolve in size so that it is large enough to support the region. Body size, basal [[metabolic rate]] and life history are factors affecting brain evolution and the [[coevolution]] of neocortex size and group size.<ref name="pmid17301028">{{cite journal | vauthors = Dunbar RI, Shultz S | title = Understanding primate brain evolution | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 362 | issue = 1480 | pages = 649–58 | date = April 2007 | pmid = 17301028 | pmc = 2346523 | doi = 10.1098/rstb.2006.2001 }}</ref> The neocortex increased in size in response to pressures for greater cooperation and competition in early ancestors. With the size increase, there was greater voluntary inhibitory control of social behaviors resulting in increased social harmony.<ref>{{cite book|vauthors=Bjorklund D, Kipp K|title=Social cognition, inhibition, and theory of mind: The evolution of human intelligence|date=2002|publisher=Lawrence Erlbaum Associate Publishers|location=Mahwah, NJ|isbn=0-8058-3267-X}}</ref>

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.<ref name="Lui 2011"/> There is some debate,<ref>{{cite journal | vauthors = Jarvis ED, Güntürkün 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 | display-authors = 6 | title = Avian brains and a new understanding of vertebrate brain evolution | journal = Nature Reviews. Neuroscience | volume = 6 | issue = 2 | pages = 151–9 | date = February 2005 | pmid = 15685220 | pmc = 2507884 | doi = 10.1038/nrn1606 | author30 = Avian Brain Nomenclature Consortium }}</ref><ref>{{cite journal | vauthors = 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, Güntürkün 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, Gütürkün 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, ((Avian Brain Nomenclature Forum)) | display-authors = 6 | title = Revised nomenclature for avian telencephalon and some related brainstem nuclei | journal = The Journal of Comparative Neurology | volume = 473 | issue = 3 | pages = 377–414 | date = May 2004 | pmid = 15116397 | pmc = 2518311 | 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.<ref>{{cite journal | vauthors = Prior H, Schwarz A, Güntürkün O | title = Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition | journal = PLOS Biology | volume = 6 | issue = 8 | pages = e202 | date = August 2008 | pmid = 18715117 | pmc = 2517622 | doi = 10.1371/journal.pbio.0060202 | editor1-first = Frans | editor1-last = De Waal | doi-access = free }}
*{{cite magazine |author=Alison Motluk |date=19 August 2008 |title=Mirror test shows magpies aren't so bird-brained |magazine=New Scientist |url=https://www.newscientist.com/article/dn14552-mirror-test-shows-magpies-arent-so-birdbrained.html |url-access=registration}}</ref> Evidence suggest the [[avian pallium]] to be broadly equivalent to the mammalian neocortex.<ref>{{Cite journal |last1=Stacho |first1=Martin |last2=Herold |first2=Christina |last3=Rook |first3=Noemi |last4=Wagner |first4=Hermann |last5=Axer |first5=Markus |last6=Amunts |first6=Katrin |last7=Güntürkün |first7=Onur |date=2020-09-25 |title=A cortex-like canonical circuit in the avian forebrain |url=https://www.science.org/doi/10.1126/science.abc5534 |journal=Science |language=en |volume=369 |issue=6511 |doi=10.1126/science.abc5534 |pmid=32973004 |issn=0036-8075|url-access=subscription }}</ref><ref>{{Cite journal |last1=Nieder |first1=Andreas |last2=Wagener |first2=Lysann |last3=Rinnert |first3=Paul |date=September 25, 2020 |title=A neural correlate of sensory consciousness in a corvid bird |url=https://www.science.org/doi/10.1126/science.abb1447 |journal=Science |language=en |volume=369 |issue=6511 |pages=1626–1629 |doi=10.1126/science.abb1447 |pmid=32973028 |bibcode=2020Sci...369.1626N |issn=0036-8075|url-access=subscription }}</ref><ref>{{Cite journal |last=Herculano-Houzel |first=Suzana |date=September 25, 2020 |title=Birds do have a brain cortex—and think |url=https://www.science.org/doi/10.1126/science.abe0536 |journal=Science |language=en |volume=369 |issue=6511 |pages=1567–1568 |doi=10.1126/science.abe0536 |pmid=32973020 |bibcode=2020Sci...369.1567H |issn=0036-8075|url-access=subscription }}</ref> In a similar manner, [[reptile]]s, such as [[turtle]]s, 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 [[Dunbar's number|group size]] and the complexity of social mating behaviors.<ref>{{cite journal |doi=10.1006/jhev.1995.1021 |title=Neocortex size and group size in primates: A test of the hypothesis |year=1995 | vauthors = Dunbar RI |journal=Journal of Human Evolution |volume=28 |issue=3 |pages=287–96}}</ref> 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 oblongata]] in the brainstem of chimpanzees, while the ratio is 60:1 in humans.<ref>{{cite journal | vauthors = Semendeferi K, Lu A, Schenker N, Damasio H | title = Humans and great apes share a large frontal cortex | journal = Nature Neuroscience | volume = 5 | issue = 3 | pages = 272–6 | date = March 2002 | pmid = 11850633 | doi = 10.1038/nn814 | s2cid = 5921065 }}</ref>

== 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
* [[Memory-prediction framework]], a theory of the neocortex function by Jeff Hawkins and related software models
* [[Claustrum]]

== References ==
{{reflist|2}}

== External links ==
* [[v:Comparative Neuroscience|Comparative Neuroscience]] at [[v:|Wikiversity]]
* {{cite web |url= http://www.dartmouth.edu/~rhg/Research4Neo.html |title= Model of the neocortex |work= Brain Engineering Laboratory |publisher= [[Dartmouth College]] }}
* {{cite web |url= http://braininfo.rprc.washington.edu/Scripts/ancilcentraldirectory.asp?ID=757 |title= Proisocortex |work= Brain Info |publisher= [[University of Washington]] |access-date= 2014-06-17 |archive-date= 2006-10-23 |archive-url= https://web.archive.org/web/20061023164133/http://braininfo.rprc.washington.edu/Scripts/ancilcentraldirectory.asp?ID=757 |url-status= dead }}

{{Cortex types}}

{{Authority control}}

[[Category:Cerebral cortex]]