Editing Neocortex (section)

==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>