cortical column

{{Main|Cerebral cortex}}

The mammalian cerebral cortex, the grey matter encapsulating the white matter, is composed of layers. The human cortex is between 2 and 3 mm thick.{{cite book |last1=Saladin |first1=Kenneth |title=Human anatomy |date=2011 |publisher=McGraw-Hill |isbn=9780071222075 |page=416 |edition=3rd}} The number of layers is the same in most mammals, but varies throughout the cortex. 6 layers can be recognized in the neocortex, although many regions lack one or more layers. For example, fewer layers are present in the archipallium and the paleopallium.{{cite book|author1=R Nieuwenhuys |author2=HJ Donkelaar |author3=C Nicholson |author4=WJAJ Smeets |author5=H Wicht |title=The central nervous system of vertebrates|year=1998|publisher=Springer|location=Berlin [u.a.]|isbn=978-3540560135}}

The columnar functional organization, as originally framed by Vernon Mountcastle, suggests that neurons that are horizontally more than 0.5 mm (500 μm) from each other do not have overlapping sensory receptive fields, and other experiments give similar results: 200–800 μm.{{cite journal |vauthors=Hubel DH, Wiesel TN, Stryker MP|title=Orientation columns in macaque monkey visual cortex demonstrated by the 2-deoxyglucose autoradiographic technique |journal=Nature |volume=269 |issue=5626 |pages=328–30 |date=September 1977 |pmid=409953|bibcode=1977Natur.269..328H |doi=10.1038/269328a0 |s2cid=4246375 }}{{cite journal |author=Leise EM |title=Modular construction of nervous systems: a basic principle of design for invertebrates and vertebrates |journal=Brain Research. Brain Research Reviews |volume=15 |issue=1 |pages=1–23 |year=1990 |pmid=2194614 |doi=10.1016/0165-0173(90)90009-d|s2cid=4996690 |url=http://libres.uncg.edu/ir/uncg/f/E_Leise_Modular_1990.pdf }} Various estimates suggest there are 50 to 100 cortical minicolumns in a hypercolumn, each comprising around 80 neurons. Their role is best understood as 'functional units of information processing.'

An important distinction is that the columnar organization is functional by definition, and reflects the local connectivity of the cerebral cortex. Connections "up" and "down" within the thickness of the cortex are much denser than connections that spread from side to side.

David Hubel and Torsten Wiesel followed up on Mountcastle's discoveries in the somatic sensory cortex with their own studies in vision. A part of the discoveries that resulted in them winning the 1981 Nobel Prize{{cite web |url=http://nobelprize.org/medicine/laureates/1981/ |title=The Nobel Prize in Medicine 1981 |accessdate=2008-04-13}} was that there were cortical columns in vision as well, and that the neighboring columns were also related in function in terms of the orientation of lines that evoked the maximal discharge. Hubel and Wiesel followed up on their own studies with work demonstrating the impact of environmental changes on cortical organization, and the sum total of these works resulted in their Nobel Prize.

There are about 200 million (2×10⁸) cortical minicolumns in the human neocortex with up to about 110 neurons each,{{cite journal | last1 = Krueger | first1 = James M. |display-authors=et al | year = 2008 | title = Sleep as a fundamental property of neuronal assemblies | journal = Nature Reviews Neuroscience | volume = 9 | issue = 12| pages = 910–919 | pmc=2586424 | pmid=18985047 | doi=10.1038/nrn2521}} and with estimates of 21–26 billion (2.1×10¹⁰–2.6×10¹⁰) neurons in the neocortex. With 50 to 100 cortical minicolumns per cortical column a human would have 2–4 million (2×10⁶–4×10⁶) cortical columns. There may be more if the columns can overlap, as suggested by Tsunoda et al.{{cite journal |author1=Kazushige Tsunoda |author2=Yukako Yamane |author3=Makoto Nishizaki |author4=Manabu Tanifuji |title=Complex objects are represented in macaque inferotemporal cortex by the combination of feature columns |journal=Nat. Neurosci. |volume=4 |issue=8 |pages=832–838 |date=August 2001 |pmid=11477430 |doi=10.1038/90547|s2cid=14714957 }} Jeff Hawkins claims that there are only 150,000 columns in the human neocortex, based on research made by his company Numenta.{{cite book |last1=Hawkins |first1=Jeff |title=A Thousand Brains: A New Theory of Intelligence |year=2021 |publisher=Basic Books |isbn=978-1541675810 |url=https://www.numenta.com/resources/books/a-thousand-brains-by-jeff-hawkins/ |access-date=23 January 2023}}

There are claims that minicolumns may have as many as 400 principal cells,{{cite book|title=Brain Mapping – An Encyclopedic Reference|editor=Arthur W. Toga|chapter=Acquisition Methods, Methods and Modeling|author=O. David, in Brain Mapping|year=2015|isbn=9780123973160}} but it is not clear if that includes glia cells.

Some contradict the previous estimates,{{Cite journal|last1=Powell|first1=T. P.|last2=Hiorns|first2=R. W.|last3=Rockel|first3=A. J.|date=June 1980|title=The basic uniformity in structure of the neocortex.|journal=Brain: A Journal of Neurology|volume=103|issue=2|pages=221–244|doi=10.1093/brain/103.2.221|issn=0006-8950|pmid=6772266}} claiming the original research is too arbitrary.{{Cite journal|last=Rakic|first=Pasko|date=2008-08-26|title=Confusing cortical columns|journal=Proceedings of the National Academy of Sciences|volume=105|issue=34|pages=12099–12100|doi=10.1073/pnas.0807271105|issn=0027-8424|pmid=18715998|pmc=2527871|bibcode=2008PNAS..10512099R|doi-access=free}} The authors propose a uniform neocortex, and choose a fixed width and length to calculate the cell numbers. Later research pointed out that the neocortex is indeed not uniform for other species,{{Cite journal|last1=Lent|first1=Roberto|last2=Kaas|first2=Jon H.|last3=Wong|first3=Peiyan|last4=Collins|first4=Christine E.|last5=Herculano-Houzel|first5=Suzana|date=2008-08-26|title=The basic nonuniformity of the cerebral cortex|journal=Proceedings of the National Academy of Sciences|volume=105|issue=34|pages=12593–12598|doi=10.1073/pnas.0805417105|issn=0027-8424|pmid=18689685|pmc=2527956|doi-access=free}} and studying nine primate species they found that "the number of neurons underneath 1 mm² of the cerebral cortical surface ... varies by three times across species." The neocortex is not uniform across species.{{Cite journal|last1=Lent|first1=Roberto|last2=Azevedo|first2=Frederico A. C.|last3=Andrade-Moraes|first3=Carlos H.|last4=Pinto|first4=Ana V. O.|date=2012|title=How many neurons do you have? Some dogmas of quantitative neuroscience under revision|journal=European Journal of Neuroscience|volume=35|issue=1|pages=1–9|doi=10.1111/j.1460-9568.2011.07923.x|pmid=22151227|s2cid=20365568|issn=1460-9568}}{{Cite journal|title=Chapter 7 - Cortical Columns|pages=109–129|last=Molnár|first=Z.|date=January 2013|journal=Neural Circuit Development and Function in the Brain|doi=10.1016/B978-0-12-397267-5.00137-0|isbn=9780123972675 }} The actual number of neurons within a single column is variable, and depends on the cerebral areas and thus the function of the column.

• Cortical minicolumn
• Ocular dominance column
• Predictive coding
• Radial unit hypothesis

{{Reflist}}

• {{Cite news |url=https://www.newscientist.com/article/dn7470-mission-to-build-a-simulated-brain-begins/ |title=Mission to build a simulated brain begins |date=6 June 2005 |first=Duncan |last=Graham-Rowe |work=New Scientist |quote=[...] the initial phase of Blue Brain will model the electrical structure of neocortical columns - neural circuits that are repeated throughout the brain. These are the network units of the brain, says Markram. Measuring just 0.5 millimetres by 2 mm, these units contain between 10 and 70,000 neurons, depending upon the species. Once this is complete, the behaviour of columns can be mapped and modelled [...]}}
• The Blue Brain Project aims to [https://web.archive.org/web/20080520020935/http://bluebrain.epfl.ch/page19092.html simulate a cortical column]
• On Intelligence—a popular science book about column function by Jeff Hawkins
• {{Cite journal

| last1 = Rakic | first1 = P.

| title = Confusing cortical columns

| doi = 10.1073/pnas.0807271105

| journal = Proceedings of the National Academy of Sciences

| volume = 105

| issue = 34

| pages = 12099–12100

|date=August 2008

| bibcode = 2008PNAS..10512099R

| pmid=18715998

| pmc=2527871

| doi-access = free

}} Summarizes what is known and corrects some misconceptions.

{{DEFAULTSORT:Cortical Column}}

Category:Neural circuitry