Cortical column

A cortical column is a group of neurons forming a cylindrical structure through the cerebral cortex of the brain perpendicular to the cortical surface.[1] The structure was first identified by Mountcastle in 1957. He later identified minicolumns as the basic units of the neocortex which were arranged into columns.[2] Each contains the same types of neurons, connectivity, and firing properties.[3] Columns are also called hypercolumn, macrocolumn,[4] functional column[5] or sometimes cortical module.[6] Neurons within a minicolumn (microcolumn) encode similar features, whereas a hypercolumn "denotes a unit containing a full set of values for any given set of receptive field parameters".[7] A cortical module is defined as either synonymous with a hypercolumn (Mountcastle) or as a tissue block of multiple overlapping hypercolumns.[8]

Cortical columns are proposed to be the canonical microcircuits for predictive coding,[9] in which the process of cognition is implemented through a hierarchy of identical microcircuits.[3] The evolutionary benefit to this duplication allowed human neocortex to increase in size by almost 3-fold over just the last 3 million years.[3]

3D reconstruction of five cortical columns in rat vibrissal cortex

The columnar hypothesis states that the cortex is composed of discrete, modular columns of neurons, characterized by a consistent connectivity profile.[5] The columnar organization hypothesis is currently the most widely adopted to explain the cortical processing of information.[10]

Mammalian cerebral cortex
Main article: 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.[11] The number of layers is the same in most mammals, but varies throughout the cortex. In the neocortex 6 layers can be recognized although many regions lack one or more layers, fewer layers are present in the archipallium and the paleopallium.[12]

Columnar functional organization

The columnar functional organization, as originally framed by Vernon Mountcastle,[1] 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.[4][13][14] 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.

Hubel and Wiesel studies

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[15] 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.

Number of cortical columns

There are about 200 million (2×108) cortical minicolumns in the human neocortex with up to about 110 neurons each,[16] 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.[17] Jeff Hawkings claims that there are only 150,000 columns in the human neocortex, based on research made by his company Numenta.[18]

There are claims that minicolumns may have as many as 400 principal cells,[19] but it is not clear if that includes glia cells.

Some contradicts the previous estimates,[20] claiming the original research is too arbitrary.[21] The authors propose a uniform neocortex, and chose a fixed width and length to calculate the cell numbers. Later research pointed out that the neocortex is indeed not uniform for other species,[22] 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.[21][23][24] The actual number of neurons within a single column is variable, and depends on the cerebral areas and thus the function of the column.

See also

References
  1. Mountcastle, Vernon (July 1957). "Modality and topographic properties of single neurons of cat's somatic sensory cortex". Journal of Neurophysiology. 20 (4): 408–34. doi:10.1152/jn.1957.20.4.408. PMID 13439410.
  2. Mountcastle, Vernon (1997). "The columnar organization of the neocortex". Brain. 120 (4): 701–722. doi:10.1093/brain/120.4.701. PMID 9153131.
  3. Bennett, Max (2020). "An Attempt at a Unified Theory of the Neocortical Microcircuit in Sensory Cortex". Frontiers in Neural Circuits. 14: 40. doi:10.3389/fncir.2020.00040. PMC 7416357. PMID 32848632.
  4. Buxhoeveden, D. P. (2002-05-01). "The minicolumn hypothesis in neuroscience". Brain. 125 (5): 935–951. doi:10.1093/brain/awf110. ISSN 0006-8950. PMID 11960884.
  5. Lodato, Simona; Arlotta, Paola (2015-11-13). "Generating Neuronal Diversity in the Mammalian Cerebral Cortex". Annual Review of Cell and Developmental Biology. 31 (1): 699–720. doi:10.1146/annurev-cellbio-100814-125353. PMC 4778709. PMID 26359774. Functional columns were first defined in the cortex by Mountcastle (1957), who proposed the columnar hypothesis, which states that the cortex is composed of discrete, modular columns of neurons, characterized by a consistent connectivity profile.
  6. Kolb, Bryan; Whishaw, Ian Q. (2003). Fundamentals of human neuropsychology. New York: Worth. ISBN 978-0-7167-5300-1.
  7. Horton JC, Adams DL (2005). "The cortical column: a structure without a function". Philos. Trans. R. Soc. Lond. B Biol. Sci. 360 (1456): 837–862. doi:10.1098/rstb.2005.1623. PMC 1569491. PMID 15937015.
  8. Hubel, DH; Wiesel, TN (Mar 1963). "Shape and arrangement of columns in cat's striate cortex". J Physiol. 165 (3): 559–68. doi:10.1113/jphysiol.1963.sp007079. PMC 1359325. PMID 13955384.
  9. Bastos, AM; Usrey, WM; Adams, RA; Mangun, GR; Fries, P; Friston, Karl (2012). "Canonical microcircuits for predictive coding". Neuron. 76 (4): 695–711. doi:10.1016/j.neuron.2012.10.038. PMC 3777738. PMID 23177956.
  10. Defelipe, Javier (2012). "The neocortical column". Frontiers in Neuroanatomy. 6: 5. doi:10.3389/fnana.2012.00022. PMC 3278674. PMID 22347848.
  11. Saladin, Kenneth (2011). Human anatomy (3rd ed.). McGraw-Hill. p. 416. ISBN 9780071222075.
  12. R Nieuwenhuys; HJ Donkelaar; C Nicholson; WJAJ Smeets; H Wicht (1998). The central nervous system of vertebrates. Berlin [u.a.]: Springer. ISBN 978-3540560135.
  13. Hubel DH, Wiesel TN, Stryker MP (September 1977). "Orientation columns in macaque monkey visual cortex demonstrated by the 2-deoxyglucose autoradiographic technique". Nature. 269 (5626): 328–30. Bibcode:1977Natur.269..328H. doi:10.1038/269328a0. PMID 409953. S2CID 4246375.
  14. Leise EM (1990). "Modular construction of nervous systems: a basic principle of design for invertebrates and vertebrates" (PDF). Brain Research. Brain Research Reviews. 15 (1): 1–23. doi:10.1016/0165-0173(90)90009-d. PMID 2194614. S2CID 4996690.
  15. "The Nobel Prize in Medicine 1981". Retrieved 2008-04-13.
  16. Krueger, James M.; et al. (2008). "Sleep as a fundamental property of neuronal assemblies". Nature Reviews Neuroscience. 9 (12): 910–919. doi:10.1038/nrn2521. PMC 2586424. PMID 18985047.
  17. Kazushige Tsunoda; Yukako Yamane; Makoto Nishizaki; Manabu Tanifuji (August 2001). "Complex objects are represented in macaque inferotemporal cortex by the combination of feature columns". Nat. Neurosci. 4 (8): 832–838. doi:10.1038/90547. PMID 11477430. S2CID 14714957.
  18. Hawkins, Jeff (2021). A Thousand Brains: A New Theory of Intelligence. Basic Books. ISBN 978-1541675810. Retrieved 23 January 2023.
  19. O. David, in Brain Mapping (2015). "Acquisition Methods, Methods and Modeling". In Arthur W. Toga (ed.). Brain Mapping – An Encyclopedic Reference. ISBN 9780123973160.
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  21. Rakic, Pasko (2008-08-26). "Confusing cortical columns". Proceedings of the National Academy of Sciences. 105 (34): 12099–12100. Bibcode:2008PNAS..10512099R. doi:10.1073/pnas.0807271105. ISSN 0027-8424. PMC 2527871. PMID 18715998.
  22. Lent, Roberto; Kaas, Jon H.; Wong, Peiyan; Collins, Christine E.; Herculano-Houzel, Suzana (2008-08-26). "The basic nonuniformity of the cerebral cortex". Proceedings of the National Academy of Sciences. 105 (34): 12593–12598. doi:10.1073/pnas.0805417105. ISSN 0027-8424. PMC 2527956. PMID 18689685.
  23. Lent, Roberto; Azevedo, Frederico A. C.; Andrade‐Moraes, Carlos H.; Pinto, Ana V. O. (2012). "How many neurons do you have? Some dogmas of quantitative neuroscience under revision". European Journal of Neuroscience. 35 (1): 1–9. doi:10.1111/j.1460-9568.2011.07923.x. ISSN 1460-9568. PMID 22151227. S2CID 20365568.
  24. Molnár, Z. (January 2013). "Chapter 7 - Cortical Columns". Neural Circuit Development and Function in the Brain: 109–129. doi:10.1016/B978-0-12-397267-5.00137-0. ISBN 9780123972675.
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