Cortical column

A cortical column, also called hypercolumn, macrocolumn,[1] functional column[2] or sometimes cortical module,[3] is a group of neurons in the cortex of the brain that can be successively penetrated by a probe inserted perpendicularly to the cortical surface, and which have nearly identical receptive fields. 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".[4] A cortical module is defined as either synonymous with a hypercolumn (Mountcastle) or as a tissue block of multiple overlapping hypercolumns.[5]

The columnar hypothesis states that the cortex is composed of discrete, modular columns of neurons, characterized by a consistent connectivity profile.[2]

It is still unclear what precisely is meant by the term, and it does not correspond to any single structure within the cortex. It has been impossible to find a canonical microcircuit that corresponds to the cortical column, and no genetic mechanism has been deciphered that designates how to construct a column.[4] However, the columnar organization hypothesis is currently the most widely adopted to explain the cortical processing of information.[6]

Mammalian cerebral cortex

The mammalian cerebral cortex, the grey matter encapsulating the white matter, is composed of layers. The human cortex is roughly 2.4 mm thick. The number of layers is the same in all 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.[7]

Columnar functional organization

The columnar functional organization, as originally framed by Vernon Mountcastle,[8] 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.[1][9][10] 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[11] 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 100,000,000 cortical minicolumns in the neo-cortex with up to 110 neurons each,[12] giving 1-2,000,000 cortical columns. There may be more if the columns can overlap, as suggested by Tsunoda et al..[13]

See also

References

  1. 1 2 Buxhoeveden, D. P. (2002-05-01). "The minicolumn hypothesis in neuroscience". Brain. 125 (5): 935–951. ISSN 0006-8950. doi:10.1093/brain/awf110.
  2. 1 2 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. PMC 4778709 Freely accessible. PMID 26359774. doi:10.1146/annurev-cellbio-100814-125353. 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.
  3. ↑ Kolb, Bryan; Whishaw, Ian Q. (2003). Fundamentals of human neuropsychology. New York: Worth. ISBN 0-7167-5300-6.
  4. 1 2 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. PMC 1569491 Freely accessible. PMID 15937015. doi:10.1098/rstb.2005.1623.
  5. ↑ Hubel, DH; Wiesel, TN (Mar 1963). "Shape and arrangement of columns in cat's striate cortex.". J Physiol. 165: 559–68. PMC 1359325 Freely accessible. PMID 13955384. doi:10.1113/jphysiol.1963.sp007079.
  6. ↑ Defelipe, Javier (2012). "The neocortical column". Frontiers in Neuroanatomy. 6. doi:10.3389/fnana.2012.00022.
  7. ↑ R Nieuwenhuys; HJ Donkelaar; C Nicholson; WJAJ Smeets; H Wicht (1998). The central nervous system of vertebrates. Berlin [u.a.]: Springer. ISBN 3540560130.
  8. ↑ Mountcastle VB (July 1957). "Modality and topographic properties of single neurons of cat's somatic sensory cortex". Journal of Neurophysiology. 20 (4): 408–34. PMID 13439410.
  9. ↑ Hubel DH, Wiesel TN, Stryker MP; Wiesel; Stryker (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. PMID 409953. doi:10.1038/269328a0.
  10. ↑ Leise EM (1990). "Modular construction of nervous systems: a basic principle of design for invertebrates and vertebrates". Brain Research. Brain Research Reviews. 15 (1): 1–23. PMID 2194614. doi:10.1016/0165-0173(90)90009-d.
  11. ↑ "The Nobel Prize in Medicine 1981". Retrieved 2008-04-13.
  12. ↑ Krueger, James M.; et al. (2008). "Sleep as a fundamental property of neuronal assemblies". Nature Reviews Neuroscience. 9 (12): 910–919. PMC 2586424 Freely accessible. PMID 18985047. doi:10.1038/nrn2521.
  13. ↑ 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. PMID 11477430. doi:10.1038/90547.
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