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Cortical column

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Cortical columns are groups of cells in the cerebral cortex that are arranged in columns. The term cortical column was originally defined in a functional context but since no functions of columnar arrangements in the cortex could be unambiguously identified either within or across species (for review, see Horton & Adams, 2005), the more narrow term ontogenetic column has come to be preferred (Rakic 1988). An ontogenetic column consists of ontogenetic clones of the same precursor neuron. They are arranged radially according to the number of cell cycles of the precursor: while the older postmitotic neurons remain in the deep layers, the younger ones migrate to the superficial layers of the cortex, following the marginal zone.

Significance

Since the middle of the founding work by Vernon Mountcastle and colleagues (e.g. Mountcastle 1957 who introduced the term column in this cortical context), cortical columns have been widely regarded as the basic computational unit of the neocortex (cf. Mountcastle 1978), with their quantity being the main determinant of the intelligence of a specific mammal and the general intelligence of its species. Following an influential paper by Rockel et al. (1980), cortical columns are generally assumed to be uniformly organized across brain areas within a species (with the exception of the primate visual cortex) and across mammalian species. They are usually described in terms of macrocolumns which consist of an uncertain number of minicolumns (that may correspond to ontogenetic columns) that are found throughout the neocortex, with a diameter of roughly 0.5mm which is also about the distance between the center of two separate columns.

Controversy

The view of the uniformity of the mammalian neocortex has been challenged repeatedly (cf. Haug 1987, Herculano-Houzel et al., 2008 and Rakic 2008), which gave rise to the notion of ontogenetic columns.

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