A cortical minicolumn (also called cortical microcolumn<ref>Template:Cite journal</ref>) is a vertical column through the cortical layers of the brain. Neurons within the microcolumn "receive common inputs, have common outputs, are interconnected, and may well constitute a fundamental computational unit of the cerebral cortex".<ref name="Mountcastle1957">Template:Cite journal</ref><ref>Template:Cite journal</ref> Minicolumns comprise perhaps 80–120 neurons, except in the primate primary visual cortex (V1), where there are typically more than twice the number. There are about 2×108 minicolumns in humans.<ref name=":0">Template:Cite journal</ref> From calculations, the diameter of a minicolumn is about 28–40 μm.<ref name="Mountcastle1957" /> Minicolumns grow from progenitor cells within the embryo and contain neurons within multiple layers (2–6) of the cortex.<ref>Jeff Hawkins, Sandra Blakeslee On Intelligence p. 94</ref>

File:Bennet2020Figure2CorticalColumn.jpg
Visualization of cortical minicolumns within a macrocolumn

Many sources support the existence of minicolumns, especially Mountcastle,<ref name="Mountcastle1957" /> with strong evidence reviewed by Buxhoeveden and Casanova<ref name=":2">Template:Cite journal</ref> who conclude "... the minicolumn must be considered a strong model for cortical organization" and "[the minicolumn is] the most basic and consistent template by which the neocortex organizes its neurones, pathways, and intrinsic circuits".

Cells in 50 μm minicolumn all have the same receptive field; adjacent minicolumns may have different fields.<ref name="Jones2000"/>

Number of neuronsEdit

Estimates of number of neurons in a minicolumn range from 80–100 neurons.<ref name=":2" /><ref name="Mountcastle1957" /><ref>Sporns O, Tononi G, Kötter R. The human connectome: A structural description of the human brain. PLoS Comput. Biol. 2005 Sep1(4):e42.</ref>

Jones<ref name="Jones2000">Template:Cite journal</ref> describes a variety of observations that may be interpreted as mini- or micro-columns and gives example numbers from 11 to 142 neurons per minicolumn.

File:Cortical Minicolumn.png
3D render of a cortical minicolumn in the mouse visual cortex

Number of minicolumnsEdit

Estimates of the number of neurons in cortex or in neocortex are on the order of 2×1010.<ref name="Neocortical Neuron Number in Humans: Effect of Sex and Age">Template:Cite journal</ref><ref name="Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain">Template:Cite journal</ref> Most<ref name="Lippincott’s Illustrated Reviews: Neuroscience">Claudia Krebs MD PhD, Joanne Weinberg PhD, Elizabeth Akesson MSc. Lippincott’s Illustrated Reviews: Neuroscience, accessed Nov 10 2013. Chapter 13, II.A, "Histological organization of the cortex"</ref> (perhaps 90%Template:Citation needed) of cortical neurons are neocortical neurons.

Johansson and Lansner<ref name=":0" /> use an estimate of 2×1010 neurons in the neocortex and an estimate of 100 neurons per minicolumn, yielding an estimate of 2×108 minicolumns.

Sporns et al. give an estimate of 2×107 – 2×108 minicolumns.<ref name="The human connectome: A structural description of the human brain">Sporns O, Tononi G, Kötter R. The human connectome: A structural description of the human brain. PLoS Comput. Biol. 2005 Sep1(4):e42</ref>

Size of minicolumnsEdit

The minicolumn measures of the order of 40–50 μm in transverse diameter;<ref name="Mountcastle1957" /><ref name=":2" /> 35–60 μm;Template:CN 50 μm with 80 μm spacing,Template:CN or 30 μm with 50 μm.Template:CN Larger sizes may not be of human minicolumns, for example macaque monkey V1 minicolumns are 31 μm diameter, with 142 pyramidal cellsTemplate:CN — 1270 columns per mm2. Similarly, the cat V1 has much bigger minicolumns, ~56 μm.Template:CN

The size can also be calculated from area considerations. If cortex (both hemispheres) is 1.27×1011 μm2 then if there are 2×108 minicolumns in the neocortex then each is 635 μm2, giving a diameter of 28 μm (if the cortex area were doubled to the commonly quoted value, this would rise to 40 μm). Johansson and Lansner<ref name=":0" /> do a similar calculation and arrive at 36 μm (p51, last para).

Downwards projecting axons in minicolumns are ≈10 μm in diameter, periodicity and density similar to those within the cortex, but not necessarily coincident.Template:CN

See alsoEdit

ReferencesEdit

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External linksEdit

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