Cortical minicolumn

A cortical minicolumn 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".^[1] 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.^[2] From calculations, the diameter of a minicolumn is about 28–40 μm.^{[citation needed]} Minicolumns grow from progenitor cells within the embryo and contain neurons within multiple layers (2–6) of the cortex.^[3]

Many sources support the existence of minicolumns, especially Mountcastle,^[4] with strong evidence reviewed by Buxhoeveden and Casanova^[5] 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".

Cortical minicolumns can also be called cortical microcolumns.^[6] Cells in 50 μm minicolumn all have the same receptive field; adjacent minicolumns may have different fields.^[7]

Although many studies have observed Neurons structured into cortical columns, it is still widely disputed as to whether they serve a purpose or are even the smallest functional unit of the cortex, or whether Neurons are simply packed in such a way purely for efficient space usage and that the columns otherwise have no other role in Brain function.^[8][9]

Number of neurons[]

Estimates of number of neurons in a minicolumn range from 80–100 neurons.^[5][4][10]

Jones^[7] 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.

Number of minicolumns[]

Estimates of the number of neurons in cortex or in neocortex are on the order of 2×10¹⁰.^[11][12] Most^[13] (perhaps 90%^{[citation needed]}) of cortical neurons are neocortical neurons.

Johansson and Lansner^[2] 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^[14] with no derivation.^{[citation needed]}

Size[]

The minicolumn measures of the order of 40–50 μm in transverse diameter;^[4][5] 35–60 μm;^[15][16] 50 μm with 80 μm spacing,^[17] or 30 μm with 50 μm.^[18] Larger sizes may not be of human minicolumns, for example macaque monkey V1 minicolumns are 31 μm diameter, with 142 pyramidal cells^[19] — 1270 columns per mm². Similarly, the cat V1 has much bigger minicolumns, ~56 μm.^[20]

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^[2] 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.^[21]

See also[]

• Cortical column

References[]

External links[]

• "W. H. Calvin's "Cortical Columns, Modules, and Hebbian Cell Assemblies" (MIT Press 1995)". williamcalvin.com. Retrieved 2017-12-31.