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A cortical minicolumn (also called cortical microcolumn[1]) 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".[2][3] 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.[4] From calculations, the diameter of a minicolumn is about 28–40 μm.[2] Minicolumns grow from progenitor cells within the embryo and contain neurons within multiple layers (2–6) of the cortex.[5]
Many sources support the existence of minicolumns, especially Mountcastle,[2] with strong evidence reviewed by Buxhoeveden and Casanova[6] 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.[7]
Estimates of number of neurons in a minicolumn range from 80–100 neurons.[6][2][8]
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.
Estimates of the number of neurons in cortex or in neocortex are on the order of 2×1010.[9][10] Most[11] (perhaps 90%[citation needed]) of cortical neurons are neocortical neurons.
Johansson and Lansner[4] 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.[12]
The minicolumn measures of the order of 40–50 μm in transverse diameter;[2][6] 35–60 μm;[citation needed] 50 μm with 80 μm spacing,[citation needed] or 30 μm with 50 μm.[citation needed] Larger sizes may not be of human minicolumns, for example macaque monkey V1 minicolumns are 31 μm diameter, with 142 pyramidal cells[citation needed] — 1270 columns per mm2. Similarly, the cat V1 has much bigger minicolumns, ~56 μm.[citation needed]
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[4] 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.[citation needed]
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