Cortical minicolumn

A cortical minicolumn is a vertical column through the cortical layers containing on the order of 80–120 neurons, except in the primate striate cortex (V1), where the number is more than doubled. There are about 2×108 in humans. From calculations, the diameter of a minicolumn is about 28–40 µm.

Many sources support the existence of minicolumns, especially Mountcastle, with strong evidence reviewed by Buxhoeveden and Casanova 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". See also Calvin's Handbook on cortical columns.

Size
The minicolumn measures of the order of 40–50 µm in transverse diameter (Mountcastle 1997, Buxhoeveden 2000, 2001); 35–60 µm (Schlaug, 1995, Buxhoeveden 19996, 2000, 2001); 50 µm with 80 µm spacing (Buldyrev, 2000), or 30 µm with 50 µm (Buxhoeveden, 2000). Larger sizes may not be of human minicolumns, for example Macaque monkey V1 minicolumns are 31µm diameter, with 142 pyramidal cells (Peters, 1994) — 1270 columns per mm2. Similarly, the cat V1 has much bigger minicolumns, ~56 µm (Peters 1991, 1993).

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 cortex 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 do a similar calculation and arrive at 36 µm (p51, last para).

Facts

 * Cells in 50µm minicolumn all have the same receptive field; adjacent minicolumns may have very different fields (Jones, 2000).
 * Downwards projecting axons in minicolumns are ≈10µm in diameter, periodicity and density similar to those within the cortex, but not necessarily coincident (DePhilipe, 1990).
 * Thalamic input (1 axon) reaches 100–300 minicolumns.
 * The number of fibres in the corpus callosum is 2–5×108 (Cook 1984, Houzel 1999) — perhaps related to the number of minicolumns.