Cortical minicolumn

A cortical minicolumn is a vertical column through the cortical layers of the brain, comprising 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.^[1] From calculations, the diameter of a minicolumn is about 28–40 µm^{[citation needed]}.

Many sources support the existence of minicolumns, especially Mountcastle,^[2] with strong evidence reviewed by Buxhoeveden and Casanova^[3] 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 1996, 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 31 µm 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^[4] do a similar calculation and arrive at 36 µm (p51, last para).

Facts

• Cells in 50 µm minicolumn all have the same receptive field; adjacent minicolumns may have very different fields (Jones, 2000).
• Downwards projecting axons in minicolumns are ≈10 µm 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.

References

1. ^ Towards cortex sized artificial neural systems, Christopher Johansson and Anders Lansner, Neural Networks, Vol. 20 #1, pp48–61, Elsevier, January 2007
2. ^ The columnar organization of the neocortex, Vernon B. Mountcastle, Brain, Vol. 20 #4, pp701–722, Oxford University Press, April 1997
3. ^ The minicolumn hypothesis in neuroscience, Daniel P. Buxhoeveden and Manuel F. Casanova, Brain, Vol. 125 #5, pp935–951, Oxford University Press, May 2002.
4. ^ Towards cortex sized artificial neural systems, Christopher Johansson and Anders Lansner, Neural Networks, Vol. 20 #1, pp48–61, Elsevier, January 2007

See also

• Cortical column