316 — Lattice system of functionally distinct cell types in the neocortex

Subcerebral projection neurons (SCPNs) are an excitatory cell type found in layer 5 of neocortex in mouse brain. The direct neighborhood of the brain in the vicinity of SCPNs appears to tile across cortex in ‘microcolumns.’ The authors sought to better understand the distribution and arrangement of these microcolumns.

Using AAV traces in two-photon in-vivo microscopy, the researchers found that layer 5 in both primary sensory as well as motor cortices organize into these cell-type-specific microcolumns, where each SCPN-surrounding microcolumn seems to contain standalone circuitry.

Previous research suggests that genetically similar cells tend to have similar orientation- (or other stimulus) selectivity. These columns are not closely clonally related, and so it’s instead more likely that there is some stimulus that these microcolumns synergistically respond to.

Rodents don’t appear to have ocular-dominance or orientation-selective columns; but these mice clearly have microcolumns (~40μm, instead of the ~500μm diameter of an ODC). Perhaps orientation-selective “macro”columns — roughly the same size as microcolumns in this research — have the same underlying developmental mechanism as microcolumns, or perhaps there is some lattice-structure semi-fractal growth pattern that is common to all cortical columns.