Fig. 13.

A schematic summary of the developmental sequence of POm TCA innervation of barrel cortex in mice (left column) and rats (right column). At P0, POm TCAs are present within the cortical layers in both species, but in mice, many more extend superficially, into the CP, than in rats, where they are mostly confined to deep layers. By P2, layer IV has emerged in both species; POm TCAs are present in layer IV in mice, but are mostly confined to infragranular layers in rats. By P4, barrel cytoarchitecture (dotted lines) and barrel-clusters of VPM TCAs (not shown) are both evident. In both species, POm axons penetrate layer IV and are present within barrels and septa; a greater proportion of POm TCAs in rats now extends superficially in comparison with mice. The major features of a mature-like pattern of POm TCA innervation emerge slightly earlier in rats (P5–8) in comparison with mice (P7–9). WM, white matter.