Somata of layer V projection neurons in the mouse barrelfield cortex are in preferential register with the sides and septa of the barrels

The spatial distribution of retrogradely labeled neurons of layer V in the posteromedial barrel subfield of the SI mouse cortex efferent to multiple cortical and subcortical structures is mapped with respect to the overlying patterns of layer IV barrels following injections of horseradish peroxidase into the selected target structures. In serial sections tangential to the pial surface, labeled neurons are mapped relative to the outer, middle and inner areal thirds of each of the overlying barrels 2-4 and intervening septa of rows C and D. Labeled neurons, each of which projects to one of the particular target areas, are in register preferentially with the periphery of the barrels and not positioned uniformly below the barrels.