Area origins of L5a, L6a and L6b corticothalamic projections to VPM and Po. Epifluorescence microphotographs showing retrogradely stained neuron somatas in a coronal section of the cerebral cortex from a deposit located in VPM (a) and in Po (b). c, High-magnification detail of L5b corticothalamic-labeled cells. d, High-magnification detail of L6 corticothalamic-labeled cells. e, Cortical column details showing the corticothalamic input patterns in S1BF, S1mv, M1, and S2. f, g, Generation of an isometric surface map of mouse somatic motor and sensory areas. This map was created by aligning all the pial contours of Paxinos and Franklin (2012) coronal section diagrams as parallel lines along the dorsal midline of the cerebral hemisphere (black arrowheads and dashed black line on the map). Yellow dots indicate bregma. h, Flat map detail of the areas used in the subsequent figures to represent the corticothalamic labeling. i, j, Location of ipsilateral labeled cortical neurons: Separate maps are used to represent L5b (magenta), L6a (blue), and L6b (green) cells. Dots represent relative-labeled cell densities. Panels f, g represent the labeling in VPM1 and Po3 cases, respectively. A1: primary auditory area; Cg: cingulate cortex; Ect: ectorhinal area; FrA: frontal association; INS: insular (granular + dysgranular) cortex; M1: primary motor area; M2: secondary motor area; Prh: perirhinal area; S1: primary somatosensory area; S2: secondary somatosensory area; V1: primary visual area. Scale bars: 250 µm (a, b), 25 µm (c, d), and 150 µm (e).