Fig. S1. Microphotographs showing location of all VPM (A) and Po (B) BDA injection sites. The number of labeled axons counted as they cross the striato-pallial border is indicated for each experiment. Scale bars: 100 μm. (C, D) Quantification of VPM and Po total axonal length and boutons following ION section. Values: mean ± SEM. (E, F) Total individual axons effectively labeled by the BDA microinjections was estimated by counting the axonal trunks (arrowheads) at their point of crossing of the striato-pallial border. Cytochrome oxidase counterstain. Scale bars E and F: 500 and 100 μm respectively. (G) High-magnification of labeled terminal cortical branches of VPM axons containing bouton-like varicosities. Scale bar: 5 μm.

Fig. S2. C-Fos expression reflects genuine activation of Po and VPM neurons. (A) Cytochrome oxidase staining showing the distribution of the distinct cortical layers across bins: bin 1 corresponds to L1, bin 2 and 3 to L2/3, bin 4 and 5 to L4, bin 6 to L5A, bin 7 to L5B and bin 8, 9 and 10 to L6. Scale bar: 100 μm. (B) Disinhibition of corticothalamic neurons by bicuculline injection in deep layers of S1BF induces ipsilateral expression of c-Fos in Po neurons. Scale bar: 100 μm. (C) L4 and VPM neurons are strongly activated by exploration of the environment in unclipped mice. Blue arrowheads delineate a barrel. Quantification of bin- (empty circles) and layer-specific (bars) fold-changes in c-Fos+ neuron numbers in response to EE with all whiskers (unclipped mouse). Graph bars are color-coded to indicate the percentage of c-Fos+ neurons in each corresponding layer for active whiskers. Scale bars: 100 μm. (D) Dual whisker environmental exploration and noxious stimulation induces c-Fos expression in SpVc neurons. Scale bars: 100 μm.

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