Extended Data Figure 4. VP afferents target the CB-dense center of somatosensory TRN, whereas POM afferents target the SOM-dense medial and lateral edges.

a, Four representative examples showing the POM injection sites and anterograde projections to TRN in live 300 μm slices. Red: SOM-Cre x tdT. Green: ChR2-eYFP. Boundaries of the thalamic nuclei (TRN outlined by dashed lines) were determined from SOM-Cre X tdT fluorescence and by brightfield images (not shown). Injection sites were located in POM nuclei, seen here as the large, bright eYFP spots medial to TRN. The smaller bands of eYFP along the medial and lateral edges of the somatosensory TRN are axons and terminals from the labeled POM cells. In addition to the TRN edges, POM also targeted layer 5a (L5a) and L1 of barrel cortex (but not L4; data not shown). Top left image shows the injection site for Fig. 2c–d. Experiment replicated in 18 mice.

b, Left, schematic showing recording configuration (also used in the experiments of Fig. 2c–f). Right, additional representative examples of synaptic responses of cells across the medial-lateral axis of somatosensory TRN evoked by POM stimulation. TRN cells near the edges of somatosensory TRN received strong input from POM whereas cells located in the center of TRN did not. Experiments replicated in 5 slices, 5 mice.

c, Similar to a, but for VP afferents. VP afferents clearly targeted the central zone of TRN. VP also projected to L4 of barrel cortex but not L5a or L1 (not shown). Top left image shows the injection site for Fig. 2g–h. Experiments replicated in 25 mice.

d, Similar to (b), but for VP. Left, schematic showing recording configuration (also used in the experiments of Fig. 2g–j). Right, cells in the center of somatosensory TRN received stronger input from VP than did cells located near the edges of TRN. Experiment replicated in 6 slices, 4 mice.