TC slice configuration and the origin of TC inputs to layer 4. A, TC slice configuration. bc, Barrel cortex; th, thalamus; h, hippocampus; str, striatum. Asterisks indicate typical sites for recording (red) and stimulation (blue). Scale bar, 1 mm. B, Top, Mean EPSC responses to laser-scanning photostimulation of 16 sites within a grid placed over the thalamic region of an example slice. Each trace depicts the average response at one stimulation site. The green rectangle demarcates the clearest synaptic inputs. Bottom, Color-coded input map for the full grid (18 × 18 sites); same example slice as in the top panel. The small green rectangle represents the region of origin of the clearest inputs (same as the green rectangle in the top panel). C, Thalamic stimulation region and region of origin of clearest inputs relative to VPM and PoM, same example slice as B. Large green square depicts full photostimulation grid from B, bottom, 1350 μm on the side; the small rectangle is the region of origin of clearest inputs, as in B. Scale bar, 500 μm. D, The thalamic stimulation region (large square) and the region of origin of clearest inputs (small polygon) for a layer 4 recording in a different slice. Thalamic inputs to layer 4 neurons originate in VPM. Scale bar, 500 μm.