Figure 4.

Spatial patterns of axonal arbors in the thalamus from deep-layer CT neurons of the primary somatosensory (S1) cortex. A, Left, Schematic demonstrating connectivity of L6 CT neurons of a single-barrel column of S1 cortex. Upper L6 neurons (gray) project to the VB, forming thin discoid axonal arbors in the intermediate/outer tier of the TRN. Lower L6 neurons (light blue) project to the VB and POm, sending collaterals to form axonal arbors mainly in the inner tier of the TRN. The dark blue terminals in the VB indicate coextensive terminals of upper and lower L6 neurons (modified from Bourassa et al., 1995). Right, Diagram of the proposed organization of the somatosensory sector of the TRN. Filled circles and boxes indicate somata and axon terminals, respectively. Lines indicate axons or dendrites. Dotted boxes and lines indicate occasionally observed projections. i, Inner tier; m, middle tier; o, outer tier. Axonal projection patterns of VB neurons to the TRN (question marks) are not clearly reported. This diagram is mainly based on previous anatomical studies (Crabtree, 1992; Bourassa et al., 1995; Pinault et al., 1995). B–D, Fluorescent images of three serial TC slices containing EYFP-expressing CT fibers originating from a single small injection of virus into the deep S1 cortex. White dotted line in C indicates the TRN border. E, Low-magnification fluorescent image of the slice containing the area shown in C. F, Bright-field image of the TRN area of C. G, High-magnification image of the TRN area marked by the white arrow in C. VPm, Ventral posterior medial nucleus; VPl, ventral posterior lateral nucleus.