Thalamic posterior ventral neurons with bifurcating axons to the first and second somatosensory areas in the cat, demonstrated by the fluorescent retrograde double labeling technique.

The thalamic posterior ventral neurons with bifurcating axons to both the first and second somatosensory cortical areas (SI and SII) in the cat were examined by the fluorescent retrograde double labeling technique. After injection of Evans blue (EB) into the SI, and of 4',6-diamidino-2-phenylindol.2HCl (DAPI) into the SII of the same hemisphere, EB- and DAPI-labeled cells were observed predominantly in both the posterolateral ventral and the posteromedial ventral nuclei of the thalamus. Although EB single-labeled and DAPI single-labeled cells tended to occupy separate regions within the posterior ventral nuclei, a small number of cells double-labeled with both EB and DAPI were detected in the border zone between two single-labeled cell groups. These observations indicate that some cells in the posteromedial and posterolateral ventral nuclei project both to the SI and SII by bifurcating axons.