A re-evaluation of the cytoarchitecture of the ventral nuclear complex of the cat's thalamus on the basis of corticothalamic connections

Abstract

Summary A short description has been given of the thalamic nuclei which receive afferent connections from the frontal cerebral cortex and the first and second somatic sensory cortical areas in the cat. The findings reported correspond largely to previous observations on the topography of the thalamus. However, studies on corticothalamic connections have proved to be of value in delimiting some thalamic structures more accurately. The areas of termination of corticothalamic fibres in VPM and VPL from face and limb areas, respectively, of the cerebral cortex are separated by a thick myelinated fibre bundle. Furthermore, a thin fibre bundle separates the 2 parts of VPL which receive afferent fibres from hind- and forelimb areas of the sensorimotor cortical areas. Marked differences in cytoarchitecture help to separate VPMpc and VPI from VPM. However, these nuclei appear to receive afferent connections from largely identical cortical areas. The posterior group of nuclei (PO) is distinct from the ventral group by differences in cytoarchitecture and particulars in the corticothalamic connections. In PO are included the caudal end of VPL1, rostral MGmc and ventral part of caudal LP. It is emphasized that a profound knowledge of fibre connections combined with the use of other methods such as the Golgi technique, histochemistry and electron microscopy, is needed in order to obtain a complete and rational comprehension of thalamic topography.