Posterior parietal cortex of the rat: Architectural delineation and thalamic differentiation.

This study refines the characterization of the rat parietal cortical domain in terms of cyto- and chemoarchitecture as well as thalamic connectivity. We recognize three subdivisions of the posterior parietal cortex (PPC), which are architectonically distinct from the neighboring somatosensory and visual cortices. Furthermore, we show that the different parietal areas are differently connected with thalamic nuclei. The medial portion of PPC (mPPC) is connected primarily with the medial portion of the lateral posterior nucleus (LP), whereas the lateral portion (lPPC) connects with the posterior complex (Po). The more caudolateral part of PPC (PtP) also projects to Po but can be distinguished from lPPC based on architectonic criteria. The primary somatic and visual cortices, neighboring PPC, are preferentially connected with the primary ventral posterior and dorsolateral geniculate nuclei, respectively, and less with the associational Po and LP. Particularly the border between the secondary visual cortex and the PPC has been a matter of controversy, but here we show that, although PPC subareas are connected with Po and medial LP, the medial and lateral secondary visual cortices are connected with lateral LP and a portion of medial LP different from that connected with PPC. The resulting delineations and specifications of connectivity with thalamic nuclei together with upcoming studies of cortical connectivity will facilitate detailed studies on the role of the subdivisions of PPC in the rat as diverse, higher order associative cortical areas, comparable to those described in the primate.for J. Comp. Neurol. 524:3774-3809, 2016.