Analysis of Afferent Connectivity to the Rat Lateral and Medial Posterior Parietal Cortex

Abstract

In order to investigate the neuronal networks that guide mammalian orienting and navigating behavior, we have characterized the connectivity of the Posterior Parietal Cortex (PPC). The PPC integrates information from many sensory modalities to develop internal representations of the world (spatial maps), direct attention to novel stimuli, and guide movements. To execute these functions, the PPC receives input from many regions, including subcortical regions such as the thalamus and basal ganglia. However, the PPC’s connectivity to these regions has not yet been completely characterized. Homology with primates and regional architectural differences between medial and lateral PPC suggests the existence of subregions within the PPC. However, these regions have yet to be characterized. By injecting an array of retrograde tracers into different locations laterally spaced across the rat PPC at 3.8 mm posterior to Bregma, we have investigated differential afferent connectivity from the subcortex between the medial and lateral PPC. Here we have shown that based on thalamic nuclei projections, PPC connectivity changes from lateral to medial PPC. Medial PPC (mPPC) connects primarily to the medial portions of the Lateral Posterior (LP) nuclei while lateral PPC (lPPC) connects to their lateral subnuclei. By characterizing PPC connectivity, we have shed light on the principles underlying rat cortical networks. Hopefully these findings move us closer to the ultimate goal of understanding a higher-functioning circuits in the human brain.