Afferent Cortical Connectivity to Rodent Posterior Parietal Cortex Along the Mediolateral Axis

Abstract

The posterior parietal cortex (PPC), which can be found in rodents and primates, is thought to be a multimodal convergence area that is interconnected with important visual, auditory, somatosensory, motor and vestibular regions. The PPC is responsible for complex processes such as forming intentions, directing attention, spatial processing and sensorimotor integration. These processes all contribute to decisionmaking. Though rodents would serve as a good model organism for studying the PPC, the anatomy and connectivity of this area are poorly characterized in rats, especially regarding corticocortical projections to the PPC. This thesis analyzes differences in cortical projections to the PPC using fluorescent retrograde Cholera Toxin B subunit (CTB) neuronal tracers to find patterns of connectivity and to define the border between dysgranular retrosplenial cortex (RSD) and medial PPC (mPPC) as well as between mPPC and lateral PPC (lPPC). The borders we identify are consistent with the Paxinos and Watson atlas delineations that were made previously on the basis of cytoarchitecture. We provide connectivity-based evidence to support the existence of at least two subregions. Finally, we examine frontal orienting field (FOF) projections to the PPC in order to test the reciprocity of connectivity between these two regions. Our results are compared to the afferent connectivity of primate PPC. Finally, we suggest a series of future experiments that may elucidate the functional connectivity of the PPC using the results of this anatomical study. Characterizing the subdivisions and connectivity of the rodent PPC will hopefully permit more accurately targeted future experiments that may give insight into the characteristics of this important component of decision-making.