Investigator: Victoria Templer, Providence College
Theme: Neuroscience
Title: Top-down and bottom-up processing in the posterior parietal cortex
Award: SURF PUI Training Award (2022-2024)

Abstract: The purpose of this project is to determine the functional contribution of the rat posterior parietal cortex (PPC) to specific forms of information processing. The PPC has been generally shown to be involved in spatial processing, but debate exists about the role of the rat PPC in visuospatial attention and memory. Specifically, the degree to which the rat PPC contributes to top-down vs. bottom-up attention has yet to be explored. Recent evidence suggests the primate dorsal PPC (dPPC) is involved in top-down attention and may be guiding behavior based on intention while the ventral/caudal (cPPC) is involved in bottom-up attention (Shomstein, 2012) that may reflect less highly processed stimulus salience. Given that the primate and rat PPC is largely conserved across species, the gap in knowledge about the possibility of a functional differentiation existing in the rat PPC is exacerbated by the lack of consensus on the neuroanatomical definition of the rat PPC. To our knowledge, rat electrophysiological and experimental lesion studies have targeted only the dorsal portion of the PPC, ignoring the caudal limb (Swanson, 1992). In Specific Aim 1, we will use chemogenetics to inactivate the dPPC and cPPC and test animals on three different simple object tasks that rely primarily on bottom-up attention. Again, using chemogenetics, in Specific Aim 2 subjects will complete parallel object tasks in a complex, rather than simple environment (Specific Aim 1), designed to tap top-down memories of the spatial arena. Together, this will allow us to dissociate the contribution of PPC sub-regions to top-down and bottom-up attention. Given our preliminary lesion and electrophysiology data, and our survey of the literature, the hypothesis is that the rat dPPC is biased toward top-down attention and the cPPC is biased toward stimulus-guided responses. We are well- positioned to do this because we have lesioned the entire PPC and dPPC in a large cohort of animals, allowing localization of the inclusive structure and its functional contribution to tasks that require both top- down and bottom-up processing. We have also validated our chemogenetic methods and behavioral methods. Behavioral and anatomical results from our previous permanent lesions as well from our temporary inactivations will result in several publications as well as robust preliminary data for an R15 grant. Establishing this highly-accessible rodent model is necessary to unite the primate and rodent literature so that future treatments in diseases of memory can be refined. This project provides excellent training for undergraduates who are interested in advanced degrees in neuroscience.

Relevance: Findings will have translational health relevance due to the posterior parietal cortex (PPC)’s significant role in attention and memory and corresponding dysfunction as a result of several forms of dementia and deterioration from old age. Progress in disease prevention and treatment of dementias depends on localization of the specific brain structures and cognitive processes responsible for distorted information and memory processing.