Research

The Burwell Laboratory studies the structure and function of the cortical regions that surround the hippocampus. For over half a century, the hippocampus has been the focus of research on the neural basis of memory. In primates this system is referred to as the medial temporal lobe (MTL). In rats, we prefer to use the term hippocampal system (HS) because the cortex of the rat brain is smooth and is not divided into discrete lobes. The HS consists of several interconnected structures, including the hippocampal formation(the dentate gyrus, fields CA3, CA2, and CA1, and the subiculum) and the parahippocampal region (perirhinal (PER), postrhinal(POR)/parahippocampal, and entorhinal cortices, the pre- and parasubiculum). These regions exhibit substantial cellular, structural, and connectional homology across rodent and primate brains. Because of this homology, we think that rodents provide an excellent animal model of human MTL function and the neural bases of memory.

Current Areas of Interest

The postrhinal cortex and attention: Research conducted in the Burwell lab suggests that the connectivity between the posterior parietal and postrhinal cortices provides a gateway for attention into the medial temporal lobe memory system. 

How environmental context is represented in the brain: Our studies suggest that the postrhinal cortex combines spatial information from the posterior parietal and retrosplenial cortices with object information from perirhinal cortex to form representations of context.

Understanding representations of objects and landmarks: Our studies suggest that there are two classes of items processed in the hippocampus, some are used for orientation (landmarks) and others are used for other purposes, for example defining context or associative learning.

Disorders of the Cerebrospinal Fluid (CSF): CSF disorders, such as normal pressure hydrocephalus (NPH), impact memory and other cognitive processes. Evidence suggests that the hippocampus and parahippocampal region are impacted in this disorder. In collaboration with Dr. Petra Klinge, we have developed the kaolin model of NPH. Our goal is to use the model to understand and treat associated cognitive deficits.

Methods

Our primary technique to address questions of interest is electrophysiology in behaving animals. We have three Plexon data collection systems, each interfaced with a Plexon CinePlex tracking system and a Med Associates behavioral control system. Each system is interfaced with our Biconditional Discrimination Task in which the pattern on the floor determines which object is correct. 

Although we do use experimental lesion approaches, we are also now also combining multisite recording with optogenetic approaches to both activate and suppress neuronal activity in behaving animals. 

We use behavior, electrophysiology, and optogenetics to understand how hippocampal and parahippocampal structures interact to support memory and other cognitive processes. These very powerful tools allow us to modulate both neuronal activity and behavior.

Funding

NIMH 1R01MH108729-01: Circuit analysis of corticohippocampal interactions in memory (12/15/2015-12/14/2020). PI: Burwell
The goal of this grant is to understand how MTL structures interact to represent and use object and context information in the service of cognition and behavior. Multisite electrophysiology and optogenetic manipulation in behaving rodents will be used to examine how the PER, POR and HC interact to represent contexts and objects, laying the ground work for understanding how context is represented in the brain and how such representations are used to guide cognition and behavior.

NSF IOS-1656488: Circuit analysis of recognition memory (05/01/2017-4/30/2021). PI: Burwell
We recently published evidence for a new function for temporal coding such that the specific frequency of synchronous neuronal activity in the perirhinal cortex transmits specific information about the novelty and familiarity of individual items. The implication is that these signals are used to guide appropriate exploratory behaviors. The goal of this grant is to elucidate the circuits and mechanisms underlying temporal coding in the perirhinal cortex.

P20GM103430: RI-INBRE Program Collaborative Proposal - Functional differentiation of the posterior parietal cortex (05/01/2017-4/30/2019). Co-PIs: R.D. Burwell and V.L. Templer (Providence College).
Recent evidence suggests the primate dorsal posterior parietal cortex (PPC) is involved in top-down attention whereas, the ventral/caudal PPC is involved in bottom-up attention. The primate and rat PPC are likely largely conserved across species and recent work suggests this extends to functional differentiation. The goal of this grant is to further understand functional differentiation in the PPC using a rodent model of the primate brain.