Biology subjects

Burwell, R. D.

Publications and source records attributed to Burwell, R. D..

3 recordsLinked to original sources

bioRxiv2022

NEURONS IN THE POSTRHINAL CORTEX ENCODE NONSPATIAL CONTEXT DURING VISUAL BICONDITIONAL DISCRIMINATION

Spatial context, or the physical surroundings that form the background of an experience, is an essential component of episodic memory. The rodent postrhinal cortex and its primate homolog, the parahippocampal cortex, are thought to preferentially process visuospatial information to represent the spatial features of contexts and scenes. In this study, we addressed open questions about postrhinal function and about how context modulates behavior and cognition. The first question was whether the postrhinal cortex also represents nonspatial contexts. The second question was how representations of context might interact with other cues in the environment. We recorded postrhinal neurons as rats performed a visual nonspatial biconditional discrimination task in which the pattern on the floor determined which object in a pair was correct. Critically, this task design allowed dissociation of location from non-spatial context. We found that postrhinal ensembles and neurons signaled changes in non-spatial context and coded for conjunctions of non-spatial context and objects. Importantly, postrhinal neurons coded for conjunctions of context and objects more often than they coded for conjunctions of location and object. The pattern of findings suggests that postrhinal representations of context may behave like occasion setters by modulating the meaning of other cues in the environment.

neuroscience↗

bioRxiv2021

Social preference in rats not impacted by posterior parietal activity despite overall changes in familiarity-based social behavior

Recent literature points to a potential link between the evolution of complex social behavior and the posterior parietal cortex (PPC) in primates including humans (Parkinson & Wheatley, 2013). Thus far, this theory has been overlooked in other highly social animals that may have also evolved due to social selective pressures. In rodents, there is limited knowledge on the involvement of the PPC on sociality, and most studies of such behavior are limited to understanding social preference. We investigated the role of the PPC through two experiments using the 3-Chamber Sociability and Social Novelty test in rats (Crawley, 2004). In Experiment 1, we used a standard 3-Chamber paradigm, which included two novel demonstrators. In Experiment 2, this paradigm was altered to increase the difference in familiarity between demonstrators such that one demonstrator was highly familiar to the subject and the other was entirely novel. Rats with pre-testing permanent neurotoxic lesions were compared to sham surgery control rats, and the same rats were used for both experiments. Experiments 1 and 2 showed that both groups of rats preferred general social interaction, suggesting no deficit in sociability following PPC damage, regardless of demonstrator identity. Further, experimental and control rats showed similar levels of novelty preference following PPC damage, with novelty preferences increasing in Experiment 2. We argue that heightened novelty preference in Experiment 2 may reflect the increased difference in familiarity between demonstrators. Within the confines of the 3-Chamber task, our results suggest that PPC function was not required for general sociability or social novelty recognition. Because the PPC is implicated in abstract cognition, we argue that existing social tests in rodents may not adequately measure the complex cognitive capacities thought to be supported by the PPC. Future studies should investigate the role of the PPC in social cognition by employing behavioral tasks that require higher cognitive demand rather than testing inherent preference for social partners. Outside of our investigation of the PPC, these results show that social novelty preference can be manipulated through changes in familiarity of demonstrators, and that rats can discriminate others social identities.

animal behavior and cognition↗

bioRxiv2020

Instantaneous amplitude and shape of postrhinal theta oscillations differentially encode running speed

Hippocampal theta oscillations have a temporally asymmetric waveform shape, but it is not known if this theta asymmetry extends to all other cortical regions involved in spatial navigation and memory. Here, using both established and improved cycle-by-cycle analysis methods, we show that theta waveforms in the postrhinal cortex are also temporally asymmetric. On average, the falling phase of postrhinal theta cycles lasts longer than the subsequent rising phase. There are, however, rapid changes in both the instantaneous amplitude and instantaneous temporal asymmetry of postrhinal theta cycles. These rapid changes in amplitude and asymmetry are very poorly correlated, indicative of a mechanistic disconnect between these theta cycle features. We show that the instantaneous amplitude and asymmetry of postrhinal theta cycles differentially encode running speed. Although theta amplitude continues to increase at the fastest running speeds, temporal asymmetry of the theta waveform shape plateaus after medium speeds. Our results suggest that the amplitude and waveform shape of individual postrhinal theta cycles may be governed by partially independent mechanisms and emphasize the importance of employing a single cycle approach to understanding the genesis and behavioral correlates of cortical theta rhythms.

neuroscience↗