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Uncovering temporal structure in hippocampal output patterns.
Place cell activity of hippocampal pyramidal cells has been described as the cognitive substrate of spatial memory. Replay is observed during hippocampal sharp-wave-ripple-associated population burst events (PBEs) and is critical for consolidation and recall-guided behaviors. PBE activity has historically been analyzed as a phenomenon subordinate to the place code. Here, we use hidden Markov models to study PBEs observed in rats during exploration of both linear mazes and open fields. We demonstrate that estimated models are consistent with a spatial map of the environment, and can even decode animals' positions during behavior. Moreover, we demonstrate the model can be used to identify hippocampal replay without recourse to the place code, using only PBE model congruence. These results suggest that downstream regions may rely on PBEs to provide a substrate for memory. Additionally, by forming models independent of animal behavior, we lay the groundwork for studies of non-spatial memory
A framework to identify structured behavioral patterns within rodent spatial trajectories
Animal behavior is highly structured. Yet, structured behavioral patterns—or “statistical ethograms”—are not immediately apparent from the full spatiotemporal data that behavioral scientists usually collect. Here, we introduce a framework to quantitatively characterize rodent behavior during spatial (e.g., maze) navigation, in terms of movement building blocks or motor primitives. The hypothesis that we pursue is that rodent behavior is characterized by a small number of motor primitives, which are combined over time to produce open-ended movements. We assume motor primitives to be organized in terms of two sparsity principles: each movement is controlled using a limited subset of motor primitives (sparse superposition) and each primitive is active only for time-limited, time-contiguous portions of movements (sparse activity). We formalize this hypothesis using a sparse dictionary learning method, which we use to extract motor primitives from rodent position and velocity data collected during spatial navigation, and successively to reconstruct past trajectories and predict novel ones. Three main results validate our approach. First, rodent behavioral trajectories are robustly reconstructed from incomplete data, performing better than approaches based on standard dimensionality reduction methods, such as principal component analysis, or single sparsity. Second, the motor primitives extracted during one experimental session generalize and afford the accurate reconstruction of rodent behavior across successive experimental sessions in the same or in modified mazes. Third, in our approach the number of motor primitives associated with each maze correlates with independent measures of maze complexity, hence showing that our formalism is sensitive to essential aspects of task structure. The framework introduced here can be used by behavioral scientists and neuroscientists as an aid for behavioral and neural data analysis. Indeed, the extracted motor primitives enable the quantitative characterization of the complexity and similarity between different mazes and behavioral patterns across multiple trials (i.e., habit formation). We provide example uses of this computational framework, showing how it can be used to identify behavioural effects of maze complexity, analyze stereotyped behavior, classify behavioral choices and predict place and grid cell displacement in novel environments
Neural population activity, multi-variate statistics (Byron Yu)
Presented on November 6, 2019 at 10:30 a.m. in the Parker H. Petit Institute for Bioengineering and Biosciences Building, Room 1128.Aaron Batista is an assistant professor of bioengineering at the University of Pittsburgh. His research interests include brain-machine interfaces and neurophysiology of sensory-motor coordination.Ranu Jung is a Professor and Chair of Biomedical Engineering at Florida International University. Her research interests include neural Engineering, computational neuroscience, sensorimotor integration.Caleb Kemere is an Associate Professor of Electrical and Computer Engineering and an Assistant Professor in Bioengineering at Rice University. His research consists of building interfaces with memory and cognitive processes, model-based signal processing, and low-power embedded systems.Karen Rommelfanger is the Program Director of Emory University's Neuroethics Program at the Center for Ethics and is an Assistant Professor in the Department of Neurology and in the Department of Psychiatry at Emory University.Byron Yu is the Gerard G. Elia Career Development Professor of Electrical & Computer Engineering and Biomedical Engineering at Carnegie Mellon University.Runtime: 115:01 minute