Browsing by Author "Dutta, Shayok"
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Item Analysis and Application of a Realtime Closed-loop Hippocampal Sharp-wave Ripple Disruption System(2019-08-09) Dutta, Shayok; Kemere, Caleb TClosed-loop modulation of neural activity facilitates causal tests of hypothesis to link temporal neural circuit functions to behavior and cognition. One such dynamically-changing neural circuit in the brain is the hippocampus, responsible for learning and memory. Transient bursts of neural activity in the hippocampus during periods of quiescence, sharp-wave ripple (SWR) events --- ≈80--150 ms periods comprising large 150--250 Hz oscillations --- have previously been established to serve a critical role in memory consolidation and recall through selective closed-loop interactions. The timescale within which these events occur indicate that latency in systems used for closed-loop perturbations is of significant consequence when compared to other longer-lasting events. However, though this approach is beginning to become widespread, performance trade-offs involved in the fabrication of SWR detection and disruptions have not been fully characterized, thereby, limiting the understanding of results using this experimental procedure. In this thesis, I present the development and characterization of a low-latency closed-loop system for SWR detection and modulation engineered to interface with two separate widely-used neural data acquisition hardware platforms. The analysis and characterization of the system is done with a two-pronged approach: (1) generation of a synthetic data to model SWR activity in order explore the parameter space of the realtime detection algorithm and (2) quantification of the realtime in vivo performance of the algorithm and system via offline simulation. Lastly, realtime in vivo detections of SWRs are shown match the simulated detections with added hardware data transmission latency. By performing this characterization, I have established a framework for analyzing other closed-loop systems for neural perturbations. Next, I deploy this system in a neuroscientific closed-loop experiment. In particular, rodents have an innate curiosity to explore novel contexts and objects resulting in the spending more time with novel objects than familiar ones. Work has been done through targeted lesion studies to establish hippocampal dependence of this object recognition memory via novel object test (NOT) paradigms. More recent work has explored correlations of hippocampal CA1 signatures, such as fast-gamma oscillations, to be of importance in NOT object-place recognition memories and demonstrated predictable changes in SWRs. More specifically, SWRs have been shown to increase after encoding of novel objects (or familiar objects in novel locations) and general novelty in the test; however, the concomitant spiking activity has not been correlated with object-place pairings leading to questioning the role of these events in object-place recognition memories. By using the previously engineered system, I demonstrate preliminary results showing suppression of this novelty preference in a rat during a hippocampally dependent novel object test paradigm. This preliminary finding suggests SWRs play a role in object-place recognition memory and not just in sequential goal oriented experimental paradigms as previous results have shown.Item Analysis of an open source, closed-loop, realtime system for hippocampal sharp-wave ripple disruption(IOP Publishing, 2018) Dutta, Shayok; Ackermann, Etienne; Kemere, CalebObjective. The ability to modulate neural activity in a closed-loop fashion enables causal tests of hypotheses which link dynamically-changing neural circuits to specific behavioral functions. One such dynamically-changing neural circuit is the hippocampus, in which momentary sharp-wave ripple (SWR) events—≈ 100 ms periods of large 150–250 Hz oscillations—have been linked to specific mnemonic functions via selective closed-loop perturbation. The limited duration of SWR means that the latency in systems used for closed-loop interaction is of significant consequence compared to other longer-lasting circuit states. While closed-loop SWR perturbation is becoming more wide-spread, the performance trade-offs involved in building a SWR disruption system have not been explored, limiting the design and interpretation of paradigms involving ripple disruption. Approach. We developed and evaluated a low-latency closed-loop SWR detection system implemented as a module to an open-source neural data acquisition software suite capable of interfacing with two separate data acquisition hardware platforms. We first use synthetic data to explore the parameter space of our detection algorithm, then proceed to quantify the realtime in vivo performance and limitations of our system. Main results. We evaluate the realtime system performance of two data acquisition platforms, one using USB and one using ethernet for communication. We report that signal detection latency decomposes into a data acquisition component of 7.5–13.8 ms and 1.35–2.6 ms for USB and ethernet hardware respectively, and an algorithmic component which varies depending on the threshold parameter. Using ethernet acquisition hardware, we report that an algorithmic latency in the range of ≈20–66 ms can be achieved while maintaining <10 false detections per minute, and that these values are highly dependent upon algorithmic parameter space trade-offs. Significance. By characterizing this system in detail, we establish a framework for analyzing other closed-loop neural interfacing systems. Thus, we anticipate this modular, open-source, realtime system will facilitate a wide range of carefully-designed causal closed-loop experiments.Item Embargo Interrogating the role of hippocampal sharp-wave ripples in spontaneous learning(2023-10-26) Dutta, Shayok; Kemere, Caleb TRodents naturally explore novelty in contexts, objects, or locations, showing a preference for the unfamiliar. Lesion studies establish this novelty preference as dependent on the hippocampus, particularly through object recognition memory (ORM) paradigms. Recent research links hippocampal CA1 LFP signatures, including fast-gamma and beta-band oscillations, to object-place recognition memory. This work observes predictable increases in transient hippocampal events like sharp-wave ripples (SWRs). Although SWRs increase after encoding novelty, the associated spiking activity does not necessarily align with object-place pairings, raising questions about the role of SWRs in curiosity-driven spontaneous learning tasks. This thesis employs selective modulation of SWR activity using a previously engineered open-source, closed-loop SWR detection system in an ORM displaced object paradigm. Results reveal that suppressing SWR activity during object encoding and post-encoding rest sessions significantly impairs object-place recognition memory. Analysis of recorded CA1 LFP data shows statistical changes in SWR rates between disruption and control groups, while preserving general exploratory behavior across these groups. Further analysis correlates changes in SWR duration from pre-encoding to post-encoding rest sessions with discrimination measures. These correlations suggest that longer ripple durations lead to higher novelty preference scores. To investigate this phenomenon, the study employs a novel algorithm for the selective interrogation of longer-duration ripples during post-encoding rest sessions. In conclusion, the findings indicate that SWRs, particularly longer-duration ripples, critically influence object-place recognition memory driven by curiosity. This work advances our understanding of memory consolidation and the processing of spontaneous memories, extending beyond the traditionally studied realm of food or reward-driven spatial memories.