The temporal and bilateral structure of hippocampal replay

Thesis (Ph. D. in Neuroscience)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.The hippocampus is required for the formation, but not storage, of long-term episodic memories. During memory formation, however, the hippocampus is not a lone actor; rather it works in concert with various structures across the brain. The mechanisms by which diverse populations of cells are coordinated for the formation of a single, coherent memory remain unknown. This thesis is an investigation of the temporal and hemispheric structure of replay events. The timing of replay is investigated at the levels of hippocampal sharp-wave ripples and multi-unit activity. We found that, during sleep, ripples generation is modulated by a 10-15Hz rhythm. We also observed this rhythm in the multi-unit firing rate of hippocampal neurons. Next we investigated and quantified the level of coordination between the hippocampal during replay events. Using bilateral hippocampal recordings from several rats during spatial navigation and subsequent sleep epochs, we directly compared the activity of these two spatially isolated networks at the level of the local field potential and the information encoded by the two neuronal populations. We found that the neural activity of the two hippocampi was highly correlated in some aspects but not others. As previously reported in the mouse, we found that, in the rat, sharp-wave ripples were simultaneously generated spontaneously in both hippocampi and that, although the intrinsic frequencies of ripple oscillations were correlated bilaterally, the phases of the individual ripple wavelets were not. Finally, we found that information encoded by both hippocampal ensembles is highly correlated during replay events.by Stuart Pope Layton.Ph.D.in Neuroscienc

Increasing frailty is associated with higher prevalence and reduced recognition of delirium in older hospitalised inpatients: results of a multi-centre study

Purpose: Delirium is a neuropsychiatric disorder delineated by an acute change in cognition, attention, and consciousness. It is common, particularly in older adults, but poorly recognised. Frailty is the accumulation of deficits conferring an increased risk of adverse outcomes. We set out to determine how severity of frailty, as measured using the CFS, affected delirium rates, and recognition in hospitalised older people in the United Kingdom. Methods: Adults over 65 years were included in an observational multi-centre audit across UK hospitals, two prospective rounds, and one retrospective note review. Clinical Frailty Scale (CFS), delirium status, and 30-day outcomes were recorded. Results: The overall prevalence of delirium was 16.3% (483). Patients with delirium were more frail than patients without delirium (median CFS 6 vs 4). The risk of delirium was greater with increasing frailty [OR 2.9 (1.8–4.6) in CFS 4 vs 1–3; OR 12.4 (6.2–24.5) in CFS 8 vs 1–3]. Higher CFS was associated with reduced recognition of delirium (OR of 0.7 (0.3–1.9) in CFS 4 compared to 0.2 (0.1–0.7) in CFS 8). These risks were both independent of age and dementia. Conclusion: We have demonstrated an incremental increase in risk of delirium with increasing frailty. This has important clinical implications, suggesting that frailty may provide a more nuanced measure of vulnerability to delirium and poor outcomes. However, the most frail patients are least likely to have their delirium diagnosed and there is a significant lack of research into the underlying pathophysiology of both of these common geriatric syndromes

Transductive neural decoding for unsorted neuronal spikes of rat hippocampus

Neural decoding is an important approach for extracting information from population codes. We previously proposed a novel transductive neural decoding paradigm and applied it to reconstruct the rat's position during navigation based on unsorted rat hippocampal ensemble spiking activity. Here, we investigate several important technical issues of this new paradigm using one data set of one animal. Several extensions of our decoding method are discussed.National Institutes of Health (U.S.) (NIH Grant DP1-OD003646)National Institutes of Health (U.S.) (NIH Grant MH061976