General anesthesia reduces complexity and temporal asymmetry of the informational structures derived from neural recordings in Drosophila

We apply techniques from the field of computational mechanics to evaluate the statistical complexity of neural recording data from fruit flies. First, we connect statistical complexity to the flies' level of conscious arousal, which is manipulated by general anesthesia (isoflurane). We show that the complexity of even single channel time series data decreases under anesthesia. The observed difference in complexity between the two states of conscious arousal increases as higher orders of temporal correlations are taken into account. We then go on to show that, in addition to reducing complexity, anesthesia also modulates the informational structure between the forward- and reverse-time neural signals. Specifically, using three distinct notions of temporal asymmetry we show that anesthesia reduces temporal asymmetry on information-theoretic and information-geometric grounds. In contrast to prior work, our results show that: (1) Complexity differences can emerge at very short timescales and across broad regions of the fly brain, thus heralding the macroscopic state of anesthesia in a previously unforeseen manner, and (2) that general anesthesia also modulates the temporal asymmetry of neural signals. Together, our results demonstrate that anesthetized brains become both less structured and more reversible.Comment: 14 pages, 6 figures. Comments welcome; Added time-reversal analysis, updated discussion, new figures (Fig. 5 & Fig. 6) and Tables (Tab. 1

A Multi-Layered Study on Harmonic Oscillations in Mammalian Genomics and Proteomics

Cellular, organ, and whole animal physiology show temporal variation predominantly featuring 24-h (circadian) periodicity. Time-course mRNA gene expression profiling in mouse liver showed two subsets of genes oscillating at the second (12-h) and third (8-h) harmonic of the prime (24-h) frequency. The aim of our study was to identify specific genomic, proteomic, and functional properties of ultradian and circadian subsets. We found hallmarks of the three oscillating gene subsets, including different (i) functional annotation, (ii) proteomic and electrochemical features, and (iii) transcription factor binding motifs in upstream regions of 8-h and 12-h oscillating genes that seemingly allow the link of the ultradian gene sets to a known circadian network. Our multifaceted bioinformatics analysis of circadian and ultradian genes suggests that the different rhythmicity of gene expression impacts physiological outcomes and may be related to transcriptional, translational and post-translational dynamics, as well as to phylogenetic and evolutionary components

Aeronautical Engineering: A continuing bibliography with indexes, supplement 99

This bibliography lists 292 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1978

A Role for Hippocampal Sharp-wave Ripples in Active Visual Search

Sharp-wave ripples (SWRs) in the hippocampus are thought to contribute to memory formation, though this effect has only been demonstrated in rodents. The SWR, a large deflection in the hippocampal LFP (local field potential), is known to occur primarily during slow wave sleep and during immobility and consummator behaviors. SWRs have widespread effects throughout the cortex, and are directly implicated in memory formation their occurrence correlates with correct performance, and their ablation impairs memory in spatial memory tasks. Though SWRs have been reported in primates, their role is poorly understood. Whether or not SWRs play a role in memory formation, as they do in rodents, has yet to be confirmed. This work encompasses three separate studies with the goal of determining whether there is a link between SWR occurrence and memory formation in the macaque. Chapter 2 establishes the validity of the modified Change Blindness task as a memory task which is sensitive to normal hippocampal function in monkeys. Chapter 3 establishes that SWR events occur during waking (and stationary) activity, during visual search, in the macaque. Until this work, the prevalence of SWRs in macaques during waking exploration was unknown. Chapter 4 shows that gaze during SWRs was more likely to be near the target object on repeated than on novel presentations, even after accounting for overall differences in gaze location with scene repetition. The increase in ripple likelihood near remembered visual objects suggests a link between ripples and memory in primates; specifically, SWRs may reflect part of a mechanism supporting the guidance of search based on experience. The amalgamation of this work reveals several novel findings and establishes an important step towards understanding the role that SWRs play in memory formation in predominantly-visual primate brains