Knowledge-Driven Contrast Gain Control is Characterized by Two Distinct Electrocortical Markers

Sensitivity to variations in luminance (contrast) is fundamental to perception because contrasts define the edges and textures of visual objects. Recent research has shown that contrast sensitivity, in addition to being controlled by purely stimulus-driven mechanisms, is also affected by expectations and prior knowledge about the contrast of upcoming stimuli. The ability to adjust contrast sensitivity based on expectations and prior knowledge could help to maximize the information extracted when scanning familiar visual scenes. In the present study we used the event-related potentials (ERP) technique to resolve the stages that mediate knowledge-driven aspects of contrast gain control. Using groupwise independent components analysis and multivariate partial least squares, we isolated two robust spatiotemporal patterns of electrical brain activity associated with preparation for upcoming targets whose contrast was predicted by a cue. The patterns were sensitive to the informative value of the cue. When the cues were informative, these patterns were also able to differentiate among cues that predicted low-contrast targets and cues that predicted high-contrast targets. Both patterns were localized to parts of occipitotemporal cortex, and their morphology, latency, and topography resembled P2/N2 and P3 potentials. These two patterns provide electrophysiological markers of knowledge-driven preparation for impending changes in contrast and shed new light on the manner in which top-down factors modulate sensory processing

Functional Embedding Predicts the Variability of Neural Activity

Neural activity is irregular and unpredictable, yet little is known about why this is the case and how this property relates to the functional architecture of the brain. Here we show that the variability of a region’s activity systematically varies according to its topological role in functional networks. We recorded the resting-state electroencephalogram (EEG) and constructed undirected graphs of functional networks. We measured the centrality of each node in terms of the number of connections it makes (degree), the ease with which the node can be reached from other nodes in the network (efficiency) and the tendency of the node to occupy a position on the shortest paths between other pairs of nodes in the network (betweenness). As a proxy for variability, we estimated the information content of neural activity using multiscale entropy analysis. We found that the rate at which information was generated was largely predicted by centrality. Namely, nodes with greater degree, betweenness, and efficiency were more likely to have high information content, while peripheral nodes had relatively low information content. These results suggest that the variability of regional activity reflects functional embedding

Propofol sedation-induced alterations in brain connectivity reflect parvalbumin interneurone distribution in human cerebral cortex.

BACKGROUND: Propofol, a commonly used intravenous anaesthetic, binds to type A gamma aminobutyric acid (GABA) receptors in mammalian brain. Previous work on its anaesthetic action has characterised either the biochemistry underlying propofol binding or the associated changes in brain network dynamics during sedation. Despite these advances, no study has focused on understanding how propofol action at the cellular level results in changes in brain network connectivity. METHODS: We used human whole-brain microarray data to generate distribution maps for genes that mark the primary GABAergic cortical interneurone subtypes (somatostatin, parvalbumin [PV], and 5-hydroxytryptamine 3A. Next, 25 healthy participants underwent propofol-induced sedation during resting state functional MRI scanning. We used partial least squares analysis to identify the brain regions in which connectivity patterns were most impacted by propofol sedation. We then correlated these multimodal cortical patterns to determine if a specific interneurone subtype was disproportionately expressed in brain regions in which connectivity patterns were altered during sedation. RESULTS: Brain networks that were significantly altered by propofol sedation had a high density of PV-expressing GABAergic interneurones. Brain networks that anticorrelated during normal wakefulness, namely the default mode network and attentional and frontoparietal control networks, increased in correlation during sedation. CONCLUSIONS: PV-expressing interneurones are highly expressed in brain regions with altered connectivity profiles during propofol-induced sedation. This study also demonstrates the utility of leveraging multiple datasets to address multiscale neurobiological problems.This work was supported by a grant from the Wellcome Trust: Clinical Research Training Fellowship to RA.(Contract grant number: O8366O/Z/O7/Z); the National Institute for Health Research (NIHR, UK), Cambridge Biomedical Research Centre and NIHR Senior Investigator Awards to DKM; The Canadian Institute for Advanced Research (CIFAR) to DKM and EAS (RCZB/O72 RG93l93); the Stephen Erskine Fellowship (Queens' College, Cambridge) to EAS; the British Oxygen Professorship of the Royal College of Anaesthetists to DKM. MC was supported by the Cambridge International Trust and the Howard Sidney Sussex Research Studentship. IP was supported by Downing College, University of Cambridge through a Treherne Studentship; This work was also supported by the NIHR Brain Injury Healthcare Technology Co-operative based at Cambridge University Hospitals NHS Foundation Trust and University of Cambridge

Comparative Structural and Optical Properties of Different Ceria Nanoparticles

Herein a comparative study of five nanocrystalline cerium oxides (CeO2-delta) synthesised by different methods and calcined at 500 degrees C is reported. XRPD analysis showed that stoichiometry parameter delta, crystallite size/strain and lattice constant were only slightly affected by the method utilized. All ceria nanoparticles are nearly spherical in shape with faceted morphology, free of defects and with a relatively uniform size distribution. The average microstrain was found to be approximately 10 times higher than that of bulk counterpart. The absorption edge of nanocrystalline materials was shifted towards a higher wavelengths (red shift) in comparison with bulk counterpart, and band gap values were in the range 2.7-3.24 eV (3.33 eV for bulk counterpart)

Generative models of the human connectome

The human connectome represents a network map of the brain's wiring diagram and the pattern into which its connections are organized is thought to play an important role in cognitive function. The generative rules that shape the topology of the human connectome remain incompletely understood. Earlier work in model organisms has suggested that wiring rules based on geometric relationships (distance) can account for many but likely not all topological features. Here we systematically explore a family of generative models of the human connectome that yield synthetic networks designed according to different wiring rules combining geometric and a broad range of topological factors. We find that a combination of geometric constraints with a homophilic attachment mechanism can create synthetic networks that closely match many topological characteristics of individual human connectomes, including features that were not included in the optimization of the generative model itself. We use these models to investigate a lifespan dataset and show that, with age, the model parameters undergo progressive changes, suggesting a rebalancing of the generative factors underlying the connectome across the lifespan.Comment: 38 pages, 5 figures + 19 supplemental figures, 1 tabl

Material characterization of the main steam gate valve made of X20CrMoV 12.1 steel after long term service

Martensitic steel X20CrMo12.1 has been extensively used within the last few decades as a material for tubing systems and pipelines in thermal power plants (TPP). Long term behavior of this steel is very well known and understood and because of that was found to be reliable material for prolonged service at elevated temperatures. It is well known that during operation TPP components are subject to microstructural changes that inevitably reflect decrease in their mechanical properties that lead to the loss of structural integrity and serviceability of component. This paper deals with the comprehensive investigation carried out on the main steam gate valve parent material of welded joint, as a part of main steam pipeline, after 170.000 h of service (545 degrees C and 19MPa). The obtained results showed that the microstructural degradation caused by long term operation had little effects on the hardness and strength of material, while the changes in impact toughness were observed. Comprehensive microstructural analysis included the examination of the microstructure on the surface and trough the wall thickness

Material characterization of the main steam gate valve made of X20CrMoV 12.1 steel after long term service

Martensitic steel X20CrMo12.1 has been extensively used within the last few decades as a material for tubing systems and pipelines in thermal power plants (TPP). Long term behavior of this steel is very well known and understood and because of that was found to be reliable material for prolonged service at elevated temperatures. It is well known that during operation TPP components are subject to microstructural changes that inevitably reflect decrease in their mechanical properties that lead to the loss of structural integrity and serviceability of component. This paper deals with the comprehensive investigation carried out on the main steam gate valve parent material of welded joint, as a part of main steam pipeline, after 170.000 h of service (545 degrees C and 19MPa). The obtained results showed that the microstructural degradation caused by long term operation had little effects on the hardness and strength of material, while the changes in impact toughness were observed. Comprehensive microstructural analysis included the examination of the microstructure on the surface and trough the wall thickness

TWO STEP CURRENT INCREASES IN GLOW DISCHARGE DEVELOPMENT IN NEON FILLED DIODE AT 4 mbar

Abstract. The results are presented of investigating temporal and spatial development of electrical glow discharge in a neo

Distinct and dissociable EEG networks are associated with recovery of cognitive function following anesthesia-induced unconsciousness

The temporal trajectories and neural mechanisms of recovery of cognitive function after a major perturbation of consciousness is of both clinical and neuroscientific interest. The purpose of the present study was to investigate network-level changes in functional brain connectivity associated with the recovery and return of six cognitive functions after general anesthesia. High-density electroencephalograms (EEG) were recorded from healthy volunteers undergoing a clinically relevant anesthesia protocol (propofol induction and isoflurane maintenance), and age-matched healthy controls. A battery of cognitive tests (motor praxis, visual object learning test, fractal-2-back, abstract matching, psychomotor vigilance test, digital symbol substitution test) was administered at baseline, upon recovery of consciousness (ROC), and at half-hour intervals up to 3 h following ROC. EEG networks were derived using the strength of functional connectivity measured through the weighted phase lag index (wPLI). A partial least squares (PLS) analysis was conducted to assess changes in these networks: (1) between anesthesia and control groups; (2) during the 3-h recovery from anesthesia; and (3) for each cognitive test during recovery from anesthesia. Networks were maximally perturbed upon ROC but returned to baseline 30-60 min following ROC, despite deficits in cognitive performance that persisted up to 3 h following ROC. Additionally, during recovery from anesthesia, cognitive tests conducted at the same time-point activated distinct and dissociable functional connectivity networks across all frequency bands. The results highlight that the return of cognitive function after anesthetic-induced unconsciousness is task-specific, with unique behavioral and brain network trajectories of recovery

The Functional Connectivity Landscape of the Human Brain

Functional brain networks emerge and dissipate over a primarily static anatomical foundation. The dynamic basis of these networks is inter-regional communication involving local and distal regions. It is assumed that inter-regional distances play a pivotal role in modulating network dynamics. Using three different neuroimaging modalities, 6 datasets were evaluated to determine whether experimental manipulations asymmetrically affect functional relationships based on the distance between brain regions in human participants. Contrary to previous assumptions, here we show that short- and long-range connections are equally likely to strengthen or weaken in response to task demands. Additionally, connections between homotopic areas are the most stable and less likely to change compared to any other type of connection. Our results point to a functional connectivity landscape characterized by fluid transitions between local specialization and global integration. This ability to mediate functional properties irrespective of spatial distance may engender a diverse repertoire of cognitive processes when faced with a dynamic environment.</p