Cortical Gradients and Laminar Projections in Mammals Goulas, Alexandros; Zilles, Karl; Hilgetag, Claus C.
Trends in neurosciences (Regular ed.),
November 2018, 2018-11-00, 20181101, Letnik:
41, Številka:
11
Journal Article
Recenzirano
A key component of current theories of brain structure and function is the layer-specific origin of structural connections of the cerebral cortex. This fundamental connectional feature pertains to ...different mammalian cortices, and recent neuroimaging advancements have started to pave the way for its function-based mapping in humans. Here, we propose a framework that systematically explains the characteristic layer-specific origin of structural connections and its graded variation across the cortical sheet and across mammalian species. The framework unifies seemingly dispersed observations on multiple levels of cortical organization, including the cellular, connectional, and functional level. Moreover, the framework allows the prediction of the layer-specific origin of connections in a spectrum of mammals, from rodents to humans.
The laminar origin of cortico-cortical connections constitutes a key component of contemporary theories of brain structure and function.
Detailed mapping of the laminar origin of connections is experimentally feasible in non-human mammals using invasive methods.
Recent neuroimaging advancements pave the way for the functional mapping of cortico-cortical connections with laminar-specific resolution in humans.
A unifying framework for the graded laminar architecture of cortico-cortical connections across the cortical sheet and across mammalian species is lacking.
We highlight such a framework that exhibits explanatory and predictive power and links the different dimensions of cortical organization of mammals. This framework constitutes a basis for expanding our understanding of the multiple levels of architecture of the mammalian cerebral cortex.
Biological neuronal networks (BNNs) are a source of inspiration and analogy making for researchers that focus on artificial neuronal networks (ANNs). Moreover, neuroscientists increasingly use ANNs ...as a model for the brain. Despite certain similarities between these two types of networks, important differences can be discerned. First, biological neural networks are sculpted by evolution and the constraints that it entails, whereas artificial neural networks are engineered to solve particular tasks. Second, the network topology of these systems, apart from some analogies that can be drawn, exhibits pronounced differences. Here, we examine strategies to construct recurrent neural networks (RNNs) that instantiate the network topology of brains of different species. We refer to such RNNs as bio-instantiated. We investigate the performance of bio-instantiated RNNs in terms of: (i) the prediction performance itself, that is, the capacity of the network to minimize the cost function at hand in test data, and (ii) speed of training, that is, how fast during training the network reaches its optimal performance. We examine bio-instantiated RNNs in working memory tasks where task-relevant information must be tracked as a sequence of events unfolds in time. We highlight the strategies that can be used to construct RNNs with the network topology found in BNNs, without sacrificing performance. Despite that we observe no enhancement of performance when compared to randomly wired RNNs, our approach demonstrates how empirical neural network data can be used for constructing RNNs, thus, facilitating further experimentation with biologically realistic network topologies, in contexts where such aspect is desired.
•Constructing artificial neural networks with network topology of animal brains.•Network topology as a structural prior effecting performance of neural systems.•Framework for building neurobiologically realistic brain models.
The adult Drosophila midgut is maintained by intestinal stem cells (ISCs) that generate both self-renewing and differentiating daughter cells. How this asymmetry is generated is currently unclear. ...Here, we demonstrate that asymmetric ISC division is established by a unique combination of extracellular and intracellular polarity mechanisms. We show that Integrin-dependent adhesion to the basement membrane induces cell-intrinsic polarity and results in the asymmetric segregation of the Par proteins Par-3, Par-6, and aPKC into the apical daughter cell. Cell-specific knockdown and overexpression experiments suggest that increased activity of aPKC enhances Delta/Notch signaling in one of the two daughter cells to induce terminal differentiation. Perturbing this mechanism or altering the orientation of ISC division results in the formation of intestinal tumors. Our data indicate that mechanisms for intrinsically asymmetric cell division can be adapted to allow for the flexibility in lineage decisions that is required in adult stem cells.
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► Par complex segregates asymmetrically in dividing Drosophila intestinal stem cells ► Par complex inhibition leads to tumor-like intestinal stem cell overproliferation ► aPKC overactivation alters levels of Notch activity, causing stem cell loss ► Integrins regulate spindle orientation and Par protein localization
This paper extends the role of Par proteins in asymmetric cell division to an adult stem cell lineage—the Drosophila intestinal stem cell—and implicates integrins in regulating Par asymmetry in this context.
Condensation reactions such as Guerbet and aldol are important since they allow for C–C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on ...hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO.
Remote sensing of solar-induced chlorophyll fluorescence (SIF) is a rapidly advancing front in terrestrial vegetation science, with emerging capability in space-based methodologies and diverse ...application prospects. Although remote sensing of SIF – especially from space – is seen as a contemporary new specialty for terrestrial plants, it is founded upon a multi-decadal history of research, applications, and sensor developments in active and passive sensing of chlorophyll fluorescence. Current technical capabilities allow SIF to be measured across a range of biological, spatial, and temporal scales. As an optical signal, SIF may be assessed remotely using high-resolution spectral sensors in tandem with state-of-the-art algorithms to distinguish the emission from reflected and/or scattered ambient light. Because the red to far-red SIF emission is detectable non-invasively, it may be sampled repeatedly to acquire spatio-temporally explicit information about photosynthetic light responses and steady-state behaviour in vegetation. Progress in this field is accelerating with innovative sensor developments, retrieval methods, and modelling advances. This review distills the historical and current developments spanning the last several decades. It highlights SIF heritage and complementarity within the broader field of fluorescence science, the maturation of physiological and radiative transfer modelling, SIF signal retrieval strategies, techniques for field and airborne sensing, advances in satellite-based systems, and applications of these capabilities in evaluation of photosynthesis and stress effects. Progress, challenges, and future directions are considered for this unique avenue of remote sensing.
•Historical and current progress in remote sensing of SIF are reviewed.•Technical capabilities allow measurements over a range of spatial scales.•Sensor capabilities, retrieval methods, and modelling are now quite advanced.•Applications in vegetation include stress detection and photosynthesis.•Future directions include validation, optimized systems, and interpretation.
The goal of this study was to explore the potential of carob extracts to act as lipid inhibitors in model food systems. First, the extraction efficacy of fourteen solvents on the phenolic and ...flavonoid contents as well as on the antioxidant activity was assessed. Results showed that the phenolic composition and antioxidant activity of the extracts were strongly affected by solvents. Subsequently, the antioxidant potential of the most promising extracts (water, methanol, acidic acetone, and acetone-water) against four model food systems were evaluated. The acidic acetone extract had the highest antioxidant activity (70.3 ± 5.3%) in the β-carotene-linoleic acid system, followed by the acetone-water extract (62.1 ± 4.9%). Both extracts significantly prevented the lipid oxidation in sunflower oil and cooked comminuted pork; the inhibition activity at the end of storage period was 36.7-50.5% and 17.4-24.8%, respectively. A reduction of 49.5-54.8% in the formation of dienes in the oil-in-water emulsion was also found. The inhibitory effect of methanolic and aqueous extracts was significantly lower. Qualitative and quantitative variations in extracts are responsible for this antioxidant behavior in food systems. Gallic acid, myrecetin, rutin, and catechin are the main components of the extracts while myricetin and quercetin play an essential role in the antioxidant activity, according to the biochromatograms.
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•Microstructural features of a thick-walled WAAM stainless steel part are investigated.•Microstructure exhibits periodically repeating characteristics across the WAAM part.•Oriented ...and textured structure with large grains at the overlapping region of adjacent fusion zones.•Significant spatial variations in terms of fusion zone shape, grain structure, texture, and phases.
Wire arc additive manufacturing (WAAM) is a class of technologies suitable for producing large parts due to its high material deposition and building rates. Among the many possible materials processed by WAAM, austenitic stainless steels, e.g. 316L, are commonly employed. The structure of WAAM 316L thin parts has been studied extensively before. However, multiwalled or thick WAAM 316L parts remain largely unexplored. Hence, in this study, the microstructure of a thick 316LSi WAAM part is characterised in detail. The microstructure of the part consists of large and highly-oriented columnar grains dominated by epitaxial and competitive growth. The overlapping regions between neighbouring fusion zones contain long grains with a dominant texture, which cross several layers and are aligned with the building direction. The grains' internal microstructure consists of an austenite matrix, ferrite with locally varying dendritic morphologies and dispersed oxide inclusions. The texture spatially varies across the part, and this variation is correlated to the local thermal gradient induced by the building strategy and processing conditions used during the manufacturing of the thick-walled part.
Selective laser melting is a promising additive manufacturing technology for manufacturing porous metallic bone scaffolds. Bone repair requires scaffolds that meet various mechanical and biological ...requirements. This paper addresses this challenge by comprehensively studying the performance of porous scaffolds. The main novelty is exploring scaffolds with different porosities, verifying various aspects of their performance and revealing the effect of their permeability on cell growth. This study evaluates the manufacturability, mechanical behaviour, permeability and biocompatibility of gyroid scaffolds. In simulations, mechanical behaviour and permeability exhibited up to 56% and 73% accuracy, respectively, compared to the experimental data. The compression and permeability experiments showed that the elastic modulus and the permeability of the scaffolds were both in the range of human bones. The morphological experiment showed that manufacturing accuracy increased with greater designed porosity, while the in vitro experiments revealed that permeability played the main role in cell proliferation. The significance of this work is improving the understanding of the effect of design parameters on the mechanical properties, permeability and cell growth of the scaffolds, which will enable the design of porous bone scaffolds with better bone-repair effects.
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•Proposing a design method to improve the accuracy of manufactured porosity of high-porosity scaffolds.•Comprehensively studying the manufacturability, mechanical and mass transport properties, and biocompatibility of gyroid scaffolds.•The simulation of the mechanical and mass-transport properties of scaffolds both showed predictability.•Greater pore size gave bone scaffolds higher permeability, which promotes bone repair•The factors possibly affecting the prediction accuracy of the mechanical and mass-transport properties of lattice scaffolds were summarised.
Quantifying global photosynthesis remains a challenge due to a lack of accurate remote sensing proxies. Solar-induced chlorophyll fluorescence (SIF) has been shown to be a good indicator of ...photosynthetic activity across various spatial scales. However, a global and spatially challenging estimate of terrestrial gross primary production (GPP) based on satellite SIF remains unresolved due to the confounding effects of species-specific physical and physiological traits and external factors, such as canopy structure or photosynthetic pathway (C3 or C4). Here we analyze an ensemble of far-red SIF data from OCO-2 satellite and ground observations at multiple sites, using the spectral invariant theory to reduce the effects of canopy structure and to retrieve a structure-corrected total canopy SIF emission (SIFtotal). We find that the relationships between observed canopy-leaving SIF and ecosystem GPP vary significantly among biomes. In contrast, the relationships between SIFtotal and GPP converge around two unique models, one for C3 and one for C4 plants. We show that the two single empirical models can be used to globally scale satellite SIF observations to terrestrial GPP. We obtain an independent estimate of global terrestrial GPP of 129.56 ± 6.54 PgC/year for the 2015–2017 period, which is consistent with the state-of-the-art data- and process-oriented models. The new GPP product shows improved sensitivity to previously undetected ‘hotspots’ of productivity, being able to resolve the double-peak in GPP due to rotational cropping systems. We suggest that the direct scheme to estimate GPP presented here, which is based on satellite SIF, may open up new possibilities to resolve the dynamics of global terrestrial GPP across space and time.
•An ensemble of far-red SIF from ground and OCO-2 was compared with in situ GPP.•BRF data can be used to reduce the effects of canopy structure on SIF.•BRF data is used to derive total canopy SIF emission (SIFtotal) for OCO-2.•SIFtotal and GPP relationships converge two unique models for C3 and C4 plants.•SIFtotal-based model yields an estimate of GPP of 129.56 PgC/year for 2015–2017.
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