La physiopathologie de la céphalée migraineuse a été pendant des siècles attribuée exclusivement à la vasodilatation des artères intra- et extracrâniennes. Récemment, la controverse a amené à ...s’interroger sur la migraine en tant que maladie neuronale avec peu ou pas de rôle de la vasodilatation dans la douleur. Dans la première partie de cette controverse, nous faisons état des arguments cliniques, thérapeutiques, en doppler et en imagerie fonctionnelle par angiographie par résonance magnétique (ARM), faisant état d’une vasodilatation des artères intra- et extracrâniennes mais qui est au final modeste, puisque de l’ordre de 12 % dans les dernières études en ARM avec crises déclenchées pharmacologiquement par le CGRP.
The role of vasodilatation in migraine pathophysiology is still debated with three hypotheses. The first is that vasodilatation of meningeal or intracranial arteries are the primary cause of pain. The second is that vasodilatation is secondary to neuronal activation, but can sustain or increase pain through sensitized perivascular nociceptors. The third is that vasodilatation is an epiphenomenon neither sufficient nor necessary for pain. We review in this part the arguments in favor of the old hypothesis that vasodilation is the primary cause of pain. Finally we show that there is a mild vasodilation during the attacks provoked by CGRP infusion.
Migraine with aura Lucas, C.
Revue neurologique,
September 2021, 2021-09-00, 20210901, Letnik:
177, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Around 15% to one-third of migraineurs experience aura. Aura is a fully reversible focal neurological phenomenon involving visual, sensory, speech, and/or motor symptoms that develops gradually and ...usually precedes the headache phase. The pivotal role of cortical spreading depression (CSD) as a mechanism underlying aura has been widely supported by a large body of studies. The diagnosis is based on the International Headache Classification Disorders III edition criteria. Aura is characterized by gradual development, duration of each symptom no longer than one hour, a mix of positive and negative features, and complete reversibility. Visual aura is the most common type of aura, occurring in over 90% of patients. When aura symptoms are multiple, they usually follow one another in succession, beginning with visual, then sensory, then aphasic; but the reverse and other orders have been noted. The accepted duration for most aura symptoms is one hour, but motor symptoms, which are rare, are often longer lasting. When a patient experiences for the first time a possible aura phase it's sometimes difficult to know if there was gradual or brutal onset of the symptoms. If the patient has no visual aura symptoms or simultaneous neurological symptoms, or presents neurological symptoms corresponding to a cerebral vascular territory, emergency exploration of a possible transient ischemic attack is necessary. Long duration (greater than one hour) of what may or may not be an aura phase, late onset of aura, or a dramatic increase in aura attacks should also be explored. The relative risk of ischemic stroke is significantly increased in migraine with aura. Combined hormonal contraception with estrogens significantly increases the risk of stroke in women with migraine with aura. It is recommended to start non-steroidal anti-inflammatory drugs (NSAIDs) or aspirin as soon as possible during the aura phase, not to treat the aura, but to avoid or to diminish the headache phase. In case of failure of NSAIDs or aspirin it is recommended to use a triptan when the headache begins. The prophylactic treatments for migraine with aura are those used in migraine without aura based on very few randomized clinical trials specifically dedicated to migraine with aura.
Background
It is well established that the functioning of terrestrial ecosystems depends on biophysical and biogeochemical feedbacks occurring at the soil-plant-atmosphere (SPA) interface. However, ...dynamic biophysical and biogeochemical processes that operate at local scales are seldom studied in conjunction with structural ecosystem properties that arise from broad environmental constraints. As a result, the effect of SPA interactions on how ecosystems respond to, and exert influence on, the global environment remains difficult to predict.
Scope
We review recent findings that link structural and functional SPA interactions and evaluate their potential for predicting ecosystem responses to chronic environmental pressures. Specifically, we propose a quantitative framework for the integrated analysis of three major plant functional groups (evergreen conifers, broadleaf deciduous, and understory shrubs) and their distinct mycorrhizal symbionts under rising levels of carbon dioxide, changing climate, and disturbance regime. First, we explain how symbiotic and competitive strategies involving plants and soil microorganisms influence scale-free patterns of carbon, nutrient, and water use from individual organisms to landscapes. We then focus on the relationship between those patterns and structural traits such as specific leaf area, leaf area index, and soil physical and chemical properties that constrain root connectivity and canopy gas exchange. Finally, we use those relationships to predict how changes in ecosystem structure may affect processes that are important for climate stability.
Conclusions
On the basis of emerging ecological theory and empirical biophysical and biogeochemical knowledge, we propose ten interpretive hypotheses that serve as a primary set of hierarchical relationships (or scaling rules), by which local SPA interactions can be spatially and temporally aggregated to inform broad climate change mitigation efforts. To this end, we provide a series of numerical formulations that simplify the net outcome of complex SPA interactions as a first step towards anticipating shifts in terrestrial carbon, water, and nutrient cycles.
In source localization of electroencephalograpic (EEG) signals, as well as in targeted transcranial electric current stimulation (tES), a volume conductor model is required to describe the flow of ...electric currents in the head. Boundary element models (BEM) can be readily computed to represent major tissue compartments, but cannot encode detailed anatomical information within compartments. Finite element models (FEM) can capture more tissue types and intricate anatomical structures, but with the higher precision also comes the need for semi-automated segmentation, and a higher computational cost. In either case, adjusting to the individual human anatomy requires costly magnetic resonance imaging (MRI), and thus head modeling is often based on the anatomy of an ‘arbitrary’ individual (e.g. Colin27). Additionally, existing reference models for the human head often do not include the cerebro-spinal fluid (CSF), and their field of view excludes portions of the head and neck—two factors that demonstrably affect current-flow patterns. Here we present a highly detailed FEM, which we call ICBM-NY, or "New York Head". It is based on the ICBM152 anatomical template (a non-linear average of the MRI of 152 adult human brains) defined in MNI coordinates, for which we extended the field of view to the neck and performed a detailed segmentation of six tissue types (scalp, skull, CSF, gray matter, white matter, air cavities) at 0.5mm3 resolution. The model was solved for 231 electrode locations. To evaluate its performance, additional FEMs and BEMs were constructed for four individual subjects. Each of the four individual FEMs (regarded as the ‘ground truth’) is compared to its BEM counterpart, the ICBM-NY, a BEM of the ICBM anatomy, an ‘individualized’ BEM of the ICBM anatomy warped to the individual head surface, and FEMs of the other individuals. Performance is measured in terms of EEG source localization and tES targeting errors. Results show that the ICBM-NY outperforms FEMs of mismatched individual anatomies as well as the BEM of the ICBM anatomy according to both criteria. We therefore propose the New York Head as a new standard head model to be used in future EEG and tES studies whenever an individual MRI is not available. We release all model data online at neuralengr.com/nyhead/ to facilitate broad adoption.
•Individual head models for EEG source imaging and tCS stimulation are computationally expensive.•Instead, we propose a highly detailed standardized FEM model of the ICBM152 non-linear average head defined on MNI coordinates.•We approximate 4 individual heads and measure localization and targeting errors.•Our model compares favorably to individual and individualized models.•All data are made available.
Generalized Geometric Quantum Speed Limits Pires, Diego Paiva; Cianciaruso, Marco; Céleri, Lucas C. ...
Physical review. X,
06/2016, Letnik:
6, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The attempt to gain a theoretical understanding of the concept of time in quantum mechanics has triggered significant progress towards the search for faster and more efficient quantum technologies. ...One of such advances consists in the interpretation of the time-energy uncertainty relations as lower bounds for the minimal evolution time between two distinguishable states of a quantum system, also known as quantum speed limits. We investigate how the nonuniqueness of a bona fide measure of distinguishability defined on the quantum-state space affects the quantum speed limits and can be exploited in order to derive improved bounds. Specifically, we establish an infinite family of quantum speed limits valid for unitary and nonunitary evolutions, based on an elegant information geometric formalism. Our work unifies and generalizes existing results on quantum speed limits and provides instances of novel bounds that are tighter than any established one based on the conventional quantum Fisher information. We illustrate our findings with relevant examples, demonstrating the importance of choosing different information metrics for open system dynamics, as well as clarifying the roles of classical populations versus quantum coherences, in the determination and saturation of the speed limits. Our results can find applications in the optimization and control of quantum technologies such as quantum computation and metrology, and might provide new insights in fundamental investigations of quantum thermodynamics.
A translucent box Lucas, Tim C. D.
Ecological monographs,
November 2020, Letnik:
90, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Machine learning has become popular in ecology but its use has remained restricted to predicting, rather than understanding, the natural world. Many researchers consider machine learning algorithms ...to be a black box. These models can, however, with careful examination, be used to inform our understanding of the world. They are translucent boxes. Furthermore, the interpretation of these models can be an important step in building confidence in a model or in a specific prediction from a model. Here I review a number of techniques for interpreting machine learning models at the level of the system, the variable, and the individual prediction as well as methods for handling non-independent data. I also discuss the limits of interpretability for different methods and demonstrate these approaches using a case example of understanding litter sizes in mammals.
Fire shapes the distribution of savanna and forest through complex interactions involving climate, resources and species traits. Based on data from central Brazil, we propose that these interactions ...are governed by two critical thresholds. The fire‐resistance threshold is reached when individual trees have accumulated sufficient bark to avoid stem death, whereas the fire‐suppression threshold is reached when an ecosystem has sufficient canopy cover to suppress fire by excluding grasses. Surpassing either threshold is dependent upon long fire‐free intervals, which are rare in mesic savanna. On high‐resource sites, the thresholds are reached quickly, increasing the probability that savanna switches to forest, whereas low‐resource sites are likely to remain as savanna even if fire is infrequent. Species traits influence both thresholds; saplings of savanna trees accumulate bark thickness more quickly than forest trees, and are more likely to become fire resistant during fire‐free intervals. Forest trees accumulate leaf area more rapidly than savanna trees, thereby accelerating the transition to forest. Thus, multiple factors interact with fire to determine the distribution of savanna and forest by influencing the time needed to reach these thresholds. Future work should decipher multiple environmental controls over the rates of tree growth and canopy closure in savanna.
Objective. Research in the area of transcranial electrical stimulation (TES) often relies on computational models of current flow in the brain. Models are built based on magnetic resonance images ...(MRI) of the human head to capture detailed individual anatomy. To simulate current flow on an individual, the subject's MRI is segmented, virtual electrodes are placed on this anatomical model, the volume is tessellated into a mesh, and a finite element model (FEM) is solved numerically to estimate the current flow. Various software tools are available for each of these steps, as well as processing pipelines that connect these tools for automated or semi-automated processing. The goal of the present tool-realistic volumetric-approach to simulate transcranial electric simulation (ROAST)-is to provide an end-to-end pipeline that can automatically process individual heads with realistic volumetric anatomy leveraging open-source software and custom scripts to improve segmentation and execute electrode placement. Approach. ROAST combines the segmentation algorithm of SPM12, a Matlab script for touch-up and automatic electrode placement, the finite element mesher iso2mesh and the solver getDP. We compared its performance with commercial FEM software, and SimNIBS, a well-established open-source modeling pipeline. Main results. The electric fields estimated with ROAST differ little from the results obtained with commercial meshing and FEM solving software. We also do not find large differences between the various automated segmentation methods used by ROAST and SimNIBS. We do find bigger differences when volumetric segmentation are converted into surfaces in SimNIBS. However, evaluation on intracranial recordings from human subjects suggests that ROAST and SimNIBS are not significantly different in predicting field distribution, provided that users have detailed knowledge of SimNIBS. Significance. We hope that the detailed comparisons presented here of various choices in this modeling pipeline can provide guidance for future tool development. We released ROAST as an open-source, easy-to-install and fully-automated pipeline for individualized TES modeling.
(ProQuest: ... denotes formulae/symbols omitted.)The authors present scalable algorithms for parallel adaptive mesh refinement and coarsening (AMR), partitioning, and 2:1 balancing on computational ...domains composed of multiple connected two-dimensional quadtrees or three-dimensional octrees, referred to as a forest of octrees. By distributing the union of octants from all octrees in parallel, they combine the high scalability proven previously for adaptive single-octree algorithms with the geometric flexibility that can be achieved by arbitrarily connected hexahedral macromeshes, in which each macroelement is the root of an adapted octree. A key concept of their approach is an encoding scheme of the interoctree connectivity that permits arbitrary relative orientations between octrees. They demonstrate the parallel scalability of p4est on its own and in combination with two geophysics codes. Using p4est they generate and adapt multioctree meshes with up to 5.13 x ... octants on as many as 220,320 CPU cores and execute the 2:1 balance algorithm in less than 10 seconds per million octants per process.
PDF
