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1
Umar, A., S. Ahmad e T. K. Datta. "Stability Analysis of a Moored Vessel". Journal of Offshore Mechanics and Arctic Engineering 126, n. 2 (1 maggio 2004): 164–74. http://dx.doi.org/10.1115/1.1710873.
Testo completoAbstract (sommario):
A procedure for the stability analysis of a slack mooring system is presented for periodic wave excitation by finding its approximate response using a two term harmonic balance method (HBM). The conditions for determining the local and global stability of the approximate solutions are established using Hill’s variational approach and Floquet’s theory. A number of instability phenomena are identified for the mooring system for certain frequencies of excitations which fall outside the range of frequencies obtained from the analytically derived stability boundaries. The instability phenomena include symmetry breaking bifurcation, subharmonics, 3T and 5T solutions. Even chaotic motion is exhibited under certain cases.
2
Hamaguchi, Kosuke, Alexa Riehle e Nicolas Brunel. "Estimating Network Parameters From Combined Dynamics of Firing Rate and Irregularity of Single Neurons". Journal of Neurophysiology 105, n. 1 (gennaio 2011): 487–500. http://dx.doi.org/10.1152/jn.00858.2009.
Testo completoAbstract (sommario):
High firing irregularity is a hallmark of cortical neurons in vivo, and modeling studies suggest a balance of excitation and inhibition is necessary to explain this high irregularity. Such a balance must be generated, at least partly, from local interconnected networks of excitatory and inhibitory neurons, but the details of the local network structure are largely unknown. The dynamics of the neural activity depends on the local network structure; this in turn suggests the possibility of estimating network structure from the dynamics of the firing statistics. Here we report a new method to estimate properties of the local cortical network from the instantaneous firing rate and irregularity (CV2) under the assumption that recorded neurons are a part of a randomly connected sparse network. The firing irregularity, measured in monkey motor cortex, exhibits two features; many neurons show relatively stable firing irregularity in time and across different task conditions; the time-averaged CV2 is widely distributed from quasi-regular to irregular (CV2 = 0.3–1.0). For each recorded neuron, we estimate the three parameters of a local network [balance of local excitation-inhibition, number of recurrent connections per neuron, and excitatory postsynaptic potential (EPSP) size] that best describe the dynamics of the measured firing rates and irregularities. Our analysis shows that optimal parameter sets form a two-dimensional manifold in the three-dimensional parameter space that is confined for most of the neurons to the inhibition-dominated region. High irregularity neurons tend to be more strongly connected to the local network, either in terms of larger EPSP and inhibitory PSP size or larger number of recurrent connections, compared with the low irregularity neurons, for a given excitatory/inhibitory balance. Incorporating either synaptic short-term depression or conductance-based synapses leads many low CV2 neurons to move to the excitation-dominated region as well as to an increase of EPSP size.
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Mariño, Jorge, James Schummers, David C. Lyon, Lars Schwabe, Oliver Beck, Peter Wiesing, Klaus Obermayer e Mriganka Sur. "Invariant computations in local cortical networks with balanced excitation and inhibition". Nature Neuroscience 8, n. 2 (23 gennaio 2005): 194–201. http://dx.doi.org/10.1038/nn1391.
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Zheng, Ying, Jing Jing Luo, Sam Harris, Aneurin Kennerley, Jason Berwick, Steve A. Billings e John Mayhew. "Balanced excitation and inhibition: Model based analysis of local field potentials". NeuroImage 63, n. 1 (ottobre 2012): 81–94. http://dx.doi.org/10.1016/j.neuroimage.2012.06.040.
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Lattuada, Enrico, Stefano Buzzaccaro e Roberto Piazza. "Thermophoresis in self-associating systems: probing poloxamer micellization by opto-thermal excitation". Soft Matter 15, n. 10 (2019): 2140–51. http://dx.doi.org/10.1039/c8sm02386g.
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Renart, Alfonso, Rubén Moreno-Bote, Xiao-Jing Wang e Néstor Parga. "Mean-Driven and Fluctuation-Driven Persistent Activity in Recurrent Networks". Neural Computation 19, n. 1 (gennaio 2007): 1–46. http://dx.doi.org/10.1162/neco.2007.19.1.1.
Testo completoAbstract (sommario):
Spike trains from cortical neurons show a high degree of irregularity, with coefficients of variation (CV) of their interspike interval (ISI) distribution close to or higher than one. It has been suggested that this irregularity might be a reflection of a particular dynamical state of the local cortical circuit in which excitation and inhibition balance each other. In this “balanced” state, the mean current to the neurons is below threshold, and firing is driven by current fluctuations, resulting in irregular Poisson-like spike trains. Recent data show that the degree of irregularity in neuronal spike trains recorded during the delay period of working memory experiments is the same for both low-activity states of a few Hz and for elevated, persistent activity states of a few tens of Hz. Since the difference between these persistent activity states cannot be due to external factors coming from sensory inputs, this suggests that the underlying network dynamics might support coexisting balanced states at different firing rates. We use mean field techniques to study the possible existence of multiple balanced steady states in recurrent networks of current-based leaky integrate-and-fire (LIF) neurons. To assess the degree of balance of a steady state, we extend existing mean-field theories so that not only the firing rate, but also the coefficient of variation of the interspike interval distribution of the neurons, are determined self-consistently. Depending on the connectivity parameters of the network, we find bistable solutions of different types. If the local recurrent connectivity is mainly excitatory, the two stable steady states differ mainly in the mean current to the neurons. In this case, the mean drive in the elevated persistent activity state is suprathreshold and typically characterized by low spiking irregularity. If the local recurrent excitatory and inhibitory drives are both large and nearly balanced, or even dominated by inhibition, two stable states coexist, both with subthreshold current drive. In this case, the spiking variability in both the resting state and the mnemonic persistent state is large, but the balance condition implies parameter fine-tuning. Since the degree of required fine-tuning increases with network size and, on the other hand, the size of the fluctuations in the afferent current to the cells increases for small networks, overall we find that fluctuation-driven persistent activity in the very simplified type of models we analyze is not a robust phenomenon. Possible implications of considering more realistic models are discussed.
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Wang, Jiang, Ruixue Han, Xilei Wei, Yingmei Qin, Haitao Yu e Bin Deng. "Weak signal detection and propagation in diluted feed-forward neural network with recurrent excitation and inhibition". International Journal of Modern Physics B 30, n. 02 (20 gennaio 2016): 1550253. http://dx.doi.org/10.1142/s0217979215502537.
Testo completoAbstract (sommario):
Reliable signal propagation across distributed brain areas provides the basis for neural circuit function. Modeling studies on cortical circuits have shown that multilayered feed-forward networks (FFNs), if strongly and/or densely connected, can enable robust signal propagation. However, cortical networks are typically neither densely connected nor have strong synapses. This paper investigates under which conditions spiking activity can be propagated reliably across diluted FFNs. Extending previous works, we model each layer as a recurrent sub-network constituting both excitatory (E) and inhibitory (I) neurons and consider the effect of interactions between local excitation and inhibition on signal propagation. It is shown that elevation of cellular excitation–inhibition (EI) balance in the local sub-networks (layers) softens the requirement for dense/strong anatomical connections and thereby promotes weak signal propagation in weakly connected networks. By means of iterated maps, we show how elevated local excitability state compensates for the decreased gain of synchrony transfer function that is due to sparse long-range connectivity. Finally, we report that modulations of EI balance and background activity provide a mechanism for selectively gating and routing neural signal. Our results highlight the essential role of intrinsic network states in neural computation.
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Anticevic, Alan, e John Lisman. "How Can Global Alteration of Excitation/Inhibition Balance Lead to the Local Dysfunctions That Underlie Schizophrenia?" Biological Psychiatry 81, n. 10 (maggio 2017): 818–20. http://dx.doi.org/10.1016/j.biopsych.2016.12.006.
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Brunel, Nicolas, e Xiao-Jing Wang. "What Determines the Frequency of Fast Network Oscillations With Irregular Neural Discharges? I. Synaptic Dynamics and Excitation-Inhibition Balance". Journal of Neurophysiology 90, n. 1 (luglio 2003): 415–30. http://dx.doi.org/10.1152/jn.01095.2002.
Testo completoAbstract (sommario):
When the local field potential of a cortical network displays coherent fast oscillations (∼40-Hz gamma or ∼200-Hz sharp-wave ripples), the spike trains of constituent neurons are typically irregular and sparse. The dichotomy between rhythmic local field and stochastic spike trains presents a challenge to the theory of brain rhythms in the framework of coupled oscillators. Previous studies have shown that when noise is large and recurrent inhibition is strong, a coherent network rhythm can be generated while single neurons fire intermittently at low rates compared to the frequency of the oscillation. However, these studies used too simplified synaptic kinetics to allow quantitative predictions of the population rhythmic frequency. Here we show how to derive quantitatively the coherent oscillation frequency for a randomly connected network of leaky integrate-and-fire neurons with realistic synaptic parameters. In a noise-dominated interneuronal network, the oscillation frequency depends much more on the shortest synaptic time constants (delay and rise time) than on the longer synaptic decay time, and ∼200-Hz frequency can be realized with synaptic time constants taken from slice data. In a network composed of both interneurons and excitatory cells, the rhythmogenesis is a compromise between two scenarios: the fast purely interneuronal mechanism, and the slower feedback mechanism (relying on the excitatory-inhibitory loop). The properties of the rhythm are determined essentially by the ratio of time scales of excitatory and inhibitory currents and by the balance between the mean recurrent excitation and inhibition. Faster excitation than inhibition, or a higher excitation/inhibition ratio, favors the feedback loop and a much slower oscillation (typically in the gamma range).
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Jenkins, Edward B. "A Thermal Pressure Inside the Local Bubble, as Revealed by CI Fine-Structure Excitation". International Astronomical Union Colloquium 166 (1997): 33–36. http://dx.doi.org/10.1017/s0252921100070676.
Testo completoAbstract (sommario):
AbstractUltraviolet absorption lines from carbon atoms within a neutral cloud inside or near the edge of the Local Bubble can reveal the thermal pressure of the gas, since the relative populations of the fine-structure levels are determined by a balance between collisional excitation and radiative decay. Features from a C I multiplet appearing in the uv spectrum of the star δ Cyg (l = 79°, b = +10°, d = 52 pc) were observed with the echelle spectrograph of the Goddard High Resolution Spectrograph on HST. An interpretation of absorptions detected from the two lowest levels gives a thermal pressure range 102.7 < p/k < 103.7 cm−3K.
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Ueda, Ken-Ichi. "Present status and prospect of KrF laser physics and technology–large volume excitation and UV optics". Laser and Particle Beams 7, n. 3 (agosto 1989): 375–82. http://dx.doi.org/10.1017/s0263034600007333.
Testo completoAbstract (sommario):
The physics and technology for e-beam generation, large volume excitation and the ultra-violet optics for high power KrF lasers is presented. The potential, due to the charge deposition, induces a return current in the plasma which balances the e-beam current. The local equilibrium mechanism stabilizes the large volume excitation using intense electron beams. The spatial and temporal characteristics of large aperture diodes are analyzed. Substantial progress in ultra violet optics in Japan has been achieved. The damage threshold of HR dielectric coating increases up to 11 J/cm2 by using low absorption materials.
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Lowe, B. "The role of Ca2+ in deflection-induced excitation of motile, mechanoresponsive balancer cilia in the ctenophore statocyst." Journal of Experimental Biology 200, n. 11 (1 giugno 1997): 1593–606. http://dx.doi.org/10.1242/jeb.200.11.1593.
Testo completoAbstract (sommario):
Motile, mechanoresponsive cilia (balancers) in ctenophore statocysts, like vertebrate hair cells, are excited or inhibited depending upon the direction in which they are deflected. Balancers, however, may become either excited (beat rapidly) or inhibited (beat slowly) by deflection in the same direction, depending on the sign of ctenophore geotaxis (positive or negative). The beat frequency of many cilia is controlled by concentrations of Ca2+, membrane potential and neural input. How these factors affect deflection-induced ciliary beating in balancers was investigated. Deflection-induced excitation of balancers in whole Mnemiopsis leidyi larvae and dissected adult (Mnemiopsis leidyi, Pleurobrachia pileus) statocysts was reversibly inhibited by the Ca2+ channel inhibitors Co2+, Mg2+, Ni2+, and Mn2+. Deflection-induced excitation in balancers of isolated adult M. leidyi balancer groups was also inhibited by Co2+ or by Ca(2+)-free medium. Isolated balancer group cilia, like balancer cilia of intact ctenophores, exhibited responses to either sign of geotaxis and graded responses to deflection. Isolated balancers that were chemically depolarized in high-[K+], Ca(2+)-free medium were excited by local application of Ca2+ onto the ciliary bases, but not onto the cell bases or the ciliary tips. It is proposed that deflection-induced excitation of balancers is due to influx of Ca2+ through stretch- and voltage-activated channel activity. The sign of geotaxis of whole larvae and dissected adult statocysts was switched by electrical stimulation. Thus, neural input may participate in reversing the directional sensitivity of balancer cells.
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Vattikonda, Anirudh, Bapi Raju Surampudi, Arpan Banerjee, Gustavo Deco e Dipanjan Roy. "Does the regulation of local excitation–inhibition balance aid in recovery of functional connectivity? A computational account". NeuroImage 136 (agosto 2016): 57–67. http://dx.doi.org/10.1016/j.neuroimage.2016.05.002.
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Hu, Xiaoyu, Evan Chodora, Saurabh Prabhu, Akshay Gupte e Sez Atamturktur. "Model calibration of locally nonlinear dynamical systems". Engineering Computations 36, n. 2 (11 marzo 2019): 466–90. http://dx.doi.org/10.1108/ec-10-2017-0419.
Testo completoAbstract (sommario):
PurposeThis paper aims to present an approach for calibrating the numerical models of dynamical systems that have spatially localized nonlinear components. The approach implements the extended constitutive relation error (ECRE) method using multi-harmonic coefficients and is conceived to separate the errors in the representation of the global, linear and local, nonlinear components of the dynamical system through a two-step process.Design/methodology/approachThe first step focuses on the system’s predominantly linear dynamic response under a low magnitude periodic excitation. In this step, the discrepancy between measured and predicted multi-harmonic coefficients is calculated in terms of residual energy. This residual energy is in turn used to spatially locate errors in the model, through which one can identify the erroneous model inputs which govern the linear behavior that need to be calibrated. The second step involves measuring the system’s nonlinear dynamic response under a high magnitude periodic excitation. In this step, the response measurements under both low and high magnitude excitation are used to iteratively calibrate the identified linear and nonlinear input parameters.FindingsWhen model error is present in both linear and nonlinear components, the proposed iterative combined multi-harmonic balance method (MHB)-ECRE calibration approach has shown superiority to the conventional MHB-ECRE method, while providing more reliable calibration results of the nonlinear parameter with less dependency ona prioriknowledge of the associated linear system.Originality/valueThis two-step process is advantageous as it reduces the confounding effects of the uncertain model parameters associated with the linear and locally nonlinear components of the system.
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Fu, Xinghe, Dingyu Guo, Kai Hou, Hongchao Zhu, Wu Chen e Da Xu. "Fault Diagnosis of an Excitation System Using a Fuzzy Neural Network Optimized by a Novel Adaptive Grey Wolf Optimizer". Processes 12, n. 9 (20 settembre 2024): 2032. http://dx.doi.org/10.3390/pr12092032.
Testo completoAbstract (sommario):
As the excitation system is the core control component of a synchronous condenser system, its fault diagnosis is crucial for maximizing the reactive power compensation capability of the synchronous condenser. To achieve accurate diagnosis of excitation system faults, this paper proposes a novel adaptive grey wolf optimizer (AGWO) to optimize the initial weights and biases of the fuzzy neural network (FNN), thereby enhancing the diagnostic performance of the FNN model. Firstly, an improved nonlinear convergence factor is introduced to balance the algorithm’s global exploration and local exploitation capabilities. Secondly, a new adaptive position update strategy that enhances the interaction capability of the position information is proposed to improve the algorithm’s ability to jump out of the local optimum and accelerate the convergence speed. In addition, it is demonstrated that the proposed AGWO algorithm has global convergence. By selecting real fault waveforms of the excitation system for case validation, the results show that the proposed AGWO has a better convergence performance compared to the grey wolf optimizer (GWO), particle swarm optimization (PSO), whale optimization algorithm (WOA), and marine predator algorithm (MPA). Specifically, compared to the FNN and GWO-FNN models, the AGWO-FNN model improves average diagnostic accuracy on the test set by 4.2% and 2.5%, respectively. Therefore, the proposed AGWO-FNN effectively enhances the accuracy of fault diagnosis in the excitation system and exhibits stronger diagnostic capability.
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Ekelmans, Pierre, Nataliya Kraynyukovas e Tatjana Tchumatchenko. "Targeting operational regimes of interest in recurrent neural networks". PLOS Computational Biology 19, n. 5 (15 maggio 2023): e1011097. http://dx.doi.org/10.1371/journal.pcbi.1011097.
Testo completoAbstract (sommario):
Neural computations emerge from local recurrent neural circuits or computational units such as cortical columns that comprise hundreds to a few thousand neurons. Continuous progress in connectomics, electrophysiology, and calcium imaging require tractable spiking network models that can consistently incorporate new information about the network structure and reproduce the recorded neural activity features. However, for spiking networks, it is challenging to predict which connectivity configurations and neural properties can generate fundamental operational states and specific experimentally reported nonlinear cortical computations. Theoretical descriptions for the computational state of cortical spiking circuits are diverse, including the balanced state where excitatory and inhibitory inputs balance almost perfectly or the inhibition stabilized state (ISN) where the excitatory part of the circuit is unstable. It remains an open question whether these states can co-exist with experimentally reported nonlinear computations and whether they can be recovered in biologically realistic implementations of spiking networks. Here, we show how to identify spiking network connectivity patterns underlying diverse nonlinear computations such as XOR, bistability, inhibitory stabilization, supersaturation, and persistent activity. We establish a mapping between the stabilized supralinear network (SSN) and spiking activity which allows us to pinpoint the location in parameter space where these activity regimes occur. Notably, we find that biologically-sized spiking networks can have irregular asynchronous activity that does not require strong excitation-inhibition balance or large feedforward input and we show that the dynamic firing rate trajectories in spiking networks can be precisely targeted without error-driven training algorithms.
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Nguyen, Bao N., Allison M. McKendrick e Algis J. Vingrys. "Abnormal inhibition-excitation imbalance in migraine". Cephalalgia 36, n. 1 (18 marzo 2015): 5–14. http://dx.doi.org/10.1177/0333102415576725.
Testo completoAbstract (sommario):
Background People with migraine show increased surround suppression of perceived contrast, a perceptual analogue of centre-surround antagonistic interactions in visual cortex. A proposed mechanism is that cortical ‘hyperexcitability’ or ‘hyperresponsivity’, a prominent theory in the migraine literature, drives abnormal excitatory-inhibitory balance to give increased local inhibition. The purpose of this cross-sectional study was to determine whether cortical hyperresponsivity and excitatory-inhibitory imbalance manifests in the visual cortical response of migraine sufferers. Methods Interictal steady-state visual evoked potentials (VEPs) in response to 0 to 97% contrast were recorded in 30 migraine participants (15 without aura, 15 with aura) and 21 non-headache controls. Monotonicity indices were calculated to determine response saturation or supersaturation. Contrast gain was modelled with a modified saturating hyperbolic function to allow for variation in excitation and inhibition. Results A greater proportion of migraine participants (43%) than controls (14%) exhibited significant VEP supersaturation at high contrast, based on monotonicity index (chi-square, p = 0.028). Supersaturation was also evident by the trend for greater suppressive exponent values in migraine compared to control individuals (Mann-Whitney rank sum, p = 0.075). Conclusions Supersaturation in migraine is consistent with excess excitation (hyperresponsivity) driving increased network inhibition and provides support for excitatory-inhibitory imbalance as a pathophysiological disturbance in migraine.
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Linster, Christiane, e Claudine Masson. "A Neural Model of Olfactory Sensory Memory in the Honeybee's Antennal Lobe". Neural Computation 8, n. 1 (gennaio 1996): 94–114. http://dx.doi.org/10.1162/neco.1996.8.1.94.
Testo completoAbstract (sommario):
We present a neural model for olfactory sensory memory in the honeybee's antennal lobe. To investigate the neural mechanisms underlying odor discrimination and memorization, we exploit a variety of morphological, physiological, and behavioral data. The model allows us to study the computational capacities of the known neural circuitry, and to interpret under a new light experimental data on the cellular as well as on the neuronal assembly level. We propose a scheme for memorization of the neural activity pattern after stimulus offset by changing the local balance between excitation and inhibition. This modulation is achieved by changing the intrinsic parameters of local inhibitory neurons or synapses.
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Busche, Marc Aurel, e Arthur Konnerth. "Impairments of neural circuit function in Alzheimer's disease". Philosophical Transactions of the Royal Society B: Biological Sciences 371, n. 1700 (5 agosto 2016): 20150429. http://dx.doi.org/10.1098/rstb.2015.0429.
Testo completoAbstract (sommario):
An essential feature of Alzheimer's disease (AD) is the accumulation of amyloid-β (Aβ) peptides in the brain, many years to decades before the onset of overt cognitive symptoms. We suggest that during this very extended early phase of the disease, soluble Aβ oligomers and amyloid plaques alter the function of local neuronal circuits and large-scale networks by disrupting the balance of synaptic excitation and inhibition ( E / I balance) in the brain. The analysis of mouse models of AD revealed that an Aβ-induced change of the E / I balance caused hyperactivity in cortical and hippocampal neurons, a breakdown of slow-wave oscillations, as well as network hypersynchrony. Remarkably, hyperactivity of hippocampal neurons precedes amyloid plaque formation, suggesting that hyperactivity is one of the earliest dysfunctions in the pathophysiological cascade initiated by abnormal Aβ accumulation. Therapeutics that correct the E / I balance in early AD may prevent neuronal dysfunction, widespread cell loss and cognitive impairments associated with later stages of the disease. This article is part of the themed issue ‘Evolution brings Ca 2+ and ATP together to control life and death’.
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Sammon, M. "Geometry of respiratory phase switching". Journal of Applied Physiology 77, n. 5 (1 novembre 1994): 2468–80. http://dx.doi.org/10.1152/jappl.1994.77.5.2468.
Testo completoAbstract (sommario):
A second-order ordinary differential equation is outlined for the temporal dynamics of the respiratory central pattern generator (RCPG). Recurrent interactions between central excitation and inhibition confine the breathing cycle to the interior of a heteroclinic orbit between switching points (saddle equilibria) located at end expiration (E-I) and end inspiration (I-E). Dynamics depend on four eigenvalues that control inspiratory drive (lambda), excitability of inspiratory off switch (omega 1; stage 1 expiration), rate of central excitation disinhibition (omega 2; stage 2 expiration), and damping of the oscillator (epsilon). Ratios omega 2/lambda and omega 1/lambda determine local E-I and I-E phase switching, whereas inspiratory-to-expiratory balance varies as omega 2/(lambda omega 1). Stable apnea is seen when (lambda omega 2)/epsilon is near zero; inspiratory apneusis is seen when (lambda omega 1)/epsilon is low. The equations provide formalisms for discussing phase switching, apneas, apneuses, phase resetting and singularities, rapid shallow breathing, postinhibitory rebound excitation, redundancy, gating within the RCPG, and behavioral control of breathing. The model is offered as an explicit alternative to the harmonic oscillator models that have been used in the past to describe RCPG function.
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Liu, Sensen, e ShiNung Ching. "Recurrent Information Optimization with Local, Metaplastic Synaptic Dynamics". Neural Computation 29, n. 9 (settembre 2017): 2528–52. http://dx.doi.org/10.1162/neco_a_00993.
Testo completoAbstract (sommario):
We consider the problem of optimizing information-theoretic quantities in recurrent networks via synaptic learning. In contrast to feedforward networks, the recurrence presents a key challenge insofar as an optimal learning rule must aggregate the joint distribution of the whole network. This challenge, in particular, makes a local policy (i.e., one that depends on only pairwise interactions) difficult. Here, we report a local metaplastic learning rule that performs approximate optimization by estimating whole-network statistics through the use of several slow, nested dynamical variables. These dynamics provide the rule with both anti-Hebbian and Hebbian components, thus allowing for decorrelating and correlating learning regimes that can occur when either is favorable for optimality. We demonstrate the performance of the synthesized rule in comparison to classical BCM dynamics and use the networks to conduct history-dependent tasks that highlight the advantages of recurrence. Finally, we show the consistency of the resultant learned networks with notions of criticality, including balanced ratios of excitation and inhibition.
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Brenet, Alexandre, Rahma Hassan-Abdi, Julie Somkhit, Constantin Yanicostas e Nadia Soussi-Yanicostas. "Defective Excitatory/Inhibitory Synaptic Balance and Increased Neuron Apoptosis in a Zebrafish Model of Dravet Syndrome". Cells 8, n. 10 (4 ottobre 2019): 1199. http://dx.doi.org/10.3390/cells8101199.
Testo completoAbstract (sommario):
Dravet syndrome is a type of severe childhood epilepsy that responds poorly to current anti-epileptic drugs. In recent years, zebrafish disease models with Scn1Lab sodium channel deficiency have been generated to seek novel anti-epileptic drug candidates, some of which are currently undergoing clinical trials. However, the spectrum of neuronal deficits observed following Scn1Lab depletion in zebrafish larvae has not yet been fully explored. To fill this gap and gain a better understanding of the mechanisms underlying neuron hyperexcitation in Scn1Lab-depleted larvae, we analyzed neuron activity in vivo using combined local field potential recording and transient calcium uptake imaging, studied the distribution of excitatory and inhibitory synapses and neurons as well as investigated neuron apoptosis. We found that Scn1Lab-depleted larvae displayed recurrent epileptiform seizure events, associating massive synchronous calcium uptakes and ictal-like local field potential bursts. Scn1Lab-depletion also caused a dramatic shift in the neuronal and synaptic balance toward excitation and increased neuronal death. Our results thus provide in vivo evidence suggesting that Scn1Lab loss of function causes neuron hyperexcitation as the result of disturbed synaptic balance and increased neuronal apoptosis.
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Dai, Chao-Qing, Guo-quan Zhou e Jie-Fang Zhang. "Exotic Localized Structures of the (2+1)-Dimensional Nizhnik-Novikov- Veselov System Obtained via the Extended Homogeneous Balance Method". Zeitschrift für Naturforschung A 61, n. 5-6 (1 giugno 2006): 216–24. http://dx.doi.org/10.1515/zna-2006-5-602.
Testo completoAbstract (sommario):
In this paper, we successfully apply the extended homogeneous balance method (EHBM) to derive a new type of variable separation solutions for the (2+1)-dimensional Nizhnik-Novikov-Veselov system. Novel localized coherent structures about multi-valued functions, i.e., special dromion, special peakon and foldon, and the interactions among them are discussed. Moreover, the explicit phase shifts for all the local excitations offered by the quantity U are given and applied to novel interactions among special dromion, special peakon and foldon in detail. - PACS numbers: 05.45.Yv, 02.30.Jr, 02.03Ik
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Schönfelder, V., V. A. Dogiel, M. J. Freyberg e G. E. Morfill. "Low Energy Cosmic Rays Emitted by the Orion Complex into the Local Medium". International Astronomical Union Colloquium 166 (1997): 187–90. http://dx.doi.org/10.1017/s0252921100070950.
Testo completoAbstract (sommario):
AbstractThe excess of γ-ray emission in the energy range 3–7 MeV discovered by COMPTEL in the direction of the Orion complex may imply that there is a powerful source of low energy cosmic rays in the local galactic medium. Several interpretations of the excess have been suggested. One of them assumes that the emission is identified with nuclear de-excitation lines of excited 16O and 14C. To provide the excess the energy deposit in these nuclei should be as large as ~ 1039 erg s−1. If a comparable part of these nuclei escape into the local galactic medium they can play a significant role in the energy balance there.If the excess is interpreted as continuous it can be produced by bremsstrahlung emission of fast 10 MeV electrons. Much less energy deposit in these electrons is necessary (~ 1036 erg s−1) to generate the observed Orion flux. The intensity of these electrons even near Earth can be higher than that of the galactic cosmic ray electrons.
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Xue, Beirao, Jixin Man, Yanfeng Zuo e Wengao Yan. "Vibration Response Analysis of a Time-varying Stiffness Wheel with Contrate Gear under Unbalanced Excitation". Journal of Physics: Conference Series 2694, n. 1 (1 gennaio 2024): 012063. http://dx.doi.org/10.1088/1742-6596/2694/1/012063.
Testo completoAbstract (sommario):
Abstract The vibration and response of multi-contact interface micro-motion time-varying stiffness wheel are analyzed, and the nonlinear vibration response characteristics caused by the unbalance force of multi-contact interface contrate gear face of a gas turbine rotor are studied. Firstly, the local sliding model of dry friction-damped contact is extended to establish a holistic and local unified sliding model. The equivalent stiffness and damping of the damping device are calculated by means of the equivalent linearization method and the first harmonic balance method. Finally, the finite element model of multi-contact contrate gear rotor wheel is established to analyze the influence of different unbalanced masses on vibration response under nonlinear frictional contact. The results show that the response caused by the unbalance mass of multi-contact interface wheel with contrate gear is mainly radial response, and the peak value of resonance response increases with the increase of unbalance force.
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Harris, Kameron Decker, Tatiana Dashevskiy, Joshua Mendoza, Alfredo J. Garcia, Jan-Marino Ramirez e Eric Shea-Brown. "Different roles for inhibition in the rhythm-generating respiratory network". Journal of Neurophysiology 118, n. 4 (1 ottobre 2017): 2070–88. http://dx.doi.org/10.1152/jn.00174.2017.
Testo completoAbstract (sommario):
Unraveling the interplay of excitation and inhibition within rhythm-generating networks remains a fundamental issue in neuroscience. We use a biophysical model to investigate the different roles of local and long-range inhibition in the respiratory network, a key component of which is the pre-Bötzinger complex inspiratory microcircuit. Increasing inhibition within the microcircuit results in a limited number of out-of-phase neurons before rhythmicity and synchrony degenerate. Thus unstructured local inhibition is destabilizing and cannot support the generation of more than one rhythm. A two-phase rhythm requires restructuring the network into two microcircuits coupled by long-range inhibition in the manner of a half-center. In this context, inhibition leads to greater stability of the two out-of-phase rhythms. We support our computational results with in vitro recordings from mouse pre-Bötzinger complex. Partial excitation block leads to increased rhythmic variability, but this recovers after blockade of inhibition. Our results support the idea that local inhibition in the pre-Bötzinger complex is present to allow for descending control of synchrony or robustness to adverse conditions like hypoxia. We conclude that the balance of inhibition and excitation determines the stability of rhythmogenesis, but with opposite roles within and between areas. These different inhibitory roles may apply to a variety of rhythmic behaviors that emerge in widespread pattern-generating circuits of the nervous system. NEW & NOTEWORTHY The roles of inhibition within the pre-Bötzinger complex (preBötC) are a matter of debate. Using a combination of modeling and experiment, we demonstrate that inhibition affects synchrony, period variability, and overall frequency of the preBötC and coupled rhythmogenic networks. This work expands our understanding of ubiquitous motor and cognitive oscillatory networks.
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Siewe Siewe, M., F. M. Moukam Kakmeni, C. Tchawoua e P. Woafo. "Nonlinear Response and Suppression of Chaos by Weak Harmonic Perturbation Inside a Triple Well Φ6-Rayleigh Oscillator Combined to Parametric Excitations". Journal of Computational and Nonlinear Dynamics 1, n. 3 (15 febbraio 2006): 196–204. http://dx.doi.org/10.1115/1.2198215.
Testo completoAbstract (sommario):
The nonlinear response and suppression of chaos by weak harmonic perturbation inside a triple well Φ6-Rayleigh oscillator combined to parametric excitations is studied in this paper. The main attention is focused on the dynamical properties of local bifurcations as well as global bifurcations including homoclinic and heteroclinic bifurcations. The original oscillator is transformed to averaged equations using the method of harmonic balance to obtain periodic solutions. The response curves show the saddle-node bifurcation and the multi-stability phenomena. Based on the Melnikov’s method, horseshoe chaos is found and its control is made by introducing an external periodic perturbation.
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Esser, Steve K., Sean Hill e Giulio Tononi. "Breakdown of Effective Connectivity During Slow Wave Sleep: Investigating the Mechanism Underlying a Cortical Gate Using Large-Scale Modeling". Journal of Neurophysiology 102, n. 4 (ottobre 2009): 2096–111. http://dx.doi.org/10.1152/jn.00059.2009.
Testo completoAbstract (sommario):
Effective connectivity between cortical areas decreases during slow wave sleep. This decline can be observed in the reduced interareal propagation of activity evoked either directly in cortex by transcranial magnetic stimulation (TMS) or by sensory stimulation. We present here a large-scale model of the thalamocortical system that is capable of reproducing these experimental observations. This model was constructed according to a large number of physiological and anatomical constraints and includes over 30,000 spiking neurons interconnected by more than 5 million synaptic connections and organized into three cortical areas. By simulating the different effects of arousal promoting neuromodulators, the model can produce a waking or a slow wave sleep-like mode. In this work, we also seek to explain why intercortical signal transmission decreases in slow wave sleep. The traditional explanation for reduced brain responses during this state, a thalamic gate, cannot account for the reduced propagation between cortical areas. Therefore we propose that a cortical gate is responsible for this diminished intercortical propagation. We used our model to test three candidate mechanisms that might produce a cortical gate during slow wave sleep: a propensity to enter a local down state following perturbation, which blocks the propagation of activity to other areas, increases in potassium channel conductance that reduce neuronal responsiveness, and a shift in the balance of synaptic excitation and inhibition toward inhibition, which decreases network responses to perturbation. Of these mechanisms, we find that only a shift in the balance of synaptic excitation and inhibition can account for the observed in vivo response to direct cortical perturbation as well as many features of spontaneous sleep.
29
Yu, Dong, Tianyu Li, Qianming Ding, Yong Wu, Ziying Fu, Xuan Zhan, Lijian Yang e Ya Jia. "Maintenance of delay-period activity in working memory task is modulated by local network structure". PLOS Computational Biology 20, n. 9 (3 settembre 2024): e1012415. http://dx.doi.org/10.1371/journal.pcbi.1012415.
Testo completoAbstract (sommario):
Revealing the relationship between neural network structure and function is one central theme of neuroscience. In the context of working memory (WM), anatomical data suggested that the topological structure of microcircuits within WM gradient network may differ, and the impact of such structural heterogeneity on WM activity remains unknown. Here, we proposed a spiking neural network model that can replicate the fundamental characteristics of WM: delay-period neural activity involves association cortex but not sensory cortex. First, experimentally observed receptor expression gradient along the WM gradient network is reproduced by our network model. Second, by analyzing the correlation between different local structures and duration of WM activity, we demonstrated that small-worldness, excitation-inhibition balance, and cycle structures play crucial roles in sustaining WM-related activity. To elucidate the relationship between the structure and functionality of neural networks, structural circuit gradients in brain should also be subject to further measurement. Finally, combining anatomical data, we simulated the duration of WM activity across different brain regions, its maintenance relies on the interaction between local and distributed networks. Overall, network structural gradient and interaction between local and distributed networks are of great significance for WM.
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Kravchenko, Denis S., Elena V. Kustova e Maksim Yu Melnik. "Higher criteria for the regularity of a one-dimensional local field". Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy 9, n. 3 (2022): 426–39. http://dx.doi.org/10.21638/spbu01.2022.304.
Testo completoAbstract (sommario):
A coupled problem of gasdynamics, vibrational relaxation, and dissociation in the flow of oxygen behind reflected shock waves is studied. The detailed state-to-state kinetic approach is used, which is based on a coupled solution of the momentum and energy conservation equations with the balance equations for molecular vibrational state populations and concentrations of oxygen atoms. Initial conditions corresponding to recent experiments in shock tubes are considered. For different models of physicochemical processes, a comparison is made with experimental data; varying the model parameters yields satisfactory agreement of all gas-dynamic parameters with the measured ones. The key feature of the proposed approach is the allowance for partial vibrational-chemical relaxation in the time interval between the incident and reflected shock waves. When relaxation between the shocks is not frozen, the reflected shock wave propagates through a vibrationally nonequilibrium gas, which significantly affects kinetics and gas dynamics. Accounting for partial relaxation ensures good agreement between the pressure calculated behind the front of the reflected shock wave and the pressure measured in the experiment. On the other hand, comparison with the vibrational temperature calculated indirectly from spectroscopic experimental data under the assumption of frozen relaxation shows noticeable differences near the shock wave front. We conclude that the technique for extracting gas-dynamic parameters fromspectroscopic data has to be improved by taking into account vibrational excitation before the reflected shock wave.
31
Ostroverkhov, Mykola Yakovych, Vadim Volodymyrovych Chumack, Yevhen Andriovich Monakhov e Bogdan Ivanovych Pryymak. "Information supply of the power control system of the synchronous generator of the autonomous wind unit". Herald of Advanced Information Technology 4, n. 3 (15 ottobre 2021): 255–67. http://dx.doi.org/10.15276/hait.03.2021.5.
Testo completoAbstract (sommario):
This paper deals with information supply of automatic maximum power control system of synchronous hybrid excited genera-tor for the autonomous wind unit. The power supply system based on an autonomous wind turbine consists of an electric generator, a battery charging controller, a battery pack and an inverter, which provides the required frequency and valueof the consumer's supply voltage.Three phase permanent magnet synchronous generator that have high technical and economic indicators are most widely used as electric generator of autonomous wind turbines.The main disadvantage of these generators is the lack of effectivemethods of magnetic flux control, limiting the optimization of the energy balance of the wind turbine.The paper discusses the application of synchronous generator with hybrid excitation system that consists of permanent magnets and additional field excitation winding lo-cated on the stator. Mathematical model of a hybrid excited synchronous generator is presented. Also,an output maximum power control system in a case of wind speed change by varying field excitation current is developed. Control system is developed based on concept of reverse task of dynamics in combination with minimization of local functionals of instantaneous values of energies.In the basics of the control method is put an idea of the reversibility of the Lyapunov direct method for the stability analysis.Obtained con-trol law provides thesystem stability inwhole, which allows solving control tasks of interrelated objects via mathematical models of local loops. Control law also provides low sensitiveness to parametric disturbances and gives dynamic decomposition of interrelated non linear system that ensures its practical implementation. The study of the proposed power control system based on parameters of hybrid excited synchronous generator experimental sample has been carried out. The graphs of transient process of armature power, voltage and current in a case of wind speed change from 3 to 8 m/s were obtained, as well as in a case of active resistance load change. The results of study showed high efficiency of power control of a wind turbine with hybrid excited synchronous generator
32
Bergemann, Maria, Andrew J. Gallagher, Philipp Eitner, Manuel Bautista, Remo Collet, Svetlana A. Yakovleva, Anja Mayriedl et al. "Observational constraints on the origin of the elements". Astronomy & Astrophysics 631 (23 ottobre 2019): A80. http://dx.doi.org/10.1051/0004-6361/201935811.
Testo completoAbstract (sommario):
Manganese (Mn) is a key Fe-group element, commonly employed in stellar population and nucleosynthesis studies to explore the role of SN Ia. We have developed a new non-local thermodynamic equilibrium (NLTE) model of Mn, including new photo-ionisation cross-sections and new transition rates caused by collisions with H and H− atoms. We applied the model in combination with one-dimensional (1D) LTE model atmospheres and 3D hydrodynamical simulations of stellar convection to quantify the impact of NLTE and convection on the line formation. We show that the effects of NLTE are present in Mn I and, to a lesser degree, in Mn II lines, and these increase with metallicity and with the effective temperature of a model. Employing 3D NLTE radiative transfer, we derive a new abundance of Mn in the Sun, A(Mn) = 5.52 ± 0.03 dex, consistent with the element abundance in C I meteorites. We also applied our methods to the analysis of three metal-poor benchmark stars. We find that 3D NLTE abundances are significantly higher than 1D LTE. For dwarfs, the differences between 1D NLTE and 3D NLTE abundances are typically within 0.15 dex, however, the effects are much larger in the atmospheres of giants owing to their more vigorous convection. We show that 3D NLTE successfully solves the ionisation and excitation balance for the RGB star HD 122563 that cannot be achieved by 1D LTE or 1D NLTE modelling. For HD 84937 and HD 140283, the ionisation balance is satisfied, however, the resonance Mn I triplet lines still show somewhat lower abundances compared to the high-excitation lines. Our results for the benchmark stars confirm that 1D LTE modelling leads to significant systematic biases in Mn abundances across the full wavelength range from the blue to the IR. We also produce a list of Mn lines that are not significantly biased by 3D and can be reliably, within the 0.1 dex uncertainty, modelled in 1D NLTE.
33
Shirhatti, Vinay, Poojya Ravishankar e Supratim Ray. "Gamma oscillations in primate primary visual cortex are severely attenuated by small stimulus discontinuities". PLOS Biology 20, n. 6 (14 giugno 2022): e3001666. http://dx.doi.org/10.1371/journal.pbio.3001666.
Testo completoAbstract (sommario):
Gamma oscillations (30 to 80 Hz) have been hypothesized to play an important role in feature binding, based on the observation that continuous long bars induce stronger gamma in the visual cortex than bars with a small gap. Recently, many studies have shown that natural images, which have discontinuities in several low-level features, do not induce strong gamma oscillations, questioning their role in feature binding. However, the effect of different discontinuities on gamma has not been well studied. To address this, we recorded spikes and local field potential from 2 monkeys while they were shown gratings with discontinuities in 4 attributes: space, orientation, phase, or contrast. We found that while these discontinuities only had a modest effect on spiking activity, gamma power drastically reduced in all cases, suggesting that gamma could be a resonant phenomenon. An excitatory–inhibitory population model with stimulus-tuned recurrent inputs showed such resonant properties. Therefore, gamma could be a signature of excitation–inhibition balance, which gets disrupted due to discontinuities.
34
Pfeffer, Thomas, Adrian Ponce-Alvarez, Konstantinos Tsetsos, Thomas Meindertsma, Christoffer Julius Gahnström, Ruud Lucas van den Brink, Guido Nolte, Andreas Karl Engel, Gustavo Deco e Tobias Hinrich Donner. "Circuit mechanisms for the chemical modulation of cortex-wide network interactions and behavioral variability". Science Advances 7, n. 29 (luglio 2021): eabf5620. http://dx.doi.org/10.1126/sciadv.abf5620.
Testo completoAbstract (sommario):
Influential theories postulate distinct roles of catecholamines and acetylcholine in cognition and behavior. However, previous physiological work reported similar effects of these neuromodulators on the response properties (specifically, the gain) of individual cortical neurons. Here, we show a double dissociation between the effects of catecholamines and acetylcholine at the level of large-scale interactions between cortical areas in humans. A pharmacological boost of catecholamine levels increased cortex-wide interactions during a visual task, but not rest. An acetylcholine boost decreased interactions during rest, but not task. Cortical circuit modeling explained this dissociation by differential changes in two circuit properties: the local excitation-inhibition balance (more strongly increased by catecholamines) and intracortical transmission (more strongly reduced by acetylcholine). The inferred catecholaminergic mechanism also predicted noisier decision-making, which we confirmed for both perceptual and value-based choice behavior. Our work highlights specific circuit mechanisms for shaping cortical network interactions and behavioral variability by key neuromodulatory systems.
35
Bergemann, Maria, Aldo Serenelli e Gregory Ruchti. "Spectroscopic distances to late-type stars". Proceedings of the International Astronomical Union 8, S289 (agosto 2012): 83–86. http://dx.doi.org/10.1017/s1743921312021163.
Testo completoAbstract (sommario):
AbstractA common approach to determining distances to stars without astrometric information is to compare stellar evolution models with parameters obtained from spectroscopic techniques. This method is routinely applied in the context of large-scale stellar surveys out to distances of several kpc. However, systematic errors may arise because of inaccurate spectroscopic parameters. We explore the effects of non-local thermodynamic equilibrium (NLTE) on the determination of surface gravities and metallicities for a large sample of metal-poor stars within approximately 10 kpc of the Sun. Using the improved Teff scale, we then show that stellar parameters estimated based on the widely used method of 1D LTE excitation-ionization balance of Fe results in distances which are systematically in error. For metal-poor giants, [Fe/H] ~ −2 dex, the distances can be overestimated by up to 70%. We compare the results with those from the Radial Velocity Experiment Survey catalogue (rave) for the stars in common, and find similar offsets.
36
Shao, Zhengwei, e Andreas Burkhalter. "Role of GABAB Receptor-Mediated Inhibition in Reciprocal Interareal Pathways of Rat Visual Cortex". Journal of Neurophysiology 81, n. 3 (1 marzo 1999): 1014–24. http://dx.doi.org/10.1152/jn.1999.81.3.1014.
Testo completoAbstract (sommario):
Role of GABAB receptor-mediated inhibition in reciprocal interareal pathways of rat visual cortex. In neocortex, synaptic inhibition is mediated by γ-aminobutyric acid-A (GABAA) and GABAB receptors. By using intracellular and patch-clamp recordings in slices of rat visual cortex we studied the balance of excitation and inhibition in different intracortical pathways. The study was focused on the strength of fast GABAA- and slow GABAB-mediated inhibition in interareal forward and feedback connections between area 17 and the secondary, latero-medial visual area (LM). Our results demonstrate that in most layer 2/3 neurons forward inputs elicited excitatory postsynaptic potentials (EPSPs) that were followed by fast GABAA- and slow GABAB-mediated hyperpolarizing inhibitory postsynaptic potentials (IPSPs). These responses resembled those elicited by horizontal connections within area 17 and those evoked by stimulation of the layer 6/white matter border. In contrast, in the feedback pathway hyperpolarizing fast and slow IPSPs were rare. However weak fast and slow IPSPs were unmasked by bath application of GABAB receptor antagonists. Because in the feedback pathway disynaptic fast and slow IPSPs were rare, polysynaptic EPSPs were more frequent than in forward, horizontal, and interlaminar circuits and were activated over a broader stimulus range. In addition, in the feedback pathway large-amplitude polysynaptic EPSPs were longer lasting and showed a late component whose onset coincided with that of slow IPSPs. In the forward pathway these late EPSPs were only seen with stimulus intensities that were below the activation threshold of slow IPSPs. Unlike strong forward inputs, feedback stimuli of a wide range of intensities increased the rate of ongoing neuronal firing. Thus, when forward and feedback inputs are simultaneously active, feedback inputs may provide late polysynaptic excitation that can offset slow IPSPs evoked by forward inputs and in turn may promote recurrent excitation through local intracolumnar circuits. This may provide a mechanism by which feedback inputs from higher cortical areas can amplify afferent signals in lower areas.
37
Pietra, Gianluca, Tiziana Bonifacino, Davide Talamonti, Giambattista Bonanno, Alessandro Sale, Lucia Galli e Laura Baroncelli. "Visual Cortex Engagement in Retinitis Pigmentosa". International Journal of Molecular Sciences 22, n. 17 (30 agosto 2021): 9412. http://dx.doi.org/10.3390/ijms22179412.
Testo completoAbstract (sommario):
Retinitis pigmentosa (RP) is a family of inherited disorders caused by the progressive degeneration of retinal photoreceptors. There is no cure for RP, but recent research advances have provided promising results from many clinical trials. All these therapeutic strategies are focused on preserving existing photoreceptors or substituting light-responsive elements. Vision recovery, however, strongly relies on the anatomical and functional integrity of the visual system beyond photoreceptors. Although the retinal structure and optic pathway are substantially preserved at least in early stages of RP, studies describing the visual cortex status are missing. Using a well-established mouse model of RP, we analyzed the response of visual cortical circuits to the progressive degeneration of photoreceptors. We demonstrated that the visual cortex goes through a transient and previously undescribed alteration in the local excitation/inhibition balance, with a net shift towards increased intracortical inhibition leading to improved filtering and decoding of corrupted visual inputs. These results suggest a compensatory action of the visual cortex that increases the range of residual visual sensitivity in RP.
38
Amarsi, A. M., S. Liljegren e P. E. Nissen. "3D non-LTE iron abundances in FG-type dwarfs". Astronomy & Astrophysics 668 (dicembre 2022): A68. http://dx.doi.org/10.1051/0004-6361/202244542.
Testo completoAbstract (sommario):
Iron is one of the most important elements in-stellar astrophysics. However, spectroscopic measurements of its abundance are prone to systematic modelling errors. We present three dimensional non-local thermodynamic equilibrium (3D non-LTE) calculations across 32 STAGGER-grid models with effective temperatures from 5000 K to 6500 K, surface gravities of 4.0 dex and 4.5 dex, and metallicities from −3 dex to 0 dex, and we study the effects on 171 Fe i and 12 Fe ii optical lines. In warm metal-poor stars, the 3D non-LTE abundances are up to 0.5 dex larger than 1D LTE abundances inferred from Fe i lines of an intermediate excitation potential. In contrast, the 3D non-LTE abundances can be 0.2 dex smaller in cool metal-poor stars when using Fe i lines of a low excitation potential. The corresponding abundance differences between 3D non-LTE and 1D non-LTE are generally less severe but can still reach ±0.2 dex. For Fe ii lines, the 3D abundances range from up to 0.15 dex larger to 0.10 dex smaller than 1D abundances, with negligible departures from 3D LTE except for the warmest stars at the lowest metallicities. The results were used to correct 1D LTE abundances of the Sun and Procyon (HD 61421), and of the metal-poor stars HD 84937 and HD 140283, using an interpolation routine based on neural networks. The 3D non-LTE models achieve an improved ionisation balance in all four stars. In the two metal-poor stars, they removed excitation imbalances amounting to 250 K to 300 K errors in effective temperature. For Procyon, the 3D non-LTE models suggest [Fe/H] = 0.11 ± 0.03, which is significantly larger than literature values based on simpler models. We make the 3D non-LTE interpolation routine for FG-type dwarfs publicly available, in addition to 1D non-LTE departure coefficients for standard MARCS models of FGKM-type dwarfs and giants. These tools, together with an extended 3D LTE grid for Fe ii from 2019, can help improve the accuracy of stellar parameter and iron abundance determinations for late-type stars.
39
Calvagna, Chiara, Andrea Azelio Mencaglia, Iacopo Osticioli, Daniele Ciofini e Salvatore Siano. "Novel Probe for Thermally Controlled Raman Spectroscopy Using Online IR Sensing and Emissivity Measurements". Sensors 22, n. 7 (31 marzo 2022): 2680. http://dx.doi.org/10.3390/s22072680.
Testo completoAbstract (sommario):
Temperature rise during Raman spectroscopy can induce chemical alterations of the material under analysis and seriously affect its characterization. Thus, such photothermal side effects can represent a serious problem to be carefully controlled in order to safeguard the integrity of the material and its spectral features. In this work, an innovative probe for thermally controlled portable Raman spectroscopy (exc. 785 nm) equipped with infrared sensing lines was developed. It included an infrared source and two thermopile sensors, which allowed to perform real-time measurements of the local emissivity of the material surface under laser excitation. The emissivity, which is needed in order to monitor the temperature of the irradiated surface through infrared radiation measurements, represents the complementary component of the reflectance in the radiative energy balance. Thus, total reflectance, temperature measurements and Raman spectroscopy were integrated in the present probe. After independently assessing the reliability of the former in order to derive the emissivity of variety of materials, the probe was successfully applied on pigments, paint layers, and a painting on canvas. The results achieved evidence the significant exploitation potential of the novel tool.
40
Potnis, V. V., Ketan G. Albhar, Pritamsinh Arjun Nanaware e Vishal S. Pote. "A Review on Epilepsy and its Management". Journal of Drug Delivery and Therapeutics 10, n. 3 (15 maggio 2020): 273–79. http://dx.doi.org/10.22270/jddt.v10i3.4090.
Testo completoAbstract (sommario):
Today, people face various types of stress in everyday fast life and most people in the world suffer from various neurological disorder. Epilepsy is one of the most common neurological disorders of the brain, affecting about 50 million people around the world, and 90% of them are coming from developing countries. Genetic factors and brain infection, stroke, tumors and epilepsy cause high fever. It imposes a great economic burden on the health systems of countries associated with stigma and discrimination against the patient and also his family in the community, in the workplace, school and home. Many patients with epilepsy suffer from severe emotional stress, behavioral disorders and extreme social isolation. There are many different types of seizure and mechanisms by which the brain generates seizures. The two features of generating seizures are hyperexcitability of neurons and a hyper synchronousneural circuits. A variety of mechanisms alters the balance between excitation and inhibition in predisposing brain local or generalized hyperexcitability region and a hypersynchronia. Purpose of the review is to discuss the history, epidemiology, etiology, pathophysiology, classification of epilepsy, symtomps, diagnosis, management of epilepsy and future trends.
Keywords: Anti-epileptic drugs, pathophysiology, seizures, epidemiology, hypersynchrony
41
Bharadwaj, Hari, e Varsha Mysore Athreya. "Effects of age-related cochlear deafferentation and central gain on auditory scene analysis". Journal of the Acoustical Society of America 154, n. 4_supplement (1 ottobre 2023): A333. http://dx.doi.org/10.1121/10.0023710.
Testo completoAbstract (sommario):
Animal models show that cochlear afferent nerve endings are more vulnerable than sensory hair cells to age-related damage. Because such cochlear deafferentation is not apparent in standard audiometry, the extent to which it contributes to deficits in human hearing is debated, and the intervening neural processes are poorly characterized. This presentation will describe our efforts to address these gaps through co-ordinated experiments in at-risk humans and a chinchilla model. Our results suggest that cochlear deafferentation is widespread in middle age despite clinically normal audiometric sensitivity. Furthermore, the resulting reduction in peripheral input appears to trigger compensatory central “gain” at the cortical level, likely through altered local balance of excitation and inhibition. Consistent with the important role of inhibition in parsing temporal regularities across different frequency components of sound, central gain is also associated with reduced ability to perceptually segregate acoustic scenes with multiple sources into individual perceptual streams. Taken together, our results suggest that age-related cochlear deafferentation may affect hearing not only by reducing the fidelity of input encoding but also by interfering with the central auditory system’s ability to extract targets in noisy environments.
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Armillotta, Lucia, Eve C. Ostriker e Yan-Fei Jiang. "Cosmic-Ray Transport in Varying Galactic Environments". Astrophysical Journal 929, n. 2 (1 aprile 2022): 170. http://dx.doi.org/10.3847/1538-4357/ac5fa9.
Testo completoAbstract (sommario):
Abstract We study the propagation of mildly relativistic cosmic rays (CRs) in multiphase interstellar medium environments with conditions typical of nearby disk galaxies. We employ the techniques developed in Armillotta et al. to postprocess three high-resolution TIGRESS magnetohydrodynamic simulations modeling local patches of star-forming galactic disks. Together, the three simulations cover a wide range of gas surface density, gravitational potential, and star formation rate (SFR). Our prescription for CR propagation includes the effects of advection by the background gas, streaming along the magnetic field at the local ion Alfvén speed, and diffusion relative to the Alfvén waves, with the diffusion coefficient set by the balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We find that the combined transport processes are more effective in environments with higher SFR. These environments are characterized by higher-velocity hot outflows (created by clustered supernovae) that rapidly advect CRs away from the galactic plane. As a consequence, the ratio of midplane CR pressure to midplane gas pressures decreases with increasing SFR. We also use the postprocessed simulations to make predictions regarding the potential dynamical impacts of CRs. The relatively flat CR pressure profiles near the midplane argue that they would not provide significant support against gravity for most of the ISM mass. However, the CR pressure gradients are larger than the other pressure gradients in the extraplanar region (∣z∣ > 0.5 kpc), suggesting that CRs may affect the dynamics of galactic fountains and/or winds. The degree of this impact is expected to increase in environments with lower SFR.
43
Armillotta, Lucia, Eve C. Ostriker e Yan-Fei Jiang. "Cosmic-Ray Transport in Varying Galactic Environments". Astrophysical Journal 929, n. 2 (1 aprile 2022): 170. http://dx.doi.org/10.3847/1538-4357/ac5fa9.
Testo completoAbstract (sommario):
Abstract We study the propagation of mildly relativistic cosmic rays (CRs) in multiphase interstellar medium environments with conditions typical of nearby disk galaxies. We employ the techniques developed in Armillotta et al. to postprocess three high-resolution TIGRESS magnetohydrodynamic simulations modeling local patches of star-forming galactic disks. Together, the three simulations cover a wide range of gas surface density, gravitational potential, and star formation rate (SFR). Our prescription for CR propagation includes the effects of advection by the background gas, streaming along the magnetic field at the local ion Alfvén speed, and diffusion relative to the Alfvén waves, with the diffusion coefficient set by the balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We find that the combined transport processes are more effective in environments with higher SFR. These environments are characterized by higher-velocity hot outflows (created by clustered supernovae) that rapidly advect CRs away from the galactic plane. As a consequence, the ratio of midplane CR pressure to midplane gas pressures decreases with increasing SFR. We also use the postprocessed simulations to make predictions regarding the potential dynamical impacts of CRs. The relatively flat CR pressure profiles near the midplane argue that they would not provide significant support against gravity for most of the ISM mass. However, the CR pressure gradients are larger than the other pressure gradients in the extraplanar region (∣z∣ > 0.5 kpc), suggesting that CRs may affect the dynamics of galactic fountains and/or winds. The degree of this impact is expected to increase in environments with lower SFR.
44
Farnan, Julia, Joshua Jackson e Edward Hartsough. "FSMP-03. INVESTIGATING CO-OPTED ASTROCYTIC METABOLISM IN MELANOMA BRAIN METASTASIS". Neuro-Oncology Advances 3, Supplement_1 (1 marzo 2021): i16—i17. http://dx.doi.org/10.1093/noajnl/vdab024.068.
Testo completoAbstract (sommario):
Abstract Melanoma, an aggressive form of skin cancer, frequently metastasizes to the brain. While peripheral melanoma is largely treatable, MBM fail to respond to current therapeutics and is a clear unmet clinical need. Initial clinical symptoms of Melanoma Brain Metastases (MBM) typically include headaches, seizures and other neurological deficits, suggesting that MBM disrupt normal brain functions. One of the major cell types that melanoma encounter and interact with during brain metastasis are astrocytes. Astrocytes, the most abundant cell in the brain, interact with neurons and the vasculature, provide trophic and energetic support to neurons, and regulate local blood flow. Metabolic pathways in astrocytes, particularly the glutamate-glutamine cycle, are essential for the recycling and resupply of neurotransmitters needed to maintain the excitation/inhibition balance. We propose that MBM co-opt astrocytic metabolism, fueling MBM growth, and deplete metabolic intermediates crucial for neuronal activity leading to altered neurologic function. We begin to unravel the metabolic interactions between astrocytes and MBM using novel modeling platforms with genetic and pharmacological tools to manipulate the tumor microenvironment. This project investigates the contribution of astrocytic metabolism to MBM growth. We intend on dissecting the distinct metabolic needs of metastatic brain melanoma in the CNS microenvironment and the subsequent neurological consequences. Completion of this project will provide a platform to study MBM and interaction with the local brain microenvironment. Inhibiting metabolic interactions between melanoma and glial cells may provide new avenue for therapeutic targeting of MBM.
45
Liang, Junhao, e Changsong Zhou. "Criticality enhances the multilevel reliability of stimulus responses in cortical neural networks". PLOS Computational Biology 18, n. 1 (31 gennaio 2022): e1009848. http://dx.doi.org/10.1371/journal.pcbi.1009848.
Testo completoAbstract (sommario):
Cortical neural networks exhibit high internal variability in spontaneous dynamic activities and they can robustly and reliably respond to external stimuli with multilevel features–from microscopic irregular spiking of neurons to macroscopic oscillatory local field potential. A comprehensive study integrating these multilevel features in spontaneous and stimulus–evoked dynamics with seemingly distinct mechanisms is still lacking. Here, we study the stimulus–response dynamics of biologically plausible excitation–inhibition (E–I) balanced networks. We confirm that networks around critical synchronous transition states can maintain strong internal variability but are sensitive to external stimuli. In this dynamical region, applying a stimulus to the network can reduce the trial-to-trial variability and shift the network oscillatory frequency while preserving the dynamical criticality. These multilevel features widely observed in different experiments cannot simultaneously occur in non-critical dynamical states. Furthermore, the dynamical mechanisms underlying these multilevel features are revealed using a semi-analytical mean-field theory that derives the macroscopic network field equations from the microscopic neuronal networks, enabling the analysis by nonlinear dynamics theory and linear noise approximation. The generic dynamical principle revealed here contributes to a more integrative understanding of neural systems and brain functions and incorporates multimodal and multilevel experimental observations. The E–I balanced neural network in combination with the effective mean-field theory can serve as a mechanistic modeling framework to study the multilevel neural dynamics underlying neural information and cognitive processes.
46
Kühn, Marco J., Lorenzo Talà, Yuki F. Inclan, Ramiro Patino, Xavier Pierrat, Iscia Vos, Zainebe Al-Mayyah et al. "Mechanotaxis directs Pseudomonas aeruginosa twitching motility". Proceedings of the National Academy of Sciences 118, n. 30 (22 luglio 2021): e2101759118. http://dx.doi.org/10.1073/pnas.2101759118.
Testo completoAbstract (sommario):
The opportunistic pathogen Pseudomonas aeruginosa explores surfaces using twitching motility powered by retractile extracellular filaments called type IV pili (T4P). Single cells twitch by sequential T4P extension, attachment, and retraction. How single cells coordinate T4P to efficiently navigate surfaces remains unclear. We demonstrate that P. aeruginosa actively directs twitching in the direction of mechanical input from T4P in a process called mechanotaxis. The Chp chemotaxis-like system controls the balance of forward and reverse twitching migration of single cells in response to the mechanical signal. Collisions between twitching cells stimulate reversals, but Chp mutants either always or never reverse. As a result, while wild-type cells colonize surfaces uniformly, collision-blind Chp mutants jam, demonstrating a function for mechanosensing in regulating group behavior. On surfaces, Chp senses T4P attachment at one pole, thereby sensing a spatially resolved signal. As a result, the Chp response regulators PilG and PilH control the polarization of the extension motor PilB. PilG stimulates polarization favoring forward migration, while PilH inhibits polarization, inducing reversal. Subcellular segregation of PilG and PilH efficiently orchestrates their antagonistic functions, ultimately enabling rapid reversals upon perturbations. The distinct localization of response regulators establishes a signaling landscape known as local excitation–global inhibition in higher-order organisms, identifying a conserved strategy to transduce spatially resolved signals.
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Sanchez-Vives, Maria V., Maurizio Mattia, Albert Compte, Maria Perez-Zabalza, Milena Winograd, Vanessa F. Descalzo e Ramon Reig. "Inhibitory Modulation of Cortical Up States". Journal of Neurophysiology 104, n. 3 (settembre 2010): 1314–24. http://dx.doi.org/10.1152/jn.00178.2010.
Testo completoAbstract (sommario):
The balance between excitation and inhibition is critical in the physiology of the cerebral cortex. To understand the influence of inhibitory control on the emergent activity of the cortical network, inhibition was progressively blocked in a slice preparation that generates spontaneous rhythmic up states at a similar frequency to those occurring in vivo during slow-wave sleep or anesthesia. Progressive removal of inhibition induced a parametric shortening of up state duration and elongation of the down states, the frequency of oscillations decaying. Concurrently, a gradual increase in the network firing rate during up states occurred. The slope of transitions between up and down states was quantified for different levels of inhibition. The slope of upward transitions reflects the recruitment of the local network and was progressively increased when inhibition was decreased, whereas the speed of activity propagation became faster. Removal of inhibition eventually resulted in epileptiform activity. Whereas gradual reduction of inhibition induced linear changes in up/down states and their propagation, epileptiform activity was the result of a nonlinear transformation. A computational network model showed that strong recurrence plus activity-dependent hyperpolarizing currents were sufficient to account for the observed up state modulations and predicted an increase in activity-dependent hyperpolarization following up states when inhibition was decreased, which was confirmed experimentally.
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Zurbrügg, R., S. Suter, M. F. Lehmann, B. Wehrli e D. B. Senn. "Organic carbon and nitrogen export from a tropical dam-impacted floodplain system". Biogeosciences 10, n. 1 (4 gennaio 2013): 23–38. http://dx.doi.org/10.5194/bg-10-23-2013.
Testo completoAbstract (sommario):
Abstract. Tropical floodplains play an important role in organic matter transport, storage, and transformation between headwaters and oceans. However, the fluxes and quality of organic carbon (OC) and organic nitrogen (ON) in tropical river-floodplain systems are not well constrained. We explored the quantity and characteristics of dissolved and particulate organic matter (DOM and POM, respectively) in the Kafue River flowing through the Kafue Flats (Zambia), a tropical river-floodplain system in the Zambezi River basin. During the flooding season, > 80% of the Kafue River water passed through the floodplain, mobilizing large quantities of OC and ON, which resulted in a net export of 69–119 kg OC km−2 d−1 and 3.8–4.7 kg ON km−2 d−1, 80% of which was in the dissolved form. The elemental C : N ratio of ~ 20, the comparatively high δ13C values of −25‰ to −21‰, and its spectroscopic properties (excitation-emission matrices) showed that DOM in the river was mainly of terrestrial origin. Despite a threefold increase in OC loads due to inputs from the floodplain, the characteristics of the riverine DOM remained relatively constant along the sampled 410-km river reach. This suggests that floodplain DOM displayed properties similar to those of DOM leaving the upstream reservoir and implied that the DOM produced in the reservoir was relatively short-lived. In contrast, the particulate fraction was 13C-depleted (−29‰) and had a C : N ratio of ~ 8, which indicated that POM originated from phytoplankton production in the reservoir and in the floodplain, rather than from plant debris or resuspended sediments. While the upstream dam had little effect on the DOM pool, terrestrial particles were retained, and POM from algal and microbial sources was released to the river. A nitrogen mass balance over the 2200 km2 flooded area revealed an annual deficit of 15 500–22 100 t N in the Kafue Flats. The N isotope budget suggests that these N losses are balanced by intense N-fixation. Our study shows that the Kafue Flats are a significant local source of OC and ON to downstream ecosystems and illustrates how the composition of riverine OM can be altered by dams and floodplains in tropical catchments.
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Shirani, Farshad, e Hannah Choi. "On the physiological and structural contributors to the overall balance of excitation and inhibition in local cortical networks". Journal of Computational Neuroscience, 14 ottobre 2023. http://dx.doi.org/10.1007/s10827-023-00863-x.
Testo completoAbstract (sommario):
AbstractOverall balance of excitation and inhibition in cortical networks is central to their functionality and normal operation. Such orchestrated co-evolution of excitation and inhibition is established through convoluted local interactions between neurons, which are organized by specific network connectivity structures and are dynamically controlled by modulating synaptic activities. Therefore, identifying how such structural and physiological factors contribute to establishment of overall balance of excitation and inhibition is crucial in understanding the homeostatic plasticity mechanisms that regulate the balance. We use biologically plausible mathematical models to extensively study the effects of multiple key factors on overall balance of a network. We characterize a network’s baseline balanced state by certain functional properties, and demonstrate how variations in physiological and structural parameters of the network deviate this balance and, in particular, result in transitions in spontaneous activity of the network to high-amplitude slow oscillatory regimes. We show that deviations from the reference balanced state can be continuously quantified by measuring the ratio of mean excitatory to mean inhibitory synaptic conductances in the network. Our results suggest that the commonly observed ratio of the number of inhibitory to the number of excitatory neurons in local cortical networks is almost optimal for their stability and excitability. Moreover, the values of inhibitory synaptic decay time constants and density of inhibitory-to-inhibitory network connectivity are critical to overall balance and stability of cortical networks. However, network stability in our results is sufficiently robust against modulations of synaptic quantal conductances, as required by their role in learning and memory. Our study based on extensive bifurcation analyses thus reveal the functional optimality and criticality of structural and physiological parameters in establishing the baseline operating state of local cortical networks.
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Liang, Junhao, Zhuda Yang e Changsong Zhou. "Excitation–Inhibition Balance, Neural Criticality, and Activities in Neuronal Circuits". Neuroscientist, 31 gennaio 2024. http://dx.doi.org/10.1177/10738584231221766.
Testo completoAbstract (sommario):
Neural activities in local circuits exhibit complex and multilevel dynamic features. Individual neurons spike irregularly, which is believed to originate from receiving balanced amounts of excitatory and inhibitory inputs, known as the excitation–inhibition balance. The spatial-temporal cascades of clustered neuronal spikes occur in variable sizes and durations, manifested as neural avalanches with scale-free features. These may be explained by the neural criticality hypothesis, which posits that neural systems operate around the transition between distinct dynamic states. Here, we summarize the experimental evidence for and the underlying theory of excitation–inhibition balance and neural criticality. Furthermore, we review recent studies of excitatory–inhibitory networks with synaptic kinetics as a simple solution to reconcile these two apparently distinct theories in a single circuit model. This provides a more unified understanding of multilevel neural activities in local circuits, from spontaneous to stimulus-response dynamics.