1,721,068 research outputs found
Stochastic synaptic plasticity in deterministic aVLSI networks of spiking neurons
Full text linkChicca E, Fusi S. Stochastic synaptic plasticity in deterministic aVLSI networks of spiking neurons. In: Rattay F, ed. Proceedings of the World Congress on Neuroinformatics. Vienna: ARGESIM/ASIM Verlag; 2001: 468-477.Stochastic learning solves the stability-plasticity problem (Fusi et al., 2000a)
but raises new issues related to the generation of the proper noise driving
the synaptic dynamics. Here we show that a simple, fully deterministic,
spike-driven synaptic device can make use of the network generated vari-
ability in the neuronal activity to drive the required stochastic mechanism.
Randomness emerges naturally from the interaction of deterministic neu-
rons, and no extra source of noise is needed. Learning and forgetting
rates of the network can be easily controlled by changing the statistics of
the spike trains without changing any inherent parameter of the synaptic
dynamics
Synthesis and Characterization of 3-Hydroxy-2-(5'-Hydroxypentyl)-4H-Pyran-4-one and Study of Its Complexation with Iron(III)
No full textAbstract: With the special focus to obtain a new tridentate ligand able to coordinate Fe(III), 3-hydroxy-2-(5'-hydroxypentyl)-4H-pyran-4-one (5-H) has been synthesized. Iron/ligand solution chemistry has been investigated in aqueous solution by ESI-MS and cyclic voltammetric measurements. The physiologic predominant specie is the tris-chelate complex as Job test attested. The electrode potential of the [FeIII(5)3]/[FeII(5)3]– couple was evaluated to be –0.54 V vs. SCE, pH 7.4
The response of cortical neurons to in vivo-like input current: theory and experiment: I. Noisy inputs with stationary statistics.
Full text linkThe study of several aspects of the collective dynamics of interacting neurons can be highly simplified if one assumes that the statistics of the synaptic input is the same for a large population of similarly behaving neurons (mean field approach). In particular, under such an assumption, it is possible to determine and study all the equilibrium points of the network dynamics when the neuronal response to noisy, in vivo-like, synaptic currents is known. The response function can be computed analytically for simple integrate-and-fire neuron models and it can be measured directly in experiments in vitro. Here we review theoretical and experimental results about the neural response to noisy inputs with stationary statistics. These response functions are important to characterize the collective neural dynamics that are proposed to be the neural substrate of working memory, decision making and other cognitive functions. Applications to the case of time-varying inputs are reviewed in a companion paper (Giugliano et al. in Biol Cybern, 2008). We conclude that modified integrate-and-fire neuron models are good enough to reproduce faithfully many of the relevant dynamical aspects of the neuronal response measured in experiments on real neurons in vitro
Photocycloadditions on 2-Methyloxazolo[5,4-b]pyridine
No full textThe title compound undergoes photocycloadditions with both electron-poor alkenes (methacrylonitrile) and electron-rich alkenes (ethyl vinyl ether and furan). The initial photoadducts evolve into a variety of compounds. In the photoreaction with methacrylonitrile, oxazoloazocines 5 and 7 and cyclopentenylidenes 6Z and 6E are obtained; the photoadducts with vinyl ether yield oxazoloazocines 9 and 11, substituted oxazoles 10 and 12, and pyrrolopyridine 13; from the reaction with furan the furylpyridine 14 was isolated. ((C) Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2002)
5-Amino-8-(1-aminoethylidene)-8H-tetrazolo[1,5-a]pyridin-7-one dihydrate
No full textThe title compound, C7H8N6O·2H 2O, contains a tetrazole ring fused to a substituted pyridone ring. Bond lengths correspond to delocalized π electrons in the tetrazole moiety and a push-pull effect in the pyridone ring. An extended network of hydrogen bonds connects the molecules in planes parallel to the be plane, while the water molecules form chains parallel to the a axis. © 2003 International Union of Crystallography Printed in Great Britain - all rights reserved
Photochemistry of 4,6-Diazido-3-methylisoxazolo[4,5-c]pyridines: a convenient entry to 3-Methylisoxazolo[1,3]diazepine system
No full textUV irradiation of 4,6-diazido-3-methylisoxazolo[4,5-c] pyridine in methanol gives the 3-methylisoxazolo-1,3-diazepine derivatives 3,4 by nitrogen loss and solvent addition
Event-driven simulation of spiking neurons with stochastic dynamics
Full text linkWe present a new technique, based on a proposed event-based strategy (Mattia & Del Giudice, 2000), for efficiently simulating large networks of simple model neurons. The strategy was based on the fact that interactions among neurons occur by means of events that are well localized in time (the action potentials) and relatively rare. In the interval between two of these events, the state variables associated with a model neuron or a synapse evolved deterministically and in a predictable way. Here, we extend the event-driven simulation strategy to the case in which the dynamics of the state variables in the inter-event intervals are stochastic. This extension captures both the situation in which the simulated neurons are inherently noisy and the case in which they are embedded in a very large network and receive a huge number of random synaptic inputs. We show how to effectively include the impact of large background populations into neuronal dynamics by means of the numerical evaluation of the statistical properties of single-model neurons under random current injection. The new simulation strategy allows the study of networks of interacting neurons with an arbitrary number of external afferents and inherent stochastic dynamics
MAXIMAL OXYGEN CONSUMPTION AND ENERGY COST OF RUNNING AFTER A LONG-LASTING RACE: THE 100 KM OF SAHARA
No full textDiastereoselective synthesis of beta-aminocyclopentene sulfonic acid via hetero Diels-Alder reaction
No full textA new cyclopentene GABA analogue was synthesized as a conformationally rigid analogue of the epilepsy drug vigabatrin. N-Sulfinyl dienophile Diels-Alder methodology, followed by alkaline hydrolysis of the corresponding dihydrothiazine oxide, oxidation and deprotection of the amino group gave cis-4-aminocyclopent-2-ene-1-sulfonic acid. The corresponding N,N-dimethylsulfinamide was also obtained. © 2006 Elsevier Ltd. All rights reserved
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