3,656 research outputs found
Renewal theory of coupled neuronal pools
A theory is provided to analyze the dynamics of delay-coupled pools of spiking neurons based on stability
analysis of stationary firing. Transitions between stable and unstable regimes can be predicted by bifurcation analysis of the underlying integral dynamics. Close to the bifurcation point the network exhibits slowly changingactivities and allows for slow collective phenomena like continuous attractors
GABA-enhanced collective behavior in neuronal axons underlies persistent gamma-frequency oscillations
Gamma (30–80 Hz) oscillations occur in mammalian electroencephalogram in a manner that indicates cognitive relevance. In vitro models of gamma oscillations demonstrate two forms of oscillation: one occurring transiently and driven by discrete afferent input and the second occurring persistently in response to activation of excitatory metabotropic receptors. The mechanism underlying persistent gamma oscillations has been suggested to involve gap-junctional communication between axons of principal neurons, but the precise relationship between this neuronal activity and the gamma oscillation has remained elusive. Here we demonstrate that gamma oscillations coexist with high-frequency oscillations (>90 Hz). High-frequency oscillations can be generated in the axonal plexus even when it is physically isolated from pyramidal cell bodies. They were enhanced in networks by nonsomatic -aminobutyric acid type A (GABAA) receptor activation, were modulated by perisomatic GABAA receptor-mediated synaptic input to principal cells, and provided the phasic input to interneurons required to generate persistent gamma-frequency oscillations. The data suggest that high-frequency oscillations occurred as a consequence of random activity within the axonal plexus. Interneurons provide a mechanism by which this random activity is both amplified and organized into a coherent network rhythm
Dynamically-Coupled Oscillators -- Cooperative Behavior via Dynamical Interaction --
We propose a theoretical framework to study the cooperative behavior of
dynamically coupled oscillators (DCOs) that possess dynamical interactions.
Then, to understand synchronization phenomena in networks of interneurons which
possess inhibitory interactions, we propose a DCO model with dynamics of
interactions that tend to cause 180-degree phase lags. Employing an approach
developed here, we demonstrate that although our model displays synchronization
at high frequencies, it does not exhibit synchronization at low frequencies
because this dynamical interaction does not cause a phase lag sufficiently
large to cancel the effect of the inhibition. We interpret the disappearance of
synchronization in our model with decreasing frequency as describing the
breakdown of synchronization in the interneuron network of the CA1 area below
the critical frequency of 20 Hz.Comment: 10 pages, 3 figure
Bacterial microbiota composition of a common ectoparasite of cavity‐breeding birds, the Hen Flea Ceratophyllus gallinae
Experimental field studies have demonstrated negative fitness consequences of Hen Flea Ceratophyllus gallinae infestations for bird hosts, yet it is currently unclear whether these negative effects are a direct consequence of flea-induced blood loss or a result of flea-borne pathogen transmission. Here we used a 16S rRNA gene sequencing approach to characterize the bacterial microbiota community of Hen Fleas collected from Great Tit Parus major nests and found that Brevibacterium (Actinobacteria), Staphylococcus (Firmicutes), Stenotrophomonas (Proteobacteria), Massilia (Proteobacteria), as well as the arthropod endosymbionts 'Candidatus Lariskella' and 'Candidatus Midichloria' were most abundant. We found evidence for the occurrence of Staphylococcus spp. in Hen Fleas, which may cause opportunistic infections in bird hosts, but not of other known pathogens commonly transmitted by other flea species, such as Bartonella spp. or Rickettsia spp. However, Hen Fleas might transmit other pathogens (e.g. viruses or bacteria that are not currently recognized as bird pathogens), which may contribute to the negative fitness consequences of Hen Flea infestations in addition to direct blood loss or secondary infections of wounds caused by biting fleas.Peer reviewe
Conditional sampling for barrier option pricing under the LT method
We develop a conditional sampling scheme for pricing knock-out barrier
options under the Linear Transformations (LT) algorithm from Imai and Tan
(2006). We compare our new method to an existing conditional Monte Carlo scheme
from Glasserman and Staum (2001), and show that a substantial variance
reduction is achieved. We extend the method to allow pricing knock-in barrier
options and introduce a root-finding method to obtain a further variance
reduction. The effectiveness of the new method is supported by numerical
results
P02.165. A comparative effectiveness trial of high-quality vitamin D3 nutritional supplements to replete serum vitamin D
Astrometric jitter of the sun as a star
The daily variation of the solar photocenter over some 11 years is derived
from the Mount Wilson data reprocessed by Ulrich et al. 2010 to closely match
the surface distribution of solar irradiance. The standard deviations of
astrometric jitter are 0.52 AU and 0.39 AU in the equatorial and the
axial dimensions, respectively. The overall dispersion is strongly correlated
with the solar cycle, reaching AU at the maximum activity in 2000.
The largest short-term deviations from the running average (up to 2.6 AU)
occur when a group of large spots happen to lie on one side with respect to the
center of the disk. The amplitude spectrum of the photocenter variations never
exceeds 0.033 AU for the range of periods 0.6--1.4 yr, corresponding to
the orbital periods of planets in the habitable zone. Astrometric detection of
Earth-like planets around stars as quiet as the Sun is not affected by star
spot noise, but the prospects for more active stars may be limited to giant
planets.Comment: Accepted in Ap
Genetically altered AMPA-type glutamate receptor kinetics in interneurons disrupt long-range synchrony of gamma oscillation
Gamma oscillations synchronized between distant neuronal populations may be critical for binding together brain regions devoted to common processing tasks. Network modeling predicts that such synchrony depends in part on the fast time course of excitatory postsynaptic potentials (EPSPs) in interneurons, and that even moderate slowing of this time course will disrupt synchrony. We generated mice with slowed interneuron EPSPs by gene targeting, in which the gene encoding the 67-kDa form of glutamic acid decarboxylase (GAD67) was altered to drive expression of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subunit GluR-B. GluR-B is a determinant of the relatively slow EPSPs in excitatory neurons and is normally expressed at low levels in γ-aminobutyric acid (GABA)ergic interneurons, but at high levels in the GAD-GluR-B mice. In both wild-type and GAD-GluR-B mice, tetanic stimuli evoked gamma oscillations that were indistinguishable in local field potential recordings. Remarkably, however, oscillation synchrony between spatially separated sites was severely disrupted in the mutant, in association with changes in interneuron firing patterns. The congruence between mouse and model suggests that the rapid time course of AMPA receptor-mediated EPSPs in interneurons might serve to allow gamma oscillations to synchronize over distance
A role for fast rhythmic bursting neurons in cortical gamma oscillations in vitro
Basic cellular and network mechanisms underlying gamma frequency oscillations (30–80 Hz) have been well characterized in the hippocampus and associated structures. In these regions, gamma rhythms are seen as an emergent property of networks of principal cells and fast-spiking interneurons. In contrast, in the neocortex a number of elegant studies have shown that specific types of principal neuron exist that are capable of generating powerful gamma frequency outputs on the basis of their intrinsic conductances alone. These fast rhythmic bursting (FRB) neurons (sometimes referred to as "chattering" cells) are activated by sensory stimuli and generate multiple action potentials per gamma period. Here, we demonstrate that FRB neurons may function by providing a large-scale input to an axon plexus consisting of gap-junctionally connected axons from both FRB neurons and their anatomically similar counterparts regular spiking neurons. The resulting network gamma oscillation shares all of the properties of gamma oscillations generated in the hippocampus but with the additional critical dependence on multiple spiking in FRB cells
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