2,391 research outputs found
Double coherence resonance in neuron models driven by discrete correlated noise
We study the influence of correlations among discrete stochastic excitatory
or inhibitory inputs on the response of the FitzHugh-Nagumo neuron model. For
any level of correlation the emitted signal exhibits at some finite noise
intensity a maximal degree of regularity, i.e., a coherence resonance.
Furthermore, for either inhibitory or excitatory correlated stimuli a {\it
Double Coherence Resonance} (DCR) is observable. DCR refers to a (absolute)
maximum coherence in the output occurring for an optimal combination of noise
variance and correlation. All these effects can be explained by taking
advantage of the discrete nature of the correlated inputs.Comment: 4 pages, 3 figures in eps, to appear in Physical Review Letter
Auto and crosscorrelograms for the spike response of LIF neurons with slow synapses
An analytical description of the response properties of simple but realistic
neuron models in the presence of noise is still lacking. We determine
completely up to the second order the firing statistics of a single and a pair
of leaky integrate-and-fire neurons (LIFs) receiving some common slowly
filtered white noise. In particular, the auto- and cross-correlation functions
of the output spike trains of pairs of cells are obtained from an improvement
of the adiabatic approximation introduced in \cite{Mor+04}. These two functions
define the firing variability and firing synchronization between neurons, and
are of much importance for understanding neuron communication.Comment: 5 pages, 3 figure
Response of Spiking Neurons to Correlated Inputs
The effect of a temporally correlated afferent current on the firing rate of
a leaky integrate-and-fire (LIF) neuron is studied. This current is
characterized in terms of rates, auto and cross-correlations, and correlation
time scale of excitatory and inhibitory inputs. The output rate
is calculated in the Fokker-Planck (FP) formalism in the limit of
both small and large compared to the membrane time constant of
the neuron. By simulations we check the analytical results, provide an
interpolation valid for all and study the neuron's response to rapid
changes in the correlation magnitude.Comment: 4 pages, 3 figure
Motif Statistics and Spike Correlations in Neuronal Networks
Motifs are patterns of subgraphs of complex networks. We studied the impact
of such patterns of connectivity on the level of correlated, or synchronized,
spiking activity among pairs of cells in a recurrent network model of integrate
and fire neurons. For a range of network architectures, we find that the
pairwise correlation coefficients, averaged across the network, can be closely
approximated using only three statistics of network connectivity. These are the
overall network connection probability and the frequencies of two second-order
motifs: diverging motifs, in which one cell provides input to two others, and
chain motifs, in which two cells are connected via a third intermediary cell.
Specifically, the prevalence of diverging and chain motifs tends to increase
correlation. Our method is based on linear response theory, which enables us to
express spiking statistics using linear algebra, and a resumming technique,
which extrapolates from second order motifs to predict the overall effect of
coupling on network correlation. Our motif-based results seek to isolate the
effect of network architecture perturbatively from a known network state
Mutual Information of Population Codes and Distance Measures in Probability Space
We studied the mutual information between a stimulus and a large system
consisting of stochastic, statistically independent elements that respond to a
stimulus. The Mutual Information (MI) of the system saturates exponentially
with system size. A theory of the rate of saturation of the MI is developed. We
show that this rate is controlled by a distance function between the response
probabilities induced by different stimuli. This function, which we term the
{\it Confusion Distance} between two probabilities, is related to the Renyi
-Information.Comment: 11 pages, 3 figures, accepted to PR
A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
We report five Local Volume dwarf galaxies (two of which are presented here
for the first time) uncovered during a comprehensive archival search for
optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC
population of HI clouds are thought to be candidate gas-rich, low mass halos at
the edge of the Local Group and beyond, but no comprehensive search for stellar
counterparts to these systems has been presented. Careful visual inspection of
all publicly available optical and ultraviolet imaging at the position of the
UCHVCs revealed six blue, diffuse counterparts with a morphology consistent
with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all
six candidate dwarf counterparts show that five have an H-derived
velocity consistent with the coincident HI cloud, confirming their association,
the sixth diffuse counterpart is likely a background object. The size and
luminosity of the UCHVC dwarfs is consistent with other known Local Volume
dwarf irregular galaxies. The gas fraction () of the five
dwarfs are generally consistent with that of dwarf irregular galaxies in the
Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC
HVC274.68+74.70123) has a very high 40. Despite the
heterogenous nature of our search, we demonstrate that the current dwarf
companions to UCHVCs are at the edge of detectability due to their low surface
brightness, and that deeper searches are likely to find more stellar systems.
If more sensitive searches do not reveal further stellar counterparts to
UCHVCs, then the dearth of such systems around the Local Group may be in
conflict with CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte
Prevalence of Bartonella henselae in blood donors and risk of blood transmission in Chile
Indexación: Scopus; Scielo.Bartonella henselae es el agente causal de la enfermedad del arañazo del gato en personas inmunocompetentes y de la angiomatosis bacilar y peliosis hepatis en inmunocomprometidos. En Chile la prevalencia de anticuerpos contra B. henselae en niños y adolescentes sanos es de 13,3%, en personas con riesgo ocupacional 60,5% y en gatos 85,6%. No existen datos publicados respecto de la seroprevalencia en donantes de sangre en nuestro paÃs, por lo que determinar si B. henselae se encuentra presente en la sangre de los donantes al momento de la donación es muy importante, ya que este microorganismo puede sobrevivir hasta 35 dÃas en los eritrocitos almacenados en banco de sangre a 4 °C.
Objetivo:
Determinar la prevalencia de B. henselae en donantes de sangre.
MetodologÃa:
Se analizaron 140 muestras de sangre de donantes, para detectar la presencia de B. henselae, utilizando la técnica de la reacción de polimerasa en cadena (RPC).
Resultados:
Se obtuvo 13,6% de los donantes de sangre con RPC positiva para la B. henselae. La secuencia de los fragmentos amplificados presentó una identidad por sobre 98% con respecto a secuencias de B. henselae de referencia.
Conclusión:
El riesgo de transmisión sanguÃnea debiera ser considerado en un paÃs con alta seroprevalencia de infección por B. henselae.Bartonella henselae is the causal agent of cat scratch disease in immunocompetent persons and bacterial angiomatosis in immunocompromised patients. In Chile, the prevalence of antibodies against B. henselae in healthy children and adolescents is 13.3%, in persons with occupational risk 60.5%, and in cats 85.6%. There are no published data regarding the seroprevalence in blood donors in our country, so determining if B. henselae is present in the blood of donors at the time of donation is very important, since this microorganism can survive up to 35 days in the red blood cells stored in a blood bank at 4 °C.
Objective:
To determine the prevalence of B. henselae in blood donors.
Methodology:
140 donor blood samples were analyzed to detect the presence of B. henselae, using the polymerase chain reaction technique.
Results:
13.6% of the blood donors with positive polymerase chain reaction for B. henselae were obtained. The sequence of the amplified fragments showed an identity of over 98% with respect to B. henselae reference sequences.
Conclusion:
The risk of blood transmission is due to a country with high B. henselae infection.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-10182017000600539&lng=en&nrm=iso&tlng=e
Emergence of an abstract categorical code enabling the discrimination of temporally structured tactile stimuli
The problem of neural coding in perceptual decision making revolves around two fundamental questions: (i) How are the neural representations of sensory stimuli related to perception, and (ii) what attributes of these neural responses are relevant for downstream networks, and how do they influence decision making? We studied these two questions by recording neurons in primary somatosensory (S1) and dorsal premotor (DPC) cortex while trained monkeys reported whether the temporal pattern structure of two sequential vibrotactile stimuli (of equal mean frequency) was the same or different. We found that S1 neurons coded the temporal patterns in a literal way and only during the stimulation periods and did not reflect the monkeys' decisions. In contrast, DPC neurons coded the stimulus patterns as broader categories and signaled them during the working memory, comparison, and decision periods. These results show that the initial sensory representation is transformed into an intermediate, more abstract categorical code that combines past and present information to ultimately generate a perceptually informed choiceThis work was supported in part by the Dirección de Asuntos del Personal Académico de la Universidad Nacional Autónoma de México and Consejo Nacional de Ciencia y TecnologÃa (R.R.) and Grant FIS2015-67876-P (to N.P.
Desarrollo de una ecuación matemática para el control de los carotenoides en el proceso de refinación del aceite crudo de palma en Venezuela
The objective of the present study is to control the factors that allow the stability of tcarotenoids during the refining process of crude palm oil in Venezuela. The correlation and interaction that exist among these factors were analyzed, through the experiment design. Two levels and several treatments were managed in order to obtain the desired correlation, which allows a greater domain of the refining process with favorable results in the retention of carotenes in the oil. The factors studied by the implementation of a design of factorial experiment 23 were: % of bleaching earth, temperature, and time in the deodorizer. The resulting individual effects as: Temperature (A), and Time (B), were significant, as well as the interaction temperature-time (AB) for an α of 0.05.El presente estudio tiene como objetivo controlar los factores que permitan la estabilidad de los carotenoides en el proceso de refinación del aceite crudo de palma en Venezuela. Se analizó la correlación e interacción que existen entre dichos factores, a través del diseño de experimento, por lo cual se manejaron dos niveles y varios tratamientos para obtener la correlación buscada, permitiendo finalmente un mayor dominio del proceso de refinación con resultados favorables en la retención de los carotenos del aceite. Los factores estudiados mediante la implementación de un diseño de experimento factorial 23 fueron % de tierra blanqueadora, temperatura y tiempo en el desodorizador. Resultando que los efectos individuales como: Temperatura (A), y Tiempo (B), fueron significantes, asà como la interacción temperatura-tiempo (AB) para un α de 0.05
Wnt Signaling Through Nitric Oxide Synthase Promotes the Formation of Multi-Innervated Spines
Structural plasticity of synapses correlates with changes in synaptic strength. Dynamic modifications in dendritic spine number and size are crucial for long-term potentiation (LTP), the cellular correlate of learning and memory. Recent studies have suggested the generation of multi-innervated spines (MIS), in the form of several excitatory presynaptic inputs onto one spine, are crucial for hippocampal memory storage. However, little is known about the molecular mechanisms underlying MIS formation and their contribution to LTP. Using 3D enhanced resolution confocal images, we examined the contribution of Wnt synaptic modulators in MIS formation in the context of LTP. We show that blockage of endogenous Wnts with specific Wnt antagonists supresses the formation of MIS upon chemical LTP induction in cultured hippocampal neurons. Gain- and loss-of-function studies demonstrate that Wnt7a signaling promotes MIS formation through the postsynaptic Wnt scaffold protein Disheveled 1 (Dvl1) by stimulating neuronal nitric oxide (NO) synthase (nNOS). Subsequently, NO activates soluble guanylyl cyclase (sGC) to increase MIS formation. Consistently, we observed an enhanced frequency and amplitude of excitatory postsynaptic currents. Collectively, our findings identify a unique role for Wnt secreted proteins through nNOS/NO/sGC signaling to modulate MIS formation during LTP
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