Dynamics of Coupled Noisy Neural Oscillators with Heterogeneous Phase Resetting Curves

Pulse-coupled phase oscillators have been utilized in a variety of contexts. Motivated by neuroscience, we study a network of pulse-coupled phase oscillators receiving independent and correlated noise. An additional physiological attribute, heterogeneity, is incorporated in the phase resetting curve (PRC), which is a vital entity for modeling the biophysical dynamics of oscillators. An accurate probability density or mean field description is large dimensional, requiring reduction methods for tractability. We present a reduction method to capture the pairwise synchrony via the probability density of the phase differences, and explore the robustness of the method. We find the reduced methods can capture some of the synchronous dynamics in these networks. The variance of the noisy period (or spike times) in this network is also considered. In particular, we find phase oscillators with predominately positive PRCs (type 1) have larger variance with inhibitory pulse- coupling than PRCs with a larger negative regions (type 2), but with excitatory pulse-coupling the opposite happens – type 1 oscillators have lower variability than type 2. Analysis of this phenomena is provided via an asymptotic approximation with weak noise and weak coupling, where we demonstrate how the individual PRC alters variability with pulse-coupling. We make comparisons of the phase oscillators to full oscillator networks and discuss the utility and shortcomings

One-Dimensional Population Density Approaches to Recurrently Coupled Networks of Neurons with Noise

Mean-field systems have been previously derived for networks of coupled, two-dimensional, integrate-and-fire neurons such as the Izhikevich, adapting exponential (AdEx) and quartic integrate and fire (QIF), among others. Unfortunately, the mean-field systems have a degree of frequency error and the networks analyzed often do not include noise when there is adaptation. Here, we derive a one-dimensional partial differential equation (PDE) approximation for the marginal voltage density under a first order moment closure for coupled networks of integrate-and-fire neurons with white noise inputs. The PDE has substantially less frequency error than the mean-field system, and provides a great deal more information, at the cost of analytical tractability. The convergence properties of the mean-field system in the low noise limit are elucidated. A novel method for the analysis of the stability of the asynchronous tonic firing solution is also presented and implemented. Unlike previous attempts at stability analysis with these network types, information about the marginal densities of the adaptation variables is used. This method can in principle be applied to other systems with nonlinear partial differential equations.Comment: 26 Pages, 6 Figure

From customer orientation to customer satisfaction: The gap between theory and practice

The classical quality management theory suggests that different quality improvement practices have a similar positive effect on overall operational efficiency, leading to customer satisfaction. Based on a study of 225 organizations in the electronics industry in Hong Kong, we find that individual quality improvement practice has a specific effect on operational performance, rather than equally improving the overall operational efficiency. Our investigations indicate that customer orientation practices primarily affect time-based efficiency, while process improvement efforts help cost-related performance. On the other hand, emphasizing process-control systems leads to customer satisfaction directly without necessarily improving operations. While supporting the basic assertions of the classical quality management theory, these findings reveal that several problems exist in the practice of quality management in industry, and suggest that a re-direction of several quality management practices seems necessary. This research refines the understanding of quality management by explicating the specific effect of customer orientation and process management on organizational performance.published_or_final_versio

From customer orientation to customer satisfaction : the gap between theory and practice

2003-2004 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Asymptomatic members with SOD1 mutation in a large kindred with familial amyotrophic lateral sclerosis have abnormal water diffusion characterisitcs

DTI was carried out in FALS/SALS patients and familial members with SOD1 mutation (AFALS) who may be in a pre-symptomatic phase of ALS. The changes in FA and TT were investigated in CBT/CST and in whole brain. In FALS/SALS, diffusion pattern changes were found in cerebral peduncle, internal capsule, sub-cortical white matter, cerebellum and frontal lobe while in AFALS, abnormal pattern could also be detected in the cerebral peduncle, cerebellum and frontal lobe but with a smaller extent. Our study indicates that DTI can show early diffusion changes in members with SOD1 mutation in FALS prior to symptom-onset.published_or_final_versio

Distribution and Redistribution of HIV-1 Nucleocapsid Protein in Immature, Mature, and Integrase-Inhibited Virions: a Role for Integrase in Maturation

During virion maturation, HIV-1 capsid protein assembles into a conical core containing the viral ribonucleoprotein (vRNP) complex, thought to be composed mainly of the viral RNA and nucleocapsid protein (NC). After infection, the viral RNA is reverse transcribed into double-stranded DNA, which is then incorporated into host chromosomes by integrase (IN) catalysis. Certain IN mutations (class II) and antiviral drugs (allosteric IN inhibitors [ALLINIs]) adversely affect maturation, resulting in virions that contain “eccentric condensates,” electron-dense aggregates located outside seemingly empty capsids. Here we demonstrate that in addition to this mislocalization of electron density, a class II IN mutation and ALLINIs each increase the fraction of virions with malformed capsids (from ∼12% to ∼53%). Eccentric condensates have a high NC content, as demonstrated by “tomo-bubblegram” imaging, a novel labeling technique that exploits the susceptibility of NC to radiation damage. Tomo-bubblegrams also localized NC inside wild-type cores and lining the spherical Gag shell in immature virions. We conclude that eccentric condensates represent nonpackaged vRNPs and that either genetic or pharmacological inhibition of IN can impair vRNP incorporation into mature cores. Supplying IN in trans as part of a Vpr-IN fusion protein partially restored the formation of conical cores with internal electron density and the infectivity of a class II IN deletion mutant virus. Moreover, the ability of ALLINIs to induce eccentric condensate formation required both IN and viral RNA. Based on these observations, we propose a role for IN in initiating core morphogenesis and vRNP incorporation into the mature core during HIV-1 maturation

PM2.5 Exposure Suppresses Dendritic Maturation in Subgranular Zone in Aged Rats

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