Buffer Phenomenon Research Articles

Social Buffering of PTSD: Longitudinal Effects and Neural Mediators

BackgroundPost-traumatic stress disorder (PTSD) is a well characterized psychiatric disorder featuring changes in mood and arousal following traumatic events. Prior animal and human studies on social support in the peri-traumatic window demonstrate a buffering effect with regards to acute biological and psychological stress symptoms. Fewer studies have explored the magnitude and mechanism on how early, post-trauma social support can reduce longitudinal PTSD severity. MethodsIn this study we investigated the beneficial impact of social support on longitudinal PTSD symptoms, and probed brain regions sensitive to this buffering phenomenon, such as the amygdala and ventromedial prefrontal cortex. In the multi-site AURORA study, n=315 participants reported PTSD symptoms (PCL-5) and perceived emotional support (PROMIS) at 2-weeks, 8-weeks, 3-months, and 6-months post-ED visit. Additionally, neuroimaging data was collected at 2 weeks post trauma. ResultsWe hypothesized that early, post-trauma social support would be linked with greater fractional anisotropic (FA) values in white matter tracts that have known connectivity between the amygdala and prefrontal cortex and would predict reduced neural reactivity to social threat cues in the amygdala. Interestingly, while we observed greater FA in the bilateral cingulum and bilateral uncinate fasciculus as a function of early post-trauma emotional support, we also identified greater threat reactivity in the precuneus/posterior cingulate, a component of the default mode network. ConclusionOur findings suggest that the neurocircuitry underlying the response to social threat cues are facilitated through broader pathways that involve the posterior hub of the default mode network.

PERIOD Phosphoclusters Control Temperature Compensation of the Drosophila Circadian Clock.

Ambient temperature varies constantly. However, the period of circadian pacemakers is remarkably stable over a wide-range of ecologically- and physiologically-relevant temperatures, even though the kinetics of most biochemical reactions accelerates as temperature rises. This thermal buffering phenomenon, called temperature compensation, is a critical feature of circadian rhythms, but how it is achieved remains elusive. Here, we uncovered the important role played by the Drosophila PERIOD (PER) phosphodegron in temperature compensation. This phosphorylation hotspot is crucial for PER proteasomal degradation and is the functional homolog of mammalian PER2 S478 phosphodegron, which also impacts temperature compensation. Using CRISPR-Cas9, we introduced a series of mutations that altered three Serines of the PER phosphodegron. While all three Serine to Alanine substitutions lengthened period at all temperatures tested, temperature compensation was differentially affected. S44A and S45A substitutions caused undercompensation, while S47A resulted in overcompensation. These results thus reveal unexpected functional heterogeneity of phosphodegron residues in thermal compensation. Furthermore, mutations impairing phosphorylation of the per s phosphocluster showed undercompensation, consistent with its inhibitory role on S47 phosphorylation. We observed that S47A substitution caused increased accumulation of hyper-phosphorylated PER at warmer temperatures. This finding was corroborated by cell culture assays in which S47A slowed down phosphorylation-dependent PER degradation at high temperatures, causing PER degradation to be excessively temperature-compensated. Thus, our results point to a novel role of the PER phosphodegron in temperature compensation through temperature-dependent modulation of the abundance of hyper-phosphorylated PER. Our work reveals interesting mechanistic convergences and differences between mammalian and Drosophila temperature compensation of the circadian clock.

A PC-tool to calculate the Moisture Buffer Value

Hygroscopic building materials have the ability to moderate the relative humidity variation without the need for active systems. The moisture buffer phenomenon can be assessed by way of the Moisture Buffer Value (MBV). Some authors have pointed out that the MBV is sensitive to several parameters, however, there is no model that involves all them.The aim of the developed PC-tool is to take into account all these variables to calculate the MBV of hygroscopic building materials. The material hygroscopic properties will be needed to solve the moisture storage and transport inside the porous materials and consequently to predict its MBV.

Buffered Autoregressive Models With Conditional Heteroscedasticity: An Application to Exchange Rates

This article introduces a new model called the buffered autoregressive model with generalized autoregressive conditional heteroscedasticity (BAR-GARCH). The proposed model, as an extension of the BAR model in Li et al. (2015), can capture the buffering phenomena of time series in both the conditional mean and variance. Thus, it provides us a new way to study the nonlinearity of time series. Compared with the existing AR-GARCH and threshold AR-GARCH models, an application to several exchange rates highlights the importance of the BAR-GARCH model.

Existence and stability of periodic solutions of quasi-linear Korteweg — de Vries equation

We consider the scalar nonlinear differential-difference equation with two delays, which models electrical activity of a neuron. Under some additional suppositions for this equation well known method of quasi-normal forms can be applied. Its essence lies in the formal normalization of the Poincare – Dulac obtaining quasi-normal form and the subsequent application of the theorems of conformity. In this case, the result of the application of quasi-normal forms is a countable system of differential-difference equations, which can be turned into a boundary value problem of the Korteweg – de Vries equation. The investigation of this boundary value problem allows us to draw a conclusion about the behaviour of the original equation. Namely, for a suitable choice of parameters in the framework of this equation is implemented buffer phenomenon consisting in the presence of the bifurcation mechanism for the birth of an arbitrarily large number of stable cycles.

On Buffered Double Autoregressive Time Series Models

A buffered double autoregressive (BDAR) time series model is proposed in this paper to depict the buffering phenomenon of conditional mean and conditional variance in time series. To build this model, a novel flexible regime switch mechanism is introduced to modify the classical threshold AR model by capturing the stickiness of signal. Besides, considering the inadequacy of traditional models under the lack of information, a signal retrospection is run in this model to provide a more accurate judgement. Moreover, formal proofs suggest strict stationarity and geometric ergodicity of BDAR model under several sufficient conditions. A Gaussian quasi-maximum likelihood estimation (QMLE) is employed to compute the estimators in this model. The strict proof reveals the asymptotic normality of the estimated coefficients of double AR models. More importantly, it has been demonstrated that the estimated threshold of the BDAR model weakly converges to a functional of a two-sided compound Poisson process. Furthermore, a model selection criteria and asymptotic property have been established. Simulation studies are constructed to evaluate the finite sample performance of QMLE and model selection criteria. Finally, an empirical analysis of Hang Seng Index (HSI) using BDAR model reveals the asymmetry of investors’ preference over losses and gains as well as the asymmetry of volatility structure.

Buffering in cyclic gene networks

We consider cyclic chains of unidirectionally coupled delay differential–difference equations that are mathematical models of artificial oscillating gene networks. We establish that the buffering phenomenon is realized in these system for an appropriate choice of the parameters: any given finite number of stable periodic motions of a special type, the so-called traveling waves, coexist.

Self-Sustained Relaxation Oscillations in Time-Delay Neural Systems

A new method to model the phenomena ’bursting’ and ’buffering’ in neural systems is represented. Namely, a singularly perturbed nonlinear scalar differential difference equation with two delays is introduced, which is a mathematical model of a single neuron. It is shown that for suitably chosen parameters this equation has a stable periodic solution with an arbitrary prescribed number of asymptotically high impulses (spikes) on a period interval. It is also shown that the buffering phenomenon occurs in a one-dimensional chain of diffusively coupled neurons of this type: as the number of components in the chain grows in a way compatible with a decrease of the diffusion coefficient, the number of co-existing stable periodic motions increases indefinitely.

The museum in a test tube – Adding a third dimension to the evaluation of the impact of volatile organic acids on paper

Collections of art on paper, libraries and archives in general, are striving for optimal storage conditions for cultural heritage in their deposits and exhibition facilities. Therefore, properly estimating the risk of volatile organic compounds emitted from historic and recent storage materials on paper-based collections is of utmost importance. Applying an optimized static headspace gas chromatography and mass spectrometry approach combined with cellulose-specific analysis provides insight into the potential degradation effects and mechanisms acting on two different paper samples (Whatman No.1 and historic rag paper) used as degradation indicators. Acetic and formic acid, two powerful volatile organic acids, were quantified with differing amounts, depending on the type of historic storage material tested. Molar mass and carbonyl group content were used to monitor cellulose degradation of the indicator papers. Combining these results in 3D plots helps to visualize synergies that evolve from mutual emission of acetic and formic acids. In addition, choosing between the two paper-based degradation indicators helps to evaluate different phenomena: Whatman No.1 reacts toward acid hydrolysis and is more sensitive, while rag paper helps to evaluate buffering phenomena as occurring in original materials.

Social buffering ameliorates conditioned fear responses in female rats

The stress experienced by an animal is ameliorated when the animal is exposed to distressing stimuli along with a conspecific animal(s). This is known as social buffering. Previously, we found that the presence of an unfamiliar male rat induced social buffering and ameliorated conditioned fear responses of a male rat subjected to an auditory conditioned stimulus (CS). However, because our knowledge of social buffering is highly biased towards findings in male subjects, analyses using female subjects are crucial for comprehensively understanding the social buffering phenomenon. In the present studies, we assessed social buffering of conditioned fear responses in female rats. We found that the estrus cycle did not affect the intensity of the rats' fear responses to the CS or their degree of vigilance due to the presence of a conspecific animal. Based on these findings, we then assessed whether social buffering ameliorated conditioned fear responses in female rats without taking into account their estrus cycles. When fear conditioned female rats were exposed to the CS without the presence of a conspecific, they exhibited behavioral responses, including freezing, and elevated corticosterone levels. By contrast, the presence of an unfamiliar female rat suppressed these responses. Based on these findings, we conclude that social buffering can ameliorate conditioned fear responses in female rats.

SELF-EXCITED WAVE PROCESSES IN CHAINS OF UNIDIRECTIONALLY COUPLED IMPULSE NEURONS

The article is devoted to the mathematical modeling of neural activity. We propose new classes of singularly perturbed differential-difference equations with delay of Volterra type. With these systems, the models as a single neuron or neural networks are described. We study attractors of ring systems of unidirectionally coupled impulse neurons in the case where the number of links in the system increases indefinitely. In order to study periodic solutions of travelling wave type of this system, some special tricks are used which reduce the existence and stability problems for cycles to the investigation of auxiliary system with impulse actions. Using this approach, we establish that the number of stable self-excited waves simultaneously existing in the chain increases unboundedly as the number of links of the chain increases, that is, the well-known buffer phenomenon occurs.

Social Odors: Alarm Pheromones and Social Buffering.

In this chapter, I describe 2 types of olfactory communication in rats, which appear to arouse anxiety and relief, respectively. In alarm pheromonal communication, rats release 4-methylpentanal and hexanal from their perianal region when they are stressed. These molecules activate the anxiety circuit, including the bed nucleus of the stria terminalis, when 4-methylpentanal and hexanal are simultaneously detected by the vomeronasal system and the main olfactory system, respectively. Consequently, recipient rats show a variety of anxiety responses, depending on the threatening stimuli. In appeasing olfactory communication, non-stressed rats release an appeasing olfactory signal, which is detected by the main olfactory system of other rats. When detected, this olfactory signal suppresses activation of the basolateral complex of the amygdala and, as a result, ameliorates stress responses elicited by an auditory conditioned stimulus during social buffering phenomenon. Because social buffering appears to be based on affinity and attachment to accompanying animals, the appeasing olfactory signal may arouse relief in rats. A definition of social buffering is also proposed as we still have no set definition for the term social buffering yet.

Buffering effect in continuous chains of unidirectionally coupled generators

We propose a mathematical model of a continuous annular chain of unidirectionally coupled generators given by some nonlinear advection-type hyperbolic boundary value problem. Such problems are constructed by a limit transition from annular chains of unidirectionally coupled ordinary differential equations with an unbounded increase in the number of links. We find that a certain buffering phenomenon is realized in our boundary value problem. Namely, we show that any preassigned finite number of stable periodic motions of the traveling-wave type can coexist in the model.

Buffer phenomenon and chaos in circular chains of unidirectionally coupled oscillators

Buffer phenomenon and chaos in circular chains of unidirectionally coupled oscillators

The buffer phenomenon in ring-like chains of unidirectionally connected generators

We introduce a new object, namely, a system of ordinary differential equations which is a mathematical model of a ring-like chain of unidirectionally connected RCL-generators. To study periodic solutions of travelling wave type of this system, some special tricks are used which reduce the existence and stability problems for cycles to the investigation of auxiliary delay equations. Using this approach, we establish that the number of stable travelling waves simultaneously existing in the chain increases unboundedly as the number of links of the chain increases, that is, the well-known buffer phenomenon occurs.

Autowave processes in continual chains of unidirectionally coupled oscillators

We introduce a mathematical model of a continual circular chain of unidirectionally coupled oscillators. It is a nonlinear hyperbolic boundary value problem obtained from a circular chain of unidirectionally coupled ordinary differential equations in the limit as the number of equations indefinitely increases. We study the attractors of this boundary value problem. Combining analytic and numerical methods, we establish that one of the following two alternatives takes place in this problem: either the buffer phenomenon (unbounded accumulation of stable periodic motions) or chaotic attractors of arbitrarily high Lyapunov dimensions.

On the Number of Coexisting Autowaves in the Chain of Coupled Oscillators

We consider a model of neuron complex formed by a chain of diffusion coupled oscillators. Every oscillator simulates a separate neuron and is given by a singularly perturbed nonlinear differential-difference equation with two delays. Oscillator singularity allows reduction to limit system without small parameters but with pulse external action. The statement on correspondence between the resulting system with pulse external action and the original oscillator chain gives a way to demonstrate that under consistent growth of the chain node number and decrease of diffusion coefficient we can obtain in this chain unlimited growth of its coexistent stable periodic orbits (buffer phenomenon). Numerical simulations give the actual dependence of the number of stable orbits on the diffusion parameter value.

Application of the Method of Quasi-Normal Forms to the Mathematical Model of a Single Neuron

We consider a scalar nonlinear differential-difference equation with two delays, which models the behavior of a single neuron. Under some additional suppositions for this equation it is applied a well-known method of quasi-normal forms. Its essence lies in the formal normalization of the Poincare – Dulac, the production of a quasi-normal form and the subsequent application of the conformity theorems. In this case, the result of the application of quasi-normal forms is a countable system of differential-difference equations, which manages to turn into a boundary value problem of the Korteweg – de Vries equation. The investigation of this boundary value problem allows to make the conclusion about the behavior of the original equation. Namely, for a suitable choice of parameters in the framework of this equation it is implemented the buffer phenomenon consisting in the presence of the bifurcation mechanism for the birth of an arbitrarily large number of stable cycles.

Buffer phenomenon in the generalization of the Swift-Hohenberg equation

A particular generalization of the Swift-Hohenberg equation with zero Dirichlet boundary conditions at the endpoints of a finite interval is considered. It is found that, as the length l of the interval increases while the supercriticality ɛ is fixed and sufficiently small, the number of coexisting stable equilibrium states in the boundary problem indefinitely increases; i.e., a buffer phenomenon is observed.

On a method for mathematical modeling of chemical synapses

We introduce a new mathematical model of a circular neural network with unidirectional chemical bonds. The model is a singularly perturbed system of delay differential-difference equations. We study the existence and stability of relaxation periodic motions in the system. It is proved that the well-known buffer phenomenon can occur in the model.