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Search Results: 1 - 10 of 8586 matches for " Magdalena Sarah Volz "
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Effects of Sensory Behavioral Tasks on Pain Threshold and Cortical Excitability
Magdalena Sarah Volz, Vanessa Suarez-Contreras, Mariana E. Mendonca, Fernando Santos Pinheiro, Lotfi B. Merabet, Felipe Fregni
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0052968
Abstract: Background/Objective Transcutaneous electrical stimulation has been proven to modulate nervous system activity, leading to changes in pain perception, via the peripheral sensory system, in a bottom up approach. We tested whether different sensory behavioral tasks induce significant effects in pain processing and whether these changes correlate with cortical plasticity. Methodology/Principal Findings This randomized parallel designed experiment included forty healthy right-handed males. Three different somatosensory tasks, including learning tasks with and without visual feedback and simple somatosensory input, were tested on pressure pain threshold and motor cortex excitability using transcranial magnetic stimulation (TMS). Sensory tasks induced hand-specific pain modulation effects. They increased pain thresholds of the left hand (which was the target to the sensory tasks) and decreased them in the right hand. TMS showed that somatosensory input decreased cortical excitability, as indexed by reduced MEP amplitudes and increased SICI. Although somatosensory tasks similarly altered pain thresholds and cortical excitability, there was no significant correlation between these variables and only the visual feedback task showed significant somatosensory learning. Conclusions/Significance Lack of correlation between cortical excitability and pain thresholds and lack of differential effects across tasks, but significant changes in pain thresholds suggest that analgesic effects of somatosensory tasks are not primarily associated with motor cortical neural mechanisms, thus, suggesting that subcortical neural circuits and/or spinal cord are involved with the observed effects. Identifying the neural mechanisms of somatosensory stimulation on pain may open novel possibilities for combining different targeted therapies for pain control.
Neurobiological Effects of Transcranial Direct Current Stimulation: A Review
Liciane Fernandes Medeiros,Izabel Cristina Custodio de Souza,Liliane Pinto Vidor,Andressa de Souza,Alícia Deitos,Magdalena Sarah Volz,Felipe Fregni,Wolnei Caumo,Iraci L. S. Torres
Frontiers in Psychiatry , 2012, DOI: 10.3389/fpsyt.2012.00110
Abstract: Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation technique that is affordable and easy to operate compared to other neuromodulation techniques. Anodal stimulation increases cortical excitability, while the cathodal stimulation decreases it. Although tDCS is a promising treatment approach for chronic pain as well as for neuropsychiatric diseases and other neurological disorders, several complex neurobiological mechanisms that are not well understood are involved in its effect. The purpose of this systematic review is to summarize the current knowledge regarding the neurobiological mechanisms involved in the effects of tDCS. The initial search resulted in 171 articles. After applying inclusion and exclusion criteria, we screened 32 full-text articles to extract findings about the neurobiology of tDCS effects including investigation of cortical excitability parameters. Overall, these findings show that tDCS involves a cascade of events at the cellular and molecular levels. Moreover, tDCS is associated with glutamatergic, GABAergic, dopaminergic, serotonergic, and cholinergic activity modulation. Though these studies provide important advancements toward the understanding of mechanisms underlying tDCS effects, further studies are needed to integrate these mechanisms as to optimize clinical development of tDCS.
Dissociation of Motor Task-Induced Cortical Excitability and Pain Perception Changes in Healthy Volunteers
Magdalena S. Volz, Mariana Mendonca, Fernando S. Pinheiro, Huashun Cui, Marcus Santana, Felipe Fregni
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0034273
Abstract: Background There is evidence that interventions aiming at modulation of the motor cortex activity lead to pain reduction. In order to understand further the role of the motor cortex on pain modulation, we aimed to compare the behavioral (pressure pain threshold) and neurophysiological effects (transcranial magnetic stimulation (TMS) induced cortical excitability) across three different motor tasks. Methodology/Principal Findings Fifteen healthy male subjects were enrolled in this randomized, controlled, blinded, cross-over designed study. Three different tasks were tested including motor learning with and without visual feedback, and simple hand movements. Cortical excitability was assessed using single and paired-pulse TMS measures such as resting motor threshold (RMT), motor-evoked potential (MEP), intracortical facilitation (ICF), short intracortical inhibition (SICI), and cortical silent period (CSP). All tasks showed significant reduction in pain perception represented by an increase in pressure pain threshold compared to the control condition (untrained hand). ANOVA indicated a difference among the three tasks regarding motor cortex excitability change. There was a significant increase in motor cortex excitability (as indexed by MEP increase and CSP shortening) for the simple hand movements. Conclusions/Significance Although different motor tasks involving motor learning with and without visual feedback and simple hand movements appear to change pain perception similarly, it is likely that the neural mechanisms might not be the same as evidenced by differential effects in motor cortex excitability induced by these tasks. In addition, TMS-indexed motor excitability measures are not likely good markers to index the effects of motor-based tasks on pain perception in healthy subjects as other neural networks besides primary motor cortex might be involved with pain modulation during motor training.
Random Networks with Tunable Degree Distribution and Clustering
Erik Volz
Physics , 2004, DOI: 10.1103/PhysRevE.70.056115
Abstract: We present an algorithm for generating random networks with arbitrary degree distribution and Clustering (frequency of triadic closure). We use this algorithm to generate networks with exponential, power law, and poisson degree distributions with variable levels of clustering. Such networks may be used as models of social networks and as a testable null hypothesis about network structure. Finally, we explore the effects of clustering on the point of the phase transition where a giant component forms in a random network, and on the size of the giant component. Some analysis of these effects is presented.
SIR dynamics in structured populations with heterogeneous connectivity
Erik Volz
Physics , 2005,
Abstract: Most epidemic models assume equal mixing among members of a population. An alternative approach is to model a population as random network in which individuals may have heterogeneous connectivity. This paper builds on previous research by describing the exact dynamical behavior of epidemics as they occur in random networks. A system of nonlinear differential equations is presented which describes the behavior of epidemics spreading through random networks with arbitrary degree distributions. The degree distribution is observed to have significant impact on both the final size and time scale of epidemics.
Tomography of random social networks
Erik Volz
Physics , 2005,
Abstract: We study the statistical properties of large random networks with specified degree distributions. New techniques are presented for analyzing the structure of social networks. Specifically, we address the question of how many nodes exist at a distance from a given node. We also explore the degree distribution of for nodes at some distance from a given node. Implications for network sampling and diffusion on social networks are described.
A Note on Topology Preservation in Classification, and the Construction of a Universal Neuron Grid
Dietmar Volz
Physics , 2013,
Abstract: It will be shown that according to theorems of K. Menger, every neuron grid if identified with a curve is able to preserve the adopted qualitative structure of a data space. Furthermore, if this identification is made, the neuron grid structure can always be mapped to a subset of a universal neuron grid which is constructable in three space dimensions. Conclusions will be drawn for established neuron grid types as well as neural fields.
SIR dynamics in random networks with heterogeneous connectivity
Erik Volz
Quantitative Biology , 2007,
Abstract: Random networks with specified degree distributions have been proposed as realistic models of population structure, yet the problem of dynamically modeling SIR-type epidemics in random networks remains complex. I resolve this dilemma by showing how the SIR dynamics can be modeled with a system of three nonlinear ODE's. The method makes use of the probability generating function (PGF) formalism for representing the degree distribution of a random network and makes use of network-centric quantities such as the number of edges in a well-defined category rather than node-centric quantities such as the number of infecteds or susceptibles. The PGF provides a simple means of translating between network and node-centric variables and determining the epidemic incidence at any time. The theory also provides a simple means of tracking the evolution of the degree distribution among susceptibles or infecteds. The equations are used to demonstrate the dramatic effects that the degree distribution plays on the final size of an epidemic as well as the speed with which it spreads through the population. Power law degree distributions are observed to generate an almost immediate expansion phase yet have a smaller final size compared to homogeneous degree distributions such as the Poisson. The equations are compared to stochastic simulations, which show good agreement with the theory. Finally, the dynamic equations provide an alternative way of determining the epidemic threshold where large-scale epidemics are expected to occur, and below which epidemic behavior is limited to finite-sized outbreaks.
The Leukocyte Receptor Complex in Chicken Is Characterized by Massive Expansion and Diversification of Immunoglobulin-Like Loci
Katja Laun,Penny Coggill,Sophie Palmer,Sarah Sims,Zemin Ning,Jiannis Ragoussis,Emanuela Volpi,Natalie Wilson,Stephan Beck,Andreas Ziegler ,Armin Volz
PLOS Genetics , 2006, DOI: 10.1371/journal.pgen.0020073
Abstract: The innate and adaptive immune systems of vertebrates possess complementary, but intertwined functions within immune responses. Receptors of the mammalian innate immune system play an essential role in the detection of infected or transformed cells and are vital for the initiation and regulation of a full adaptive immune response. The genes for several of these receptors are clustered within the leukocyte receptor complex (LRC). The purpose of this study was to carry out a detailed analysis of the chicken (Gallus gallus domesticus) LRC. Bacterial artificial chromosomes containing genes related to mammalian leukocyte immunoglobulin-like receptors were identified in a chicken genomic library and shown to map to a single microchromosome. Sequencing revealed 103 chicken immunoglobulin-like receptor (CHIR) loci (22 inhibitory, 25 activating, 15 bifunctional, and 41 pseudogenes). A very complex splicing pattern was found using transcript analyses and seven hypervariable regions were detected in the external CHIR domains. Phylogenetic and genomic analysis showed that CHIR genes evolved mainly by block duplications from an ancestral inhibitory receptor locus, with transformation into activating receptors occurring more than once. Evolutionary selection pressure has led not only to an exceptional expansion of the CHIR cluster but also to a dramatic diversification of CHIR loci and haplotypes. This indicates that CHIRs have the potential to complement the adaptive immune system in fighting pathogens.
A National Case-Control Study Identifies Human Socio-Economic Status and Activities as Risk Factors for Tick-Borne Encephalitis in Poland
Pawel Stefanoff, Magdalena Rosinska, Steven Samuels, Dennis J. White, Dale L. Morse, Sarah E. Randolph
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0045511
Abstract: Background Tick-borne encephalitis (TBE) is endemic to Europe and medically highly significant. This study, focused on Poland, investigated individual risk factors for TBE symptomatic infection. Methods and Findings In a nation-wide population-based case-control study, of the 351 TBE cases reported to local health departments in Poland in 2009, 178 were included in the analysis. For controls, of 2704 subjects (matched to cases by age, sex, district of residence) selected at random from the national population register, two were interviewed for each case and a total of 327 were suitable for the analysis. Questionnaires yielded information on potential exposure to ticks during the six weeks (maximum incubation period) preceding disease onset in each case. Independent associations between disease and socio-economic factors and occupational or recreational exposure were assessed by conditional logistic regression, stratified according to residence in known endemic and non-endemic areas. Adjusted population attributable fractions (PAF) were computed for significant variables. In endemic areas, highest TBE risk was associated with spending ≥10 hours/week in mixed forests and harvesting forest foods (adjusted odds ratio 19.19 [95% CI: 1.72–214.32]; PAF 0.127 [0.064–0.193]), being unemployed (11.51 [2.84–46.59]; 0.109 [0.046–0.174]), or employed as a forester (8.96 [1.58–50.77]; 0.053 [0.011–0.100]) or non-specialized worker (5.39 [2.21–13.16]; 0.202 [0.090–0.282]). Other activities (swimming, camping and travel to non-endemic regions) reduced risk. Outside TBE endemic areas, risk was greater for those who spent ≥10 hours/week on recreation in mixed forests (7.18 [1.90–27.08]; 0.191 [0.065–0.304]) and visited known TBE endemic areas (4.65 [0.59–36.50]; 0.058 [?0.007–0.144]), while travel to other non-endemic areas reduced risk. Conclusions These socio-economic factors and associated human activities identified as risk factors for symptomatic TBE in Poland are consistent with results from previous correlational studies across eastern Europe, and allow public health interventions to be targeted at particularly vulnerable sections of the population.
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