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Search Results: 1 - 10 of 219528 matches for " Mya C. Schiess "
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α-Synuclein and Anti-α-Synuclein Antibodies in Parkinson’s Disease, Atypical Parkinson Syndromes, REM Sleep Behavior Disorder, and Healthy Controls
Lynnae M. Smith, Mya C. Schiess, Mary P. Coffey, Andrea C. Klaver, David A. Loeffler
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0052285
Abstract: α-synuclein is thought to play a key role in Parkinson’s disease (PD) because it is the major protein in Lewy bodies, and because its gene mutations, duplication, and triplication are associated with early-onset PD. There are conflicting reports as to whether serum and plasma concentrations of α-synuclein and anti-α-synuclein antibodies differ between PD and control subjects. The objectives of this study were to compare the levels of α-synuclein and its antibodies between individuals with typical PD (n = 14), atypical Parkinson syndromes (n = 11), idiopathic rapid eye movement sleep behavior disorder (n = 10), and healthy controls (n = 9), to assess the strength of association between these serum proteins, and to determine group sizes needed for a high probability (80% power) of detecting statistical significance for 25% or 50% differences between typical PD and control subjects for these measurements. Analysis of log-transformed data found no statistically significant differences between groups for either α-synuclein or its antibodies. The concentrations of these proteins were weakly correlated (Spearman rho = 0.16). In subjects with typical PD and atypical Parkinson syndromes, anti-α-synuclein antibody levels above 1.5 μg/ml were detected only in subjects with no more than four years of clinical disease. Power analysis indicated that 236 and 73 samples per group would be required for an 80% probability that 25% and 50% differences, respectively, in mean α-synuclein levels between typical PD and control subjects would be statistically significant; for anti-α-synuclein antibodies, 283 and 87 samples per group would be required. Our findings are consistent with those previous studies which suggested that serum concentrations of α-synuclein and its antibodies are not significantly altered in PD.
CSF from Parkinson disease Patients Differentially Affects Cultured Microglia and Astrocytes
Mya C Schiess, Jennifer L Barnes, Timothy M Ellmore, Brian J Poindexter, Kha Dinh, Roger J Bick
BMC Neuroscience , 2010, DOI: 10.1186/1471-2202-11-151
Abstract: After PD-CSF treatment, microglia growth was reduced extensively, and a non-confluent pattern with morphological changes developed, that was not evident in disease control CSF and no-CSF treated cultures. Astrocyte growth rates were similarly reduced by exposure to PD-CSF, but morphological changes were not consistently noted. PD-CSF treated microglia showed a significant increase in α-synuclein content by day 4 compared to other treatments (p ≤ 0.02). In microglia only, α-synuclein aggregated and redistributed to peri-nuclear locations.Cultured microglia and astrocytes are differentially affected by PD-CSF exposure compared to non-PD-CSF controls. PD-CSF dramatically impacts microglia cell growth, morphology, and α-synuclein deposition compared to astrocytes, supporting the hypothesis of cell specific susceptibility to PD-CSF toxicity.Evidence of increased levels of specific cytokines and growth factors within nigrostriatal dopamine regions of the brain in Parkinson's disease (PD) patients, has led to the belief that PD is the result of immunological responses that promote an increased synthesis and release of proinflammatory cytokines [1-3]. These cytokines have been shown to affect the quantity and distribution of intracellular proteins such as α-synuclein in cultured microglia [4]. The exact function of α-synuclein is unknown. However, there is evidence supporting a vesicular, pre-synaptic role for α-synuclein in the dopamine transporter system [5-7]. This normally soluble protein is recognized to be a large component of the Lewy body, the pathologic hallmark of the disease. What promotes the formation of Lewy body inclusions is poorly understood, but it has been proposed that this is a protective pathway in response to failed mechanisms, such as aggresome degradation of dysfunctional protein [8]. The Lewy body, and its precursor the Lewy neurite, have been reproducibly traced through the CNS, resulting in a progressive and predictable pattern of involvement lea
QoE Assessment of Fairness between Players in Networked Virtual 3D Objects Identification Game Using Haptic, Olfactory, and Auditory Senses  [PDF]
Ryo Arima, Mya Sithu, Yutaka Ishibashi
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2017, DOI: 10.4236/ijcns.2017.107007
Abstract:
In this paper, we carry out QoE (Quality of Experience) assessment to investigate influences of olfactory and auditory senses on fairness for a networked virtual 3D object identification game with haptics. In the game, two players try to identify objects which are placed in a shared 3D virtual space. In the assessment, we carry out the game in four cases. Smells and sounds are presented in the first case, only sounds are done in the second case, and only smells are done in the third case. In the last case, we present neither smell nor sound. As a result, we demonstrate that the fairness deteriorates more largely as the difference in conditions between two users becomes larger.
A microscopic view of accelerated dynamics in deformed polymer glasses
Mya Warren,Joerg Rottler
Physics , 2010, DOI: 10.1103/PhysRevLett.104.205501
Abstract: A molecular level analysis of segmental trajectories obtained from molecular dynamics simulations is used to obtain the full relaxation time spectrum in aging polymer glasses subject to three different deformation protocols. As in experiments, dynamics can be accelerated by several orders of magnitude, and a narrowing of the distribution of relaxation times during creep is directly observed. Additionally, the acceleration factor describing the transformation of the relaxation time distributions is computed and found to obey a universal dependence on the global strain, independent of age and deformation protocol.
Mechanical rejuvenation and over-aging in the soft glassy rheology model
Mya Warren,Joerg Rottler
Physics , 2008, DOI: 10.1103/PhysRevE.78.041502
Abstract: Mechanical rejuvenation and over-aging of glasses is investigated through stochastic simulations of the soft glassy rheology (SGR) model. Strain- and stress-controlled deformation cycles for a wide range of loading conditions are analyzed and compared to molecular dynamics simulations of a model polymer glass. Results indicate that deformation causes predominantly rejuvenation, whereas over-aging occurs only at very low temperature, small strains, and for high initial energy states. Although the creep compliance in the SGR model exhibits full aging independent of applied load, large stresses in the nonlinear creep regime cause configurational changes leading to rejuvenation of the relaxation time spectrum probed after a stress cycle. During recovery, however, the rejuvenated state rapidly returns to the original aging trajectory due to collective relaxations of the internal strain.
Deformation-induced accelerated dynamics in polymer glasses
Mya Warren,Joerg Rottler
Physics , 2010, DOI: 10.1063/1.3505149
Abstract: Molecular dynamics simulations are used to investigate the effects of deformation on the segmental dynamics in an aging polymer glass. Individual particle trajectories are decomposed into a series of discontinuous hops, from which we obtain the full distribution of relaxation times and displacements under three deformation protocols: step stress (creep), step strain, and constant strain rate deformation. As in experiments, the dynamics can be accelerated by several orders of magnitude during deformation, and the history dependence is entirely erased during yield (mechanical rejuvenation). Aging can be explained as a result of the long tails in the relaxation time distribution of the glass, and similarly, mechanical rejuvenation is understood through the observed narrowing of this distribution during yield. Although the relaxation time distributions under deformation are highly protocol specific, in each case they may be described by a universal acceleration factor that depends only on the strain.
Modification of the aging dynamics of glassy polymers due to a temperature step
Mya Warren,Joerg Rottler
Physics , 2008, DOI: 10.1088/0953-8984/20/24/244131
Abstract: Molecular dynamics simulations are used to investigate the connection between thermal history and physical aging in polymer glasses, in particular the effects of a temperature square step. Measurements of two-time correlation functions show that a negative temperature step causes "rejuvenation" of the sample: the entire spectrum of relaxation times appears identical to a younger specimen that did not experience a temperature step. A positive temperature step, however, leads to significant changes in the relaxation times. At short times, the dynamics are accelerated (rejuvenation), whereas at long times the dynamics are slowed (over-aging). All findings are in excellent qualitative agreement with recent experiments. The two regimes can be explained by the competing contributions of dynamical heterogeneities and faster aging dynamics at higher temperatures. As a result of this competition, the transition between rejuvenation and over-aging depends on the length of the square step, with shorter steps causing more rejuvenation and longer steps causing more over-aging. Although the spectrum of relaxation times is greatly modified by a temperature step, the van Hove functions, which measure the distribution of particle displacements, exhibit complete superposition at times when the mean-squared displacements are equal.
Atomistic mechanism of physical ageing in glassy materials
Mya Warren,Joerg Rottler
Physics , 2009, DOI: 10.1209/0295-5075/88/58005
Abstract: Using molecular simulations, we identify microscopic relaxation events of individual particles in ageing structural glasses, and determine the full distribution of relaxation times. We find that the memory of the waiting time $t_w$ elapsed since the quench extends only up to the first relaxation event, while the distribution of all subsequent relaxation times (persistence times) follows a power law completely independent of history. Our results are in remarkable agreement with the well known phenomenological trap model of ageing. A continuous time random walk (CTRW) parametrized with the atomistic distributions captures the entire bulk diffusion behavior and explains the apparent scaling of the relaxation dynamics with $t_w$ during ageing, as well as observed deviations from perfect scaling.
Simulations of aging and plastic deformation in polymer glasses
Mya Warren,Joerg Rottler
Physics , 2007, DOI: 10.1103/PhysRevE.76.031802
Abstract: We study the effect of physical aging on the mechanical properties of a model polymer glass using molecular dynamics simulations. The creep compliance is determined simultaneously with the structural relaxation under a constant uniaxial load below yield at constant temperature. The model successfully captures universal features found experimentally in polymer glasses, including signatures of mechanical rejuvenation. We analyze microscopic relaxation timescales and show that they exhibit the same aging characteristics as the macroscopic creep compliance. In addition, our model indicates that the entire distribution of relaxation times scales identically with age. Despite large changes in mobility, we observe comparatively little structural change except for a weak logarithmic increase in the degree of short-range order that may be correlated to an observed decrease in aging with increasing load.
Gradient estimation in dendritic reinforcement learning
Mathieu Schiess, Robert Urbanczik, Walter Senn
The Journal of Mathematical Neuroscience , 2012, DOI: 10.1186/2190-8567-2-2
Abstract: Except for biologically detailed modeling studies, the overwhelming majority of works in mathematical neuroscience have treated neurons as point neurons, i.e., a linear aggregation of synaptic input followed by a nonlinearity in the generation of somatic action potentials was assumed to characterize a neuron. This disregards the fact that many neurons in the brain have complex dendritic arborization where synaptic inputs may be aggregated in highly nonlinear ways [1]. From an information processing perspective sticking with the minimal point neuron may nevertheless seem justified since networks of such simple neurons already display remarkable computational properties: assuming infinite precision and noiseless arithmetic a suitable network of spiking point neurons can simulate a universal Turing machine and, further, impressive information processing capabilities persist when one makes more realistic assumptions such as taking noise into account (see [2] and the references therein). Such generic observations are underscored by the detailed compartmental modeling of the computation performed in a hippocampal pyramidal cell [3]. There it was found that (in a rate coding framework) the input-output behavior of the complex cell is easily emulated by a simple two layer network of point neurons.If the computations of complex cells are readily emulated by relatively simple circuits of point neurons, the question arises why so many of the neurons in the brain are complex. Of course, the reason for this may be only loosely related to information processing proper, it might be that maintaining a complex cell is metabolically less costly than the maintenance of the equivalent network of point neurons. Here, we wish to explore a different hypothesis, namely that complex cells have crucial advantages with regard to learning. This hypothesis is motivated by the fact that many artificial intelligence algorithms for neural networks assume that synaptic plasticity is modulated by in
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