2,250 research outputs found
Spatial cognition during the active avoidance task: The role of the prefrontal cortex and preempting impairment following febrile status epilepticus
The active place avoidance task is a dynamic spatial cognition task that has been used to study spatial memory impairment in animal models of epilepsy in order to better understand how prolonged early-life seizures affect cognition. To determine whether the prefrontal cortex is necessary for this task, the performance of adult male rats (n = 3) was assessed before and after bilateral injections of muscimol or PBS in the medial prefrontal cortex (mPFC). Both muscimol and PBS impaired task performance, though only muscimol altered hippocampal oscillations in the theta and gamma ranges. Due to small sample size and potential confounds, these results do not strongly indicate the necessity of the mPFC in this task. However, muscimol had more profound effects on behavior and network activity than PBS, suggesting that with a bigger sample size the involvement of the mPFC could be demonstrated. In addition, the role of neuron-restrictive silencer factor (NRSF), a protein that is overexpressed after prolonged seizures, was investigated with regard to prolonged seizure-related cognitive deficits. Rats induced with febrile status epilepticus (FSE) and given intracerebral injections of neuron-restrictive silencer element (NRSE), which has been shown to decrease NRSF levels, performed as well as controls, measured in terms of shock zone entrances, shocks, and time spent opposite the shock zone. Untreated FSE rats were impaired in each of these measurements. These results provide strong evidence that NRSF overexpression mediates FSE-induced cognitive impairment
Anticipated Synchronization in a Biologically Plausible Model of Neuronal Motifs
Two identical autonomous dynamical systems coupled in a master-slave
configuration can exhibit anticipated synchronization (AS) if the slave also
receives a delayed negative self-feedback. Recently, AS was shown to occur in
systems of simplified neuron models, requiring the coupling of the neuronal
membrane potential with its delayed value. However, this coupling has no
obvious biological correlate. Here we propose a canonical neuronal microcircuit
with standard chemical synapses, where the delayed inhibition is provided by an
interneuron. In this biologically plausible scenario, a smooth transition from
delayed synchronization (DS) to AS typically occurs when the inhibitory
synaptic conductance is increased. The phenomenon is shown to be robust when
model parameters are varied within physiological range. Since the DS-AS
transition amounts to an inversion in the timing of the pre- and post-synaptic
spikes, our results could have a bearing on spike-timing-dependent-plasticity
models
Drifting instabilities of cavity solitons in vertical cavity surface-emitting lasers with frequency selective feedback
In this paper we study the formation and dynamics of self-propelled cavity
solitons (CSs) in a model for vertical cavity surface-emitting lasers (VCSELs)
subjected to external frequency selective feedback (FSF), and build their
bifurcation diagram for the case where carrier dynamics is eliminated. For low
pump currents, we find that they emerge from the modulational instability point
of the trivial solution, where traveling waves with a critical wavenumber are
formed. For large currents, the branch of self-propelled solitons merges with
the branch of resting solitons via a pitchfork bifurcation. We also show that a
feedback phase variation of 2\pi can transform a CS (whether resting or moving)
into a different one associated to an adjacent longitudinal external cavity
mode. Finally, we investigate the influence of the carrier dynamics, relevant
for VCSELs. We find and analyze qualitative changes in the stability properties
of resting CSs when increasing the carrier relaxation time. In addition to a
drifting instability of resting CSs, a new kind of instability appears for
certain ranges of carrier lifetime, leading to a swinging motion of the CS
center position. Furthermore, for carrier relaxation times typical of VCSELs
the system can display multistability of CSs.Comment: 11 pages, 12 figure
Dependence of carrier mobility on grain mosaic spread in 〈001〉-oriented Si films grown on polycrystalline substrates
We studied the dependence of carrier mobility on grain mosaic spread for 〈001〉-oriented, 200-to- 400-nm -thick Si thin films grown on polycrystalline metal substrates. The Hall mobility increased from 1% to 23% of that in bulk single-crystal Si with decreasing grain mosaic spread from 14° to 2°. For the same range of parameters, a model combining intragrain and grain boundary scattering yielded a decrease of the energy barrier height from 0.1 eV to less than 10-3 eV and an accompanying decrease of trap density from 6× 1011 cm-2 to less than 3× 1010 cm-2. These results demonstrate that, for polycrystalline Si films, improving the intergrain alignment is an effective and practical alternative to increasing the grain size to achieve enhanced mobility. © 2005 American Institute of Physics
Electron-phonon decoupling due to strong light-matter interactions
Phonon interactions in solid-state photonics systems cause intrinsic quantum
decoherence and often present the limiting factor in emerging quantum
technology. Due to recent developments in nanophotonics, exciton-cavity
structures with very strong light-matter coupling rates can be fabricated. We
show that in such structures, a new regime emerges, where the decoherence is
completely suppressed due to decoupling of the dominant phonon process. Using a
numerically exact tensor network approach, we perform calculations in this
non-perturbative, non-Markovian dynamical regime. Here, we identify a strategy
for reaching near-unity photon indistinguishability and also discover an
interesting phonon-dressing of the exciton-cavity polaritons in the high-Q
regime, leading to multiple phonon sidebands when the light-matter interaction
is sufficiently strong.Comment: Accepted for publication in Physical Review
Feasibility of diffusion and probabilistic white matter analysis in patients implanted with a deep brain stimulator.
Deep brain stimulation (DBS) for Parkinson\u27s disease (PD) is an established advanced therapy that produces therapeutic effects through high frequency stimulation. Although this therapeutic option leads to improved clinical outcomes, the mechanisms of the underlying efficacy of this treatment are not well understood. Therefore, investigation of DBS and its postoperative effects on brain architecture is of great interest. Diffusion weighted imaging (DWI) is an advanced imaging technique, which has the ability to estimate the structure of white matter fibers; however, clinical application of DWI after DBS implantation is challenging due to the strong susceptibility artifacts caused by implanted devices. This study aims to evaluate the feasibility of generating meaningful white matter reconstructions after DBS implantation; and to subsequently quantify the degree to which these tracts are affected by post-operative device-related artifacts. DWI was safely performed before and after implanting electrodes for DBS in 9 PD patients. Differences within each subject between pre- and post-implantation FA, MD, and RD values for 123 regions of interest (ROIs) were calculated. While differences were noted globally, they were larger in regions directly affected by the artifact. White matter tracts were generated from each ROI with probabilistic tractography, revealing significant differences in the reconstruction of several white matter structures after DBS. Tracts pertinent to PD, such as regions of the substantia nigra and nigrostriatal tracts, were largely unaffected. The aim of this study was to demonstrate the feasibility and clinical applicability of acquiring and processing DWI post-operatively in PD patients after DBS implantation. The presence of global differences provides an impetus for acquiring DWI shortly after implantation to establish a new baseline against which longitudinal changes in brain connectivity in DBS patients can be compared. Understanding that post-operative fiber tracking in patients is feasible on a clinically-relevant scale has significant implications for increasing our current understanding of the pathophysiology of movement disorders, and may provide insights into better defining the pathophysiology and therapeutic effects of DBS
Superoxide reductase from Giardia intestinalis: structural characterization of the first sor from a eukaryotic organism shows an iron centre that is highly sensitive to photoreduction
Superoxide reductase (SOR), which is commonly found in prokaryotic organisms, affords protection from oxidative stress by reducing the superoxide anion to hydrogen peroxide. The reaction is catalyzed at the iron centre, which is highly conserved among the prokaryotic SORs structurally characterized to date. Reported here is the first structure of an SOR from a eukaryotic organism, the protozoan parasite Giardia intestinalis (GiSOR), which was solved at 2.0 Ã… resolution. By collecting several diffraction data sets at 100 K from the same flash-cooled protein crystal using synchrotron X-ray radiation, photoreduction of the iron centre was observed. Reduction was monitored using an online UV-visible microspectrophotometer, following the decay of the 647 nm absorption band characteristic of the iron site in the glutamate-bound, oxidized state. Similarly to other 1Fe-SORs structurally characterized to date, the enzyme displays a tetrameric quaternary-structure arrangement. As a distinctive feature, the N-terminal loop of the protein, containing the characteristic EKHxP motif, revealed an unusually high flexibility regardless of the iron redox state. At variance with previous evidence collected by X-ray crystallography and Fourier transform infrared spectroscopy of prokaryotic SORs, iron reduction did not lead to dissociation of glutamate from the catalytic metal or other structural changes; however, the glutamate ligand underwent X-ray-induced chemical changes, revealing high sensitivity of the GiSOR active site to X-ray radiation damage
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