Muscle-specific variations in use-dependent crossed-facilitation of corticospinal pathways mediated by transcranial direct current (DC) stimulation

The tendency for contractions of muscles in the upper limb to give rise to increases in the excitability of corticospinal projections to the homologous muscles of the opposite limb is well known. Although the suppression of this tendency is integral to tasks of daily living, its exploitation may prove to be critical in the rehabilitation of acquired hemiplegias. Transcranial direct current (DC) stimulation induces changes in cortical excitability that outlast the period of application. We present evidence that changes in the reactivity of the corticospinal pathway induced by DC stimulation of the motor cortex interact systematically with those brought about by contraction of the muscles of the ipsilateral limb. During the application of flexion torques (up to 50% of maximum) applied at the left wrist, motor evoked potentials (MEPs) were evoked in the quiescent muscles of the right arm by magnetic stimulation of the left motor cortex (M1). The MEPs were obtained prior to and following 10 min of anodal, cathodal or sham DC stimulation of left M1. Cathodal stimulation counteracted increases in the crossed-facilitation of projections to the (right) wrist flexors that otherwise occurred as a result of repeated flexion contractions at the left wrist. In addition, cathodal stimulation markedly decreased the excitability of corticospinal projections to the wrist extensors of the right limb. Thus changes in corticospinal excitability induced by DC stimulation can be shaped (i.e. differentiated by muscle group) by focal contractions of muscles in the limb ipsilateral to the site of stimulation. (C) 2008 Elsevier Ireland Ltd. All rights reserved.

Visual feedback alters the variations in corticospinal excitability that arise from rhythmic movements of the opposite limb

Augmented visual feedback can have a profound bearing on the stability of bimanual coordination. Indeed, this has been used to render tractable the study of patterns of coordination that cannot otherwise be produced in a stable fashion. In previous investigations (Carson et al. 1999), we have shown that rhythmic movements, brought about by the contraction of muscles on one side of the body, lead to phase-locked changes in the excitability of homologous motor pathways of the opposite limb. The present study was conducted to assess whether these changes are influenced by the presence of visual feedback of the moving limb. Eight participants performed rhythmic flexion-extension movements of the left wrist to the beat of a metronome (1.5 Hz). In 50% of trials, visual feedback of wrist displacement was provided in relation to a target amplitude, defined by the mean movement amplitude generated during the immediately preceding no feedback trial. Motor potentials (MEPs) were evoked in the quiescent muscles of the right limb by magnetic stimulation of the left motor cortex. Consistent with our previous observations, MEP amplitudes were modulated during the movement cycle of the opposite limb. The extent of this modulation was, however, smaller in the presence of visual feedback of the moving limb (FCR omega(2) =0.41; ECR omega(2)=0.29) than in trials in which there was no visual feedback (FCR omega(2)=0.51; ECR omega(2)=0.48). In addition, the relationship between the level of FCR activation and the excitability of the homologous corticospinal pathway of the opposite limb was sensitive to the vision condition; the degree of correlation between the two variables was larger when there was no visual feedback of the moving limb. The results of the present study support the view that increases in the stability of bimanual coordination brought about by augmented feedback may be mediated by changes in the crossed modulation of excitability in homologous motor pathways.

A comprehensive comparison between generalized incidence calculus and Dempster-Shafer theory of evidence.

Dealing with uncertainty problems in intelligent systems has attracted a lot of attention in the AI community. Quite a few techniques have been proposed. Among them, the Dempster-Shafer theory of evidence (DS theory) has been widely appreciated. In DS theory, Dempster's combination rule plays a major role. However, it has been pointed out that the application domains of the rule are rather limited and the application of the theory sometimes gives unexpected results. We have previously explored the problem with Dempster's combination rule and proposed an alternative combination mechanism in generalized incidence calculus. In this paper we give a comprehensive comparison between generalized incidence calculus and the Dempster-Shafer theory of evidence. We first prove that these two theories have the same ability in representing evidence and combining DS-independent evidence. We then show that the new approach can deal with some dependent situations while Dempster's combination rule cannot. Various examples in the paper show the ways of using generalized incidence calculus in expert systems.

SuperWASP observations of long timescale photometric variations in cataclysmic variables

Aims: We investigated whether the predictions and results of Stanishev et al. (2002, A&A, 394, 625) concerning a possible relationship between eclipse depths in PX And and its retrograde disc precession phase, could be confirmed in long term observations made by SuperWASP. In addition, two further CVs (DQ Her and V795 Her) in the same SuperWASP data set were investigated to see whether evidence of superhump periods and disc precession periods were present and what other, if any, long term periods could be detected. Methods: Long term photometry of PX And, V795 Her and DQ Her was carried out and Lomb-Scargle periodogram analysis undertaken on the resulting light curves. For the two eclipsing CVs, PX And and DQ Her, we analysed the potential variations in the depth of the eclipse with cycle number. Results: The results of our period and eclipse analysis on PX And confirm that the negative superhump period is 0.1417 ± 0.0001d. We find no evidence of positive superhumps in our data suggesting that PX And may have been in a low state during our observations. We improve on existing estimates of the disc precession period and find it to be 4.43 ± 0.05d. Our results confirm the predictions of Stanishev et al. (2002). We find that DQ Her does not appear to show a similar variation for we find no evidence of negative superhumps or of a retrograde disc precession. We also find no evidence of positive superhumps or of a prograde disc precession and we attribute the lack of positive superhumps in DQ Her to be due to the high mass ratio of this CV. We do however find evidence for a modulation of the eclipse depth over a period of 100 days which may be linked with solar-type magnetic cycles which give rise to long term photometric variations. The periodogram analysis for V795 Her detected the likely positive superhump period 0.1165d, however, neither the 0.10826d orbital period nor the prograde 1.53d disc precession period were seen. Here though we have found a variation in the periodogram power function at the positive superhump period, over a period of at least 120 days.

A meta-analysis of latitudinal variations in life-history traits of roach, Rutilus rutilus, over its geographical range: linear or non-linear relationships?

1. We collated information from the literature on life history traits of the roach (a generalist freshwater fish), and analysed variation in absolute fecundity, von Bertalanffy parameters, and reproductive lifespan in relation to latitude, using both linear and non-linear regression models. We hypothesized that because most life history traits are dependent on growth rate, and growth rate is non-linearly related with temperature, it was likely that when analysed over the whole distribution range of roach, variation in key life history traits would show non-linear patterns with latitude.

Barrier height variations and interface properties of PtSi/Si structures

To study some of the interfacial properties of PtSi/Si diodes, Schottky structures were fabricated on (100) crystalline silicon substrates by conventional thermal evaporation of Pt on Si followed by annealing at different temperatures (from 400 degrees C to 700 degrees C) to form PtSi. The PtSi/n-Si diodes, all yielded Schottky barrier (SB) heights that are remarkably temperature dependent. The temperature range (20-290 K) over which the I-V characteristics were measured in the present study is broader with a much lower limit (20 K), than what is usually reported in literature. These variations in the barrier height are adequately interpreted by introducing spatial inhomogeneity into the barrier potential with a Gaussian distribution having a mean barrier of 0.76 eV and a standard deviation of 30 meV. Multi-frequency capacitance-voltage measurements suggest that the barrier is primarily controlled by the properties of the silicide-silicon interface. The forward C-V characteristics, in particular, show small peaks at low frequencies that can be ascribed to interface states rather than to a series resistance effect.

Orbital period variations of hot Jupiters caused by the Applegate effect

Several authors have shown that precise measurements of transit time variations of exoplanets can be sensitive to other planetary bodies, such as exo-moons. In addition, the transit timing variations of the exoplanets closest to their host stars can provide tests of tidal dissipation theory. These studies, however, have not considered the effect of the host star. There is a large body of observational evidence that eclipse times of binary stars can vary dramatically due to variations in the quadrupole moment of the stars driven by stellar activity. In this paper, we investigate and estimate the likely impact such variations have on the transit times of exoplanets. We find in several cases that such variations should be detectable. In particular, the estimated period changes for WASP-18b are of the same order as those expected for tidal dissipation, even for relatively low values of the tidal dissipation parameter. The transit time variations caused by the Applegate mechanism are also of the correct magnitude and occur on time-scales such that they may be confused with variations caused by light-travel time effects due to the presence of a Jupiter-like second planet. Finally, we suggest that transiting exoplanet systems may provide a clean route (compared to binaries) to constraining the type of dynamo operating in the host star.

Detection of epidermal growth factor receptor variations by partially denaturing HPLC

Background: Epidermal growth factor receptor gene (EGFR) variants may be useful markers for identifying responders to gefitinib and erlotinib, small-molecule tyrosine kinase inhibitors of EGFR; therefore, sensitive and cost-effective assays are needed to detect EGFR variants in routine clinical samples. We have developed a partially denaturing HPLC (pDHPLC) assay that is superior to direct sequencing with respect to detection limits, costs, and time requirements.

Variations in Apolipoprotein E Frequency With Age in a Pooled Analysis of a Large Group of Older People

Variation in the apolipoprotein E gene (APOE) has been reported to be associated with longevity in humans. The authors assessed the allelic distribution of APOE isoforms e2, e3, and e4 among 10,623 participants from 15 case-control and cohort studies of age-related macular degeneration (AMD) in populations of European ancestry (study dates ranged from 1990 to 2009). The authors included only the 10,623 control subjects from these studies who were classified as having no evidence of AMD, since variation within the APOE gene has previously been associated with AMD. In an analysis stratified by study center, gender, and smoking status, there was a decreasing frequency of the APOE e4 isoform with increasing age (?2 for trend = 14.9 (1 df); P = 0.0001), with a concomitant increase in the e3 isoform (?2 for trend = 11.3 (1 df); P = 0.001). The association with age was strongest in e4 homozygotes; the frequency of e4 homozygosity decreased from 2.7% for participants aged 60 years or less to 0.8% for those over age 85 years, while the proportion of participants with the e3/e4 genotype decreased from 26.8% to 17.5% across the same age range. Gender had no significant effect on the isoform frequencies. This study provides strong support for an association of the APOE gene with human longevity.