Acting without being in control: Exploring volition in Parkinson's disease with impulsive compulsive behaviours.

BACKGROUND: Several aspects of volitional control of action may be relevant in the pathophysiology of impulsive-compulsive behaviours (ICB) in Parkinson's disease (PD). We aimed to explore multiple aspects of action control, assessing reward-related behaviour, inhibition (externally and internally triggered) and sense of agency in PD patients, with and without ICB compared to healthy subjects. METHODS: Nineteen PD patients with ICB (PD-ICB), 19 PD without ICB (PD-no-ICB) and 19 healthy controls (HC) underwent a battery of tests including: Intentional Binding task which measures sense of agency; Stop Signal Reaction Time (SSRT) measuring capacity for reactive inhibition; the Marble task, assessing intentional inhibition; Balloon Analog Risk Task for reward sensitivity. RESULTS: One-way ANOVA showed significant main effect of group for action binding (p = 0.004, F = 6.27). Post hoc analysis revealed that PD-ICB had significantly stronger action binding than HC (p = 0.004), and PD-no-ICB (p = 0.04). There was no difference between PD-no-ICB and HC. SSRT did not differ between PD groups, whereas a significant difference between PD-no-ICB and HC was detected (p = 0.01). No other differences were found among groups in the other tasks. CONCLUSIONS: PD patients with ICB have abnormal performance on a psychophysical task assessing sense of agency, which might be related to a deficit in action representation at cognitive/experiential level. Yet, they have no deficit on tasks evaluating externally and internally triggered inhibitory control, or in reward-based decision-making. We conclude that impaired sense of agency may be a factor contributing to ICB in PD patients

The Chandra Dust Scattering Halo of Galactic Center transient Swift J174540.7-290015

We report the detection of a dust scattering halo around a recently discovered X-ray transient, Swift J174540.7-290015, which in early February of 2016 underwent one of the brightest outbursts (F_X ~ 5e-10 erg/cm^2/s) observed from a compact object in the Galactic Center field. We analyze four Chandra images that were taken as follow-up observations to Swift discoveries of new Galactic Center transients. After adjusting our spectral extraction for the effects of detector pileup, we construct a point spread function for each observation and compare it to the GC field before the outburst. We find residual surface brightness around Swift J174540.7-290015, which has a shape and temporal evolution consistent with the behavior expected from X-rays scattered by foreground dust. We examine the spectral properties of the source, which shows evidence that the object transitioned from a soft to hard spectral state as it faded below L_X ~ 1e36 erg/s. This behavior is consistent with the hypothesis that the object is a low mass X-ray binary in the Galactic Center.Comment: Accepted for publication in Ap

Interhemispheric communication during haptic self-perception

During the haptic exploration of a planar surface, slight resistances against the hand's movement are illusorily perceived as asperities (bumps) in the surface. If the surface being touched is one's own skin, an actual bump would also produce increased tactile pressure from the moving finger onto the skin. We investigated how kinaesthetic and tactile signals combine to produce haptic perceptions during self-touch. Participants performed two successive movements with the right hand. A haptic force-control robot applied resistances to both movements, and participants judged which movement was felt to contain the larger bump. An additional robot delivered simultaneous but task-irrelevant tactile stroking to the left forearm. These strokes contained either increased or decreased tactile pressure synchronized with the resistance-induced illusory bump encountered by the right hand. We found that the size of bumps perceived by the right hand was enhanced by an increase in left tactile pressure, but also by a decrease. Tactile event detection was thus transferred interhemispherically, but the sign of the tactile information was not respected. Randomizing (rather than blocking) the presentation order of left tactile stimuli abolished these interhemispheric enhancement effects. Thus, interhemispheric transfer during bimanual self-touch requires a stable model of temporally synchronized events, but does not require geometric consistency between hemispheric information, nor between tactile and kinaesthetic representations of a single common object

Uniform Approximation from Symbol Calculus on a Spherical Phase Space

We use symbol correspondence and quantum normal form theory to develop a more general method for finding uniform asymptotic approximations. We then apply this method to derive a result we announced in an earlier paper, namely, the uniform approximation of the $6j$-symbol in terms of the rotation matrices. The derivation is based on the Stratonovich-Weyl symbol correspondence between matrix operators and functions on a spherical phase space. The resulting approximation depends on a canonical, or area preserving, map between two pairs of intersecting level sets on the spherical phase space.Comment: 18 pages, 5 figure

Simultaneous Multi-band Radio & X-ray Observations of the Galactic Center Magnetar SGR 1745−-2900

We report on multi-frequency, wideband radio observations of the Galactic Center magnetar (SGR 1745$-$2900) with the Green Bank Telescope for $\sim$100 days immediately following its initial X-ray outburst in April 2013. We made multiple simultaneous observations at 1.5, 2.0, and 8.9 GHz, allowing us to examine the magnetar's flux evolution, radio spectrum, and interstellar medium parameters (such as the dispersion measure (DM), the scattering timescale and its index). During two epochs, we have simultaneous observations from the Chandra X-ray Observatory, which permitted the absolute alignment of the radio and X-ray profiles. As with the two other radio magnetars with published alignments, the radio profile lies within the broad peak of the X-ray profile, preceding the X-ray profile maximum by $\sim$0.2 rotations. We also find that the radio spectral index $\gamma$ is significantly negative between $\sim$2 and 9 GHz; during the final $\sim$30 days of our observations $\gamma \sim -1.4$, which is typical of canonical pulsars. The radio flux has not decreased during this outburst, whereas the long-term trends in the other radio magnetars show concomitant fading of the radio and X-ray fluxes. Finally, our wideband measurements of the DMs taken in adjacent frequency bands in tandem are stochastically inconsistent with one another. Based on recent theoretical predictions, we consider the possibility that the dispersion measure is frequency-dependent. Despite having several properties in common with the other radio magnetars, such as $L_{\textrm{X,qui}}/L_{\textrm{rot}} \lesssim 1$, an increase in the radio flux during the X-ray flux decay has not been observed thus far in other systems.Comment: 15 pages, 9 figures, 3 tables; accepted to Ap

The X-ray Point Source Population Hosted by Globular Clusters in the Elliptical Galaxy NGC 4261

Utilising archival Chandra X-ray Observatory data and Hubble Space Telescope globular cluster catalogues, we probe the time-domain properties of the low mass X-ray binary population in the elliptical galaxy NGC 4261. Of the 98 unique X-ray sources identified in this study, 62 sources are within the optical field of view and, of those, 33% are aligned with an optical cluster counterpart. We find twenty X-ray sources coincident with globular clusters; two are previously discovered ultra-luminous X-ray sources (ULXs) and eighteen are low mass X-ray binaries (GCLMXBs) with $L_X < 10^{39}$ erg s$^{-1}$. ULXs are a heterogeneous class of extremely bright X-ray binaries ($L_X > 10^{39}$ erg s$^{-1}$) and ULXs located in globular clusters (GCULXs) and may be indicators of black holes. Identifying these unusually X-ray bright sources and measuring their optical properties can provide valuable constraints on the progenitors of gravitational wave sources. We compare observations of these sources to the twenty previously-studied GCULXs from five other early-type galaxies, and find that GCULXs in NGC 4261 are of similar colour and luminosity and do not significantly deviate from the rest of the sample in terms of distance from the galaxy centre or X-ray luminosity. Both the GCULX and low mass X-ray binary (GCLMXB) populations of NGC 4261 show long term variability; the former may have implications for fast radio bursts originating in globular clusters and the latter will likely introduce additional scatter into the low mass end of GCLMXB X-ray luminosity functions.Comment: Accepted to MNRA

A tree-decomposed transfer matrix for computing exact Potts model partition functions for arbitrary graphs, with applications to planar graph colourings

Combining tree decomposition and transfer matrix techniques provides a very general algorithm for computing exact partition functions of statistical models defined on arbitrary graphs. The algorithm is particularly efficient in the case of planar graphs. We illustrate it by computing the Potts model partition functions and chromatic polynomials (the number of proper vertex colourings using Q colours) for large samples of random planar graphs with up to N=100 vertices. In the latter case, our algorithm yields a sub-exponential average running time of ~ exp(1.516 sqrt(N)), a substantial improvement over the exponential running time ~ exp(0.245 N) provided by the hitherto best known algorithm. We study the statistics of chromatic roots of random planar graphs in some detail, comparing the findings with results for finite pieces of a regular lattice.Comment: 5 pages, 3 figures. Version 2 has been substantially expanded. Version 3 shows that the worst-case running time is sub-exponential in the number of vertice

Asymptotes in SU(2) Recoupling Theory: Wigner Matrices, 3j3j Symbols, and Character Localization

In this paper we employ a novel technique combining the Euler Maclaurin formula with the saddle point approximation method to obtain the asymptotic behavior (in the limit of large representation index $J$) of generic Wigner matrix elements $D^{J}_{MM'}(g)$. We use this result to derive asymptotic formulae for the character $\chi^J(g)$ of an SU(2) group element and for Wigner's $3j$ symbol. Surprisingly, given that we perform five successive layers of approximations, the asymptotic formula we obtain for $\chi^J(g)$ is in fact exact. This result provides a non trivial example of a Duistermaat-Heckman like localization property for discrete sums.Comment: 36 pages, 3 figure

Semiclassical analysis of Wigner 3j3j-symbol

We analyze the asymptotics of the Wigner $3j$-symbol as a matrix element connecting eigenfunctions of a pair of integrable systems, obtained by lifting the problem of the addition of angular momenta into the space of Schwinger's oscillators. A novel element is the appearance of compact Lagrangian manifolds that are not tori, due to the fact that the observables defining the quantum states are noncommuting. These manifolds can be quantized by generalized Bohr-Sommerfeld rules and yield all the correct quantum numbers. The geometry of the classical angular momentum vectors emerges in a clear manner. Efficient methods for computing amplitude determinants in terms of Poisson brackets are developed and illustrated.Comment: 7 figure file

A strongly magnetized pulsar within grasp of the Milky Way's supermassive black hole

The center of our Galaxy hosts a supermassive black hole, Sagittarius (Sgr) A*. Young, massive stars within 0.5 pc of SgrA* are evidence of an episode of intense star formation near the black hole a few Myr ago, which might have left behind a young neutron star traveling deep into SgrA*'s gravitational potential. On 2013 April 25, a short X-ray burst was observed from the direction of the Galactic center. Thanks to a series of observations with the Chandra and the Swift satellites, we pinpoint the associated magnetar at an angular distance of 2.4+/-0.3 arcsec from SgrA*, and refine the source spin period and its derivative (P=3.7635537(2) s and \dot{P} = 6.61(4)x10^{-12} s/s), confirmed by quasi simultaneous radio observations performed with the Green Bank (GBT) and Parkes antennas, which also constrain a Dispersion Measure of DM=1750+/-50 pc cm^{-3}, the highest ever observed for a radio pulsar. We have found that this X-ray source is a young magnetar at ~0.07-2 pc from SgrA*. Simulations of its possible motion around SgrA* show that it is likely (~90% probability) in a bound orbit around the black hole. The radiation front produced by the past activity from the magnetar passing through the molecular clouds surrounding the Galactic center region, might be responsible for a large fraction of the light echoes observed in the Fe fluorescence features.Comment: ApJ Letters in pres