59 research outputs found
MEG event-related desynchronization and synchronization deficits during basic somatosensory processing in individuals with ADHD
<p>Abstract</p> <p>Background</p> <p>Attention-Deficit/Hyperactivity Disorder (ADHD) is a prevalent, complex disorder which is characterized by symptoms of inattention, hyperactivity, and impulsivity. Convergent evidence from neurobiological studies of ADHD identifies dysfunction in fronto-striatal-cerebellar circuitry as the source of behavioural deficits. Recent studies have shown that regions governing basic sensory processing, such as the somatosensory cortex, show abnormalities in those with ADHD suggesting that these processes may also be compromised.</p> <p>Methods</p> <p>We used event-related magnetoencephalography (MEG) to examine patterns of cortical rhythms in the primary (SI) and secondary (SII) somatosensory cortices in response to median nerve stimulation, in 9 adults with ADHD and 10 healthy controls. Stimuli were brief (0.2 ms) non-painful electrical pulses presented to the median nerve in two counterbalanced conditions: unpredictable and predictable stimulus presentation. We measured changes in strength, synchronicity, and frequency of cortical rhythms.</p> <p>Results</p> <p>Healthy comparison group showed strong event-related desynchrony and synchrony in SI and SII. By contrast, those with ADHD showed significantly weaker event-related desynchrony and event-related synchrony in the alpha (8–12 Hz) and beta (15–30 Hz) bands, respectively. This was most striking during random presentation of median nerve stimulation. Adults with ADHD showed significantly shorter duration of beta rebound in both SI and SII except for when the onset of the stimulus event could be predicted. In this case, the rhythmicity of SI (but not SII) in the ADHD group did not differ from that of controls.</p> <p>Conclusion</p> <p>Our findings suggest that somatosensory processing is altered in individuals with ADHD. MEG constitutes a promising approach to profiling patterns of neural activity during the processing of sensory input (e.g., detection of a tactile stimulus, stimulus predictability) and facilitating our understanding of how basic sensory processing may underlie and/or be influenced by more complex neural networks involved in higher order processing.</p
A Deep XMM-Newton Survey of M33: Point Source Catalog, Source Detection and Characterization of Overlapping Fields
We have obtained a deep 8-field XMM-Newton mosaic of M33 covering the galaxy
out to the D isophote and beyond to a limiting 0.2--4.5 keV unabsorbed
flux of 510 erg cm s (L410
erg s at the distance of M33). These data allow complete coverage of the
galaxy with high sensitivity to soft sources such as diffuse hot gas and
supernova remnants. Here we describe the methods we used to identify and
characterize 1296 point sources in the 8 fields. We compare our resulting
source catalog to the literature, note variable sources, construct hardness
ratios, classify soft sources, analyze the source density profile, and measure
the X-ray luminosity function. As a result of the large effective area of
XMM-Newton below 1 keV, the survey contains many new soft X-ray sources. The
radial source density profile and X-ray luminosity function for the sources
suggests that only 15% of the 391 bright sources with
L3.610 erg s are likely to be associated with M33,
and more than a third of these are known supernova remnants. The log(N)--log(S)
distribution, when corrected for background contamination, is a relatively flat
power-law with a differential index of 1.5, which suggests many of the other
M33 sources may be high-mass X-ray binaries. Finally, we note the discovery of
an interesting new transient X-ray source, which we are unable to classify.Comment: 26 pages, 6 tables, 13 figures, accepted for publication in ApJ
SXP214, an X-ray Pulsar in the Small Magellanic Cloud, Crossing the Circumstellar Disk of the Companion
Located in the Small Magellanic Cloud (SMC), SXP214 is an X-ray pulsar in a
high mass X-ray binary system with a Be-star companion. A recent survey of the
SMC under a Chandra X-ray Visionary program found the source in a transition
when the X-ray flux was on a steady rise. The Lomb-Scargle periodogram revealed
a pulse period of 211.49 +/- 0.42 s, which is significantly (>5sigma) shorter
than the previous measurements with XMM-Newton and RXTE. This implies that the
system has gone through sudden spin-up episodes recently. The pulse profile
shows a sharp eclipse-like feature with a modulation amplitude of >95%. The
linear rise of the observed X-ray luminosity from <~2x to 7x10^35 erg s^-1 is
correlated with steady softening of the X-ray spectrum, which can be described
by the changes in the local absorption from N_H ~ 10^24 to <~10^20 cm^-2 for an
absorbed power-law model. The soft X-ray emission below 2 keV was absent in the
early part of the observation when only the pulsating hard X-ray component was
observed, whereas at later times both soft and hard X-ray components were
observed pulsating. A likely explanation is that the neutron star was initially
hidden in the circumstellar disk of the companion, and later came out of the
disk with the accreted material that continued fueling the observed pulsation.Comment: 8 pages, 4 figures, 1 table, accepted for publication in Ap
Chandra ACIS Survey of M33 (ChASeM33): X-ray Imaging Spectroscopy of M33SNR21, the Brightest X-ray Supernova Remnant in M33
We present and interpret new X-ray data for M33SNR21, the brightest X-ray
supernova remnant (SNR) in M33. The SNR is in seen projection against (and
appears to be interacting with) the bright HII region NGC592. Data for this
source were obtained as part of the Chandra ACIS Survey of M33 (ChASeM33) Very
Large Project. The nearly on-axis Chandra data resolve the SNR into a ~5"
diameter (20 pc at our assumed M33 distance of 817+/-58 kpc) slightly
elliptical shell. The shell is brighter in the east, which suggests that it is
encountering higher density material in that direction. The optical emission is
coextensive with the X-ray shell in the north, but extends well beyond the
X-ray rim in the southwest. Modeling the X-ray spectrum with an absorbed sedov
model yields a shock temperature of 0.46(+0.01,-0.02) keV, an ionization
timescale of n_e t = cm s, and
half-solar abundances (0.45 (+0.12, -0.09)). Assuming Sedov dynamics gives an
average preshock H density of 1.7 +/- 0.3 cm. The dynamical age estimate
is 6500 +/- 600 yr, while the best fit value and derived gives
8200 +/- 1700 yr; the weighted mean of the age estimates is 7600 +/- 600 yr. We
estimate an X-ray luminosity (0.25-4.5 keV) of (1.2 +/- 0.2) times
ergs s (absorbed), and (1.7 +/- 0.3) times ergs s
(unabsorbed), in good agreement with the recent XMM-Newton determination. No
significant excess hard emission was detected; the luminosity ergs s (2-8 keV) for any hard point source.Comment: 27 pages, 6 figures (3 color). ApJ (in press
FUV and X-ray Observations of the Reverse Shock in the SMC SNR 1E 0102.2-7219
We present FUSE and XMM-Newton data for the reverse shock of the O-rich SNR
1E0102.2-7219 in the SMC. The FUSE observations cover three regions with
significantly different optical [O III] intensities, all associated with the
relatively bright part of the X-ray ring. Emission lines of O VI 1032, 1038 are
clearly detected in the FUSE spectra. By combining this O VI doublet emission
with the O VII triplet and O VIII Lyalpha fluxes from the XMM-Newton spectra
and assuming a non-equilibrium ionization model with a single ionization
timescale for the spectra, we are able to find a narrow range of temperatures
and ionization timescales that are consistent with the respective line ratios.
However, if we assume a plane-parallel shock model with a distribution of
ionization timescales, the O VI emission appears to be inconsistent with O VII
and O VIII in X-rays. We also analyze the total XMM-Newton EPIC-MOS 1/2 spectra
for the three regions. The X-ray spectra are dominated by strong emission lines
of O, Ne, and Mg, however, we detect an emission component that accounts for 14
- 25% of the flux and can be attributed to shocked ISM. We find that there is
no consistent set of values for the temperature and ionization timescale which
can explain the observed line ratios for O, Ne, and Mg. This would be
consistent with a structured distribution of the ejecta as the O, Ne, Mg would
have interacted with the reverse shock at different times.Comment: 28 pages, 5 figues, Fig. 1 as JPEG. To be published in ApJ (01 May
2006, v. 642, 1 issue
Chandra ACIS Survey of M33 (ChASeM33): A First Look
We present an overview of the Chandra ACIS Survey of M33 (ChASeM33): A Deep
Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the
galaxy out to R \approx 18\arcmin (\approx 4 kpc). These data provide the
most intensive, high spatial resolution assessment of the X-ray source
populations available for the confused inner regions of M33. Mosaic images of
the ChASeM33 observations show several hundred individual X-ray sources as well
as soft diffuse emission from the hot interstellar medium. Bright, extended
emission surrounds the nucleus and is also seen from the giant \hii regions NGC
604 and IC 131. Fainter extended emission and numerous individual sources
appear to trace the inner spiral structure. The initial source catalog, arising
from ~2/3 of the expected survey data, includes 394 sources significant
at the confidence level or greater, down to a limiting luminosity
(absorbed) of 1.6\ergs{35} (0.35 -- 8.0 keV). The hardness ratios of the
sources separate those with soft, thermal spectra such as supernova remnants
from those with hard, non-thermal spectra such as X-ray binaries and background
active galactic nuclei. Emission extended beyond the Chandra point spread
function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33
sources against previous catalogs of X-ray sources in M33 results in matches
for the vast majority of the brighter sources and shows 28 ChASeM33 sources
within 10\arcsec of supernova remnants identified by prior optical and radio
searches. This brings the total number of such associations to 31 out of 100
known supernova remnants in M33.Comment: accepted for publication ApJS, full resolution images and complete
tables available at http://hea-www.harvard.edu/vlp_m33_public
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