115 research outputs found
Loss of intranetwork and internetwork resting state functional connections with Alzheimer\u27s disease progression
Alzheimer\u27s disease (AD) is the most common cause of dementia. Much is known concerning AD pathophysiology but our understanding of the disease at the systems level remains incomplete. Previous AD research has used resting-state functional connectivity magnetic resonance imaging (rs-fcMRI) to assess the integrity of functional networks within the brain. Most studies have focused on the default-mode network (DMN), a primary locus of AD pathology. However, other brain regions are inevitably affected with disease progression. We studied rs-fcMRI in five functionally defined brain networks within a large cohort of human participants of either gender (n = 510) that ranged in AD severity from unaffected [clinical dementia rating (CDR) 0] to very mild (CDR 0.5) to mild (CDR 1). We observed loss of correlations within not only the DMN but other networks at CDR 0.5. Within the salience network (SAL), increases were seen between CDR 0 and CDR 0.5. However, at CDR 1, all networks, including SAL, exhibited reduced correlations. Specific networks were preferentially affected at certain CDR stages. In addition, cross-network relations were consistently lost with increasing AD severity. Our results demonstrate that AD is associated with widespread loss of both intranetwork and internetwork correlations. These results provide insight into AD pathophysiology and reinforce an integrative view of the brain\u27s functional organization
The ultraviolet visibility and quantitative morphology of galactic disks at low and high redshift
We used ultraviolet (200 nm) images of the local spiral galaxies M33, M51,
M81, M100, M101 to compute morphological parameters of galactic disks at this
wavelength : half-light radius , surface brightness distributions,
asymmetries () and concentrations (). The visibility and the evolution
of the morphological parameters are studied as a function of the redshift. The
main results are : local spiral galaxies would be hardly observed and
classified if projected at high redshifts (z 1) unless a strong
luminosity evolution is assumed. Consequently, the non-detection of large
galactic disks cannot be used without caution as a constraint on the evolution
of galatic disks. Spiral galaxies observed in ultraviolet appear more irregular
since the contribution from the young stellar population becomes predominent.
When these galaxies are put in a (log vs. log ) diagram, they move to
the irregul ar sector defined at visible wavelengths. Moreover, the log
parameter is degenerate and cannot be used for an efficient classification of
morphological ultraviolet types. The analysis of high redshift galaxies cannot
be carried out in a reliable way so far and a multi-wavelength approach is
required if one does not want to misinterpret the data.Comment: 12 pages, accepted for publication in A&A on 15 January 200
The Evolution of 3CR Radio Galaxies from z=1
We present the results of a comprehensive re-analysis of the images of a
virtually complete sample of 28 powerful 3CR radio galaxies with redshifts
0.6<z<1.8 from the HST archive. Using a two-dimensional modelling technique we
have derived scalelengths and absolute magnitudes for a total of 16 3CR
galaxies with a median redshift of z=0.8. Our results confirm the basic
conclusions of Best, Longair & R\"{o}ttgering (1997, 1998) in that we also find
z=1 3CR galaxies to be massive, well-evolved ellipticals, whose infrared
emission is dominated by starlight. However, we in fact find that the
scalelength distribution of 3CR galaxies at z \simeq 1 is completely
indistinguishable from that derived for their low-redshift counterparts from
our own recently-completed HST study of AGN hosts at z \simeq 0.2. There is
thus no evidence that 3CR radio galaxies at z \simeq 1 are dynamically
different from 3CR galaxies at low redshift. Moreover, for a 10-object
sub-sample we have determined the galaxy parameters with sufficient accuracy to
demonstrate, for the first time, that the z \simeq 1 3CR galaxies follow a
Kormendy relation which is indistinguishable from that displayed by
low-redshift ellipticals if one allows for purely passive evolution. The
implied rather modest level of passive evolution since z \simeq 1 is consistent
with that predicted from spectrophotometric models provided one assumes a high
formation redshift (z \ge 4) within a low-density Universe. We conclude that
there is no convincing evidence for significant dynamical evolution among 3CR
galaxies in the redshift interval 0<z<1, and that simple passive evolution
remains an acceptable interpretation of the K-z relation for powerful radio
galaxies.Comment: 10 pages, 5 figures, minor changes, accepted for publication in MNRA
Photometric Properties of Galaxy Population in the Cluster EIS 0048-2942 at z~0.64
~Deep photometric data in the V-, R-, I-, z- and K-bands for the cluster of
galaxies EIS 0048-2942 are used to investigate the properties of the galaxy
populations at z~0.64 in a field of 2.5x2.5 Mpc^2. The sample of candidate
cluster members (N = 171) is selected by the photometric redshift technique and
is complete up to I=22.5. Galaxies were classified as spheroids and disks
according to the shape of the light profile in the I-band, as parametrized by
the Sersic index. In both optical and NIR, spheroids define a sharp
colour-magnitude sequence, whose slope and zero points are consistent with a
high formation redshift (z_f > 2). The disk population occupies a different
region in the colour-magnitude diagram, having bluer colours with respect to
the red sequence. Interestingly, we find some level of mixing between the
properties of the two classes: some disks lie on the colour-magnitude sequence
or are redder, while some spheroids turn out to be bluer. The spatial
distribution of cluster galaxies show a clumpy structure, with a main
over-density of radius ~0.5 Mpc, and at least two other clumps distant ~1 Mpc
from the center. The various sub-structures are mostly populated by the red
galaxies, while the blue population has an almost uniform distribution. The
fraction of blue galaxies in EIS 0048-2942 is f_B=0.11 +/-0.07. This is much
lower than what expected on the basis of the Butcher-Oemler effect at lower
redshifts.Comment: 22 pages, 12 figures. A&A in pres
An HST Morphological Survey of Faint EROs
We present the results from a survey for Extremely Red Objects (EROs) in
deep, high resolution optical images taken from the Hubble Space Telescope
(HST) Medium Deep Survey. We have surveyed 35 deep F814W HST/WFPC2 fields in
the near-infrared to a typical depth of K~20. From a total area of 206 arcmin^2
and to a limit of K=20.0 we identify 224 EROs ((1.14+/-0.08) arcmin^-2) with
(I_{814}-K)=>4.0 and 83 ((0.41+/-0.05) arcmin^-2) with (I_{814}-K)=>5.0. We
find that the slope of the number counts of the (I_{814}-K)=>4.0 EROs flattens
beyond K~19, in line with results from previous surveys, and the typical
colours of the EROs become redder beyond the break magnitude. We
morphologically classify our ERO sample using visual and quantitative schemes
and find that 35% of our sample exhibit clear disk components, 15% are
disturbed or irregular, a further 30% are either spheroidal or compact and the
remaining 20% are unclassifiable. Using a quantitative measure of morphology,
we find that the ERO morphological distribution evolves across the break in
their counts, such that low concentration (disk-like) galaxies decline. We
relate the morphological and colour information for our EROs and conclude that
those EROs morphologically classified as bulges do indeed possess SEDs
consistent with passive stellar populations; while EROs with dusty star-forming
SEDs are mostly associated with disk-like and peculiar galaxies. However, ~30%
of disk EROs reside in the passive region of I/J/K colour-colour space. These
could be either genuinely passive systems, lower redshift contaminants to the
high-z ERO population, or systems with composite star-forming and passive SEDs.Comment: 20 pages, 14 figures. MNRAS submitted, revised in response to
referee's comment
An Observational Test for the Anthropic Origin of the Cosmological Constant
The existence of multiple regions of space beyond the observable Universe
(within the so-called "multiverse") where the vacuum energy density takes
different values, has been postulated as an explanation for the low non-zero
value observed for it in our Universe. It is often argued that our existence
pre-selects regions where the cosmological constant is sufficiently small to
allow galaxies like the Milky Way to form and intelligent life to emerge. Here
we propose a simple empirical test for this anthropic argument within the
boundaries of the observable Universe. We make use of the fact that dwarf
galaxies formed in our Universe at redshifts as high as z~10 when the mean
matter density was larger by a factor of ~10^3 than today. Existing technology
enables to check whether planets form in nearby dwarf galaxies and globular
clusters by searching for microlensing or transit events of background stars.
The oldest of these nearby systems may have formed at z~10. If planets are as
common per stellar mass in these descendents as they are in the Milky Way
galaxy, then the anthropic argument would be weakened considerably since
planets could have formed in our Universe even if the cosmological constant was
three orders of magnitude larger than observed. For a flat probability
distribution, this would imply that the probability for us to reside in a
region where the cosmological constant obtains its observed value is lower than
\~10^{-3}. A precise version of the anthropic argument could then be ruled-out
at a confidence level of ~99.9%, which constitutes a satisfactory measure of a
good experimental test.Comment: JCAP, in pres
Respiratory syncytial virus infection induces higher Toll-like receptor-3 expression and TNF-Ξ± production than human metapneumovirus infection
published_or_final_versio
Fear expression is suppressed by tyrosine administration
Animal studies have demonstrated that catecholamines regulate several aspects of fear conditioning. In humans, however, pharmacological manipulations of the catecholaminergic system have been scarce, and their primary focus has been to interfering with catecholaminergic activity after fear acquisition or expression had taken place, using L-Dopa, primarily, as catecholaminergic precursor. Here, we sought to determine if putative increases in presynaptic dopamine and norepinephrine by tyrosine administered before conditioning could affect fear expression. Electrodermal activity (EDA) of 46 healthy participants (24 placebo, 22 tyrosine) was measured in a fear instructed task. Results showed that tyrosine abolished fear expression compared to placebo. Importantly, tyrosine did not affect EDA responses to the aversive stimulus (UCS) or alter participants' mood. Therefore, the effect of tyrosine on fear expression cannot be attributed to these factors. Taken together, these findings provide evidence that the catecholaminergic system influences fear expression in humans
A dopaminergic switch for fear to safety transitions
Overcoming aversive emotional memories requires neural systems that detect when fear responses are no longer appropriate. The midbrain ventral tegmental area (VTA) dopamine system has been implicated in reward and more broadly in signalling when a better than expected outcome has occurred. This suggests that it may be important in guiding fear to safety transitions. We report that when an expected aversive outcome does not occur, activity in midbrain dopamine neurons is necessary to extinguish behavioral fear responses and engage molecular signalling events in extinction learning circuits. Furthermore, a specific dopamine projection to the nucleus accumbens medial shell is partially responsible for this effect. By contrast, a separate dopamine projection to the medial prefrontal cortex opposes extinction learning. This demonstrates a novel function for the canonical VTA-dopamine reward system and reveals opposing behavioural roles for different dopamine neuron projections in fear extinction learning
A Panchromatic Catalog of Early-Type Galaxies at Intermediate Redshift in the Hubble Space Telescope Wide Field Camera 3 Early Release Science Field
In the first of a series of forthcoming publications, we present a
panchromatic catalog of 102 visually-selected early-type galaxies (ETGs) from
observations in the Early Release Science (ERS) program with the Wide Field
Camera 3 (WFC3) on the Hubble Space Telescope (HST) of the Great Observatories
Origins Deep Survey-South (GOODS-S) field. Our ETGs span a large redshift
range, 0.35 < z < 1.5, with each redshift spectroscopically-confirmed by
previous published surveys of the ERS field. We combine our measured WFC3 ERS
and ACS GOODS-S photometry to gain continuous sensitivity from the rest-frame
far-UV to near-IR emission for each ETG. The superior spatial resolution of the
HST over this panchromatic baseline allows us to classify the ETGs by their
small-scale internal structures, as well as their local environment. By fitting
stellar population spectral templates to the broad-band photometry of the ETGs,
we determine that the average masses of the ETGs are comparable to the
characteristic stellar mass of massive galaxies, 11< log(M [Solar]) < 12.
By transforming the observed photometry into the GALEX FUV and NUV, Johnson
V, and SDSS g' and r' bandpasses we identify a noteworthy diversity in the
rest-frame UV-optical colors and find the mean rest-frame (FUV-V)=3.5 and
(NUV-V)=3.3, with 1 standard deviations approximately equal to 1.0. The
blue rest-frame UV-optical colors observed for most of the ETGs are evidence
for star-formation during the preceding gigayear, but no systems exhibit
UV-optical photometry consistent with major recent (<~50 Myr) starbursts.
Future publications which address the diversity of stellar populations likely
to be present in these ETGs, and the potential mechanisms by which recent
star-formation episodes are activated, are discussed.Comment: accepted to the Astrophysical Journal Supplement Serie
- β¦