Categories and functional units: An infinite hierarchical model for brain activations

We present a model that describes the structure in the responses of different brain areas to a set of stimuli in terms of stimulus categories (clusters of stimuli) and functional units (clusters of voxels). We assume that voxels within a unit respond similarly to all stimuli from the same category, and design a nonparametric hierarchical model to capture inter-subject variability among the units. The model explicitly encodes the relationship between brain activations and fMRI time courses. A variational inference algorithm derived based on the model learns categories, units, and a set of unit-category activation probabilities from data. When applied to data from an fMRI study of object recognition, the method finds meaningful and consistent clusterings of stimuli into categories and voxels into units.National Science Foundation (U.S.) (Grant IIS/CRCNS 0904625)National Science Foundation (U.S.) (CAREER Grant 0642971)McGovern Institute for Brain Research at MIT (Neurotechnology Program Grant)National Institutes of Health (U.S.) (Grant NIBIB NAMIC U54-EB005149)National Institutes of Health (U.S.) (Grant NCRR NAC P41-RR13218

Search for patterns of functional specificity in the brain: A nonparametric hierarchical Bayesian model for group fMRI data

Functional MRI studies have uncovered a number of brain areas that demonstrate highly specific functional patterns. In the case of visual object recognition, small, focal regions have been characterized with selectivity for visual categories such as human faces. In this paper, we develop an algorithm that automatically learns patterns of functional specificity from fMRI data in a group of subjects. The method does not require spatial alignment of functional images from different subjects. The algorithm is based on a generative model that comprises two main layers. At the lower level, we express the functional brain response to each stimulus as a binary activation variable. At the next level, we define a prior over sets of activation variables in all subjects. We use a Hierarchical Dirichlet Process as the prior in order to learn the patterns of functional specificity shared across the group, which we call functional systems, and estimate the number of these systems. Inference based on our model enables automatic discovery and characterization of dominant and consistent functional systems. We apply the method to data from a visual fMRI study comprised of 69 distinct stimulus images. The discovered system activation profiles correspond to selectivity for a number of image categories such as faces, bodies, and scenes. Among systems found by our method, we identify new areas that are deactivated by face stimuli. In empirical comparisons with previously proposed exploratory methods, our results appear superior in capturing the structure in the space of visual categories of stimuli.McGovern Institute for Brain Research at MIT. Neurotechnology (MINT) ProgramNational Institutes of Health (U.S.) (Grant NIBIB NAMIC U54-EB005149)National Institutes of Health (U.S.) (Grant NCRR NAC P41-RR13218)National Eye Institute (Grant 13455)National Science Foundation (U.S.) (CAREER Grant 0642971)National Science Foundation (U.S.) (Grant IIS/CRCNS 0904625)Harvard University--MIT Division of Health Sciences and Technology (Catalyst Grant)American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowshi

The Circumstellar Environment of High Mass Protostellar Objects. III Evidence of Infall?

The results are presented of a molecular line survey to search for the spectral signature of infall towards 77 850 micron continuum sources believed to be candidate high mass protostellar objects. Up to six different transitions, HCO+ 1-0, 3-2 and 4-3, H2CO 2_12-1_11, N2H+ and H13CO+ 3-2, were observed towards each source. Towards the peak of the 850 micron emission, N2H+ was typically strong, with a peak antenna temperature of ~1.5K, with a typical linewidth of ~2km/s. The good agreement between the velocity and velocity width of the N2H+ and H13CO+ emission suggests that both species are tracing similar material in the sources. With respect to the velocity of the N2H+, there is a statistically significant excess of blue asymmetric line profiles in both the HCO+ 1-0 and H2CO transitions. This excess reaches levels similar to that seen towards samples of low mass protostars, and suggests that the material around these high mass sources is infalling. We identify 22 promising candidate infall sources which show at least one blue asymmetric line profile and no red asymmetric profiles. The infall velocity is estimated to be in the range of 0.1 km/s to 1 km/s with an implied mass accretion rate of between 2x10^{-4} Msol/yr and 10^{-3}Msol/yr.Comment: Accepted for publication in Astronomy and Astrophysics. Higher resolution versions of Figures 1 and 2 are available from http://www.jb.man.ac.uk/~gaf/Papers.htm

The Circumstellar Environments of High-Mass Protostellar Objects I: Submillimetre Continuum Emission

We present maps of the 850 micron and 450 micron continuum emission seen towards a sample of 68 high-mass protostellar candidates with luminosities ranging from 10^2.5 to 10^5 solar luminosity. Most of these candidate high-mass stars are in the earliest stages of evolution, and have not yet developed an ultra-compact HII region. We observe a variety of continuum emission morphologies, from compact symmetric sources through to multiple cores embedded in long filaments of emission. We find on average there is a 65% probability of an IRAS point-source having a companion detection at submillimetre wavelengths. The ratio of integrated flux to peak flux for our detections shows no strong dependence on distance, suggesting the emission we have observed is primarily from scale-free envelopes with power-law density structures. Assuming a near kinematic distance projection, the clumps we detect vary in mass from ~1 to over 1000 solar mass, with a mean clump mass of 330 solar mass, column density of 9x10^23 cm^-2 and diameter of ~0.6 pc. The high luminosity and low mass of the smallest clumps suggests they are accompanied by a minimal number of stellar companions, while the most massive clumps may be examples of young protogroups and protoclusters. We measure the spectral index of the dust emission (alpha) and the spectral index of the dust grain opacity (beta) towards each object, finding clumps with morphologies suggestive of strong temperature gradients, and of grain growth in their dense inner regions. We find a mean value for beta of 0.9, significantly smaller than observed towards UCHII regions.Comment: Accepted for publication in A&A (22 pages, 14 figures) Fixed missing pages in Tables 2 and

Epidemiologic study of myelodysplastic syndromes in a multiethnic, inner city cohort

Little is known about the epidemiology of MDS in minority populations. The IPSS and newly released IPSS-R are important clinical tools in prognostication of patients with MDS. Therefore, we conducted a retrospective epidemiological analysis of MDS in an ethnically diverse cohort of patients. Demographics, disease characteristics, and survival were determined in 161 patients seen at Montefiore Medical Center from 1997 to 2011. We observed that Hispanics presented at a younger age than blacks and whites (68 vs. 73.7 vs. 75.6 years); this difference was significant (p = 0.01). A trend towards greater prevalence of thrombocytopenia in Hispanics was observed, but this was not significant (p = 0.08). No other differences between the groups were observed. Overall median survival after diagnosis was the highest among Hispanics (8.6 years) followed by blacks (6.2 years) and Caucasians (3.7). Adjusted hazard ratios however did not show significant differences in risk of death between the groups. The IPSS-R showed slightly better discrimination when compared to the IPSS in this cohort (Somers Dxy 0.39 vs. 0.35, respectively) but observed survival more was more closely approximated by IPSS than by IPSS-R. Our study highlights the possibility of ethnic differences in the presentation of MDS and raises questions regarding which prognostic system is more predictive in this population

IRAS 05358+3543: Multiple outflows at the earliest stages of massive star formation

We present a high-angular-resolution molecular line and millimeter continuum study of the massive star formation site IRAS 05358+3543. The most remarkable feature is a highly collimated (collimation factor ~10) and massive (>10 M_sun) bipolar outflow of 1 pc length, which is part of a quadrupolar outflow system. The three observed molecular outflows forming the IRAS 05358+3543 outflow system resemble, in structure and collimation, those typical of low-mass star-forming regions. They might therefore, just like low-mass outflows, be explained by shock entrainment models of jets. We estimate a mass accretion rate of 10^{-4) M_sun/yr, sufficient to overcome the radiative pressure of the central object and to build up a massive star, lending further support to the hypothesis that massive star formation occurs similarly to low-mass star formation, only with higher accretion rates and energetics.Comment: 11 pages, 9 figures, accepted for Astronomy and Astrophysic

Long‐Term Variability and Tendencies in Middle Atmosphere Temperature and Zonal Wind From WACCM6 Simulations During 1850–2014

Long‐term variability of middle atmosphere temperature (T) and zonal wind (U) is investigated using a three‐member ensemble of historical simulations of NCAR's Whole Atmospheric Community Climate Model latest version 6 (WACCM6) for 1850–2014 (165 years). The model reproduces the climatological features of T and U. The contributions of Quasi Biennial Oscillation (QBO) at 10 and 30 hPa, solar cycle (SC), El Niño‐Southern Oscillation (ENSO), ozone depleting substances (ODS), carbon dioxide (CO2), and stratospheric sulfate aerosol (volcanic eruptions) to change in monthly zonal mean T and U are analyzed using multiple linear regression. The signal due to CO2 increase dominates as a predictor of the net multidecadal global annual mean temperature change at all levels in the middle atmosphere. Contributions from ODS also affect the net multidecadal global mean temperature trend in the stratosphere. Because of similarities in the time evolution of the emissions of CO2 and ODS, the analysis of existing model output cannot accurately separate the attributions of cooling to these two dominant forcing processes. On shorter time scales, solar flux variations are the largest source of variability in the mesosphere while volcanic eruptions are the largest in the stratosphere. In the stratosphere and mesosphere, both QBO and ENSO can significantly impact zonal mean temperature and zonal‐mean zonal wind depending on latitudes, but their impact on the multidecadal global mean temperature trend is very small

Long‐Term Variability and Tendencies in Migrating Diurnal Tide From WACCM6 Simulations During 1850–2014

Long‐term variability and tendencies in migrating diurnal tide (DW1) are investigated for the first time using a three‐member ensemble of historical simulations by NCAR's Whole Atmosphere Community Climate Model, latest Version 6 (WACCM6) for 1850–2014 (165 years). The model reproduces the climatological features of the tide in temperature (T), zonal wind (U), and meridional wind (V). The amplitudes peak in the upper mesosphere and lower thermosphere (above ~0.001 hPa) at the equator for T (~10 K) and over 20–30°N and S latitudes for U (~15 m/s) and V (~25 m/s). The contributions of solar cycle (SC), quasi biennial oscillation (QBO) at 10 and 30 hPa, El Niño–Southern Oscillation (ENSO), ozone depleting substances (ODS), carbon dioxide (CO2), and stratospheric sulfate aerosols (volcanic eruptions) to change in annual mean amplitudes are analyzed using multiple linear regression. The tidal amplitudes in three components show a long‐term increase in the upper stratosphere (0.95–10.7 hPa) and the upper mesosphere (0.0001–0.01 hPa), predominantly due to increasing CO2 with a smaller contribution from the trend in ENSO. Interestingly, the global mean tidal amplitude in T decreases sharply after 1950–1960 until 1995 and then increases in association with changes in ODSs. The seasonal differences in tidal responses to the above indices can be as large as the overall signals. All the responses are stronger in the upper mesosphere; however, there is also a pronounced negative response of temperature tide to ODSs over middle to high latitudes around the stratopause (~1 hPa) during all seasons

Study on Efficacy of Expired and Active Forms of Various Antibiotics on Saccharomyces cerevisiae

Antibiotics are among the most frequently prescribed medications in modern medicines. The cell protection strategies in the organisms, development of resistance in previously susceptible microbes, the inevitable progression of microbes exposed to antibiotics to develop resistance, were the nesisities that ensures the need for continual cycles of discovery and development of new antibiotics. A large variety of antibiotics are available in the drug market today, several others being added regularly in combat with various pathogens that cause disease in humans as well as in animals. Our present study focused to investigate the change in efficacy of commonly used antibiotics such as amoxicillin, ampicillin, sparfloxacin, cefixime. We have collected antibiotics with before and after their expiry dates. A simple eukaryotic model organism Saccharomyces cerevisiae is used to study the comparative understanding of this microbe with these different antibiotics. In our investigation we found that response of Sacchromyces cerevisiae towards different antibiotics varied in its intricacies. Fresh forms of antibiotics have significantly inhibiting the growth of Saccharomyces cerevisiae as compared to expired forms. The observations revealed that expired forms of antibiotics loose their efficacy drastically

High-Mass Proto-Stellar Candidates - I : The Sample and Initial Results

We describe a systematic program aimed at identifying and characterizing candidate high-mass proto-stellar objects (HMPOs). Our candidate sample consists of 69 objects selected by criteria based on those established by Ramesh & Sridharan (1997) using far-infrared, radio-continuum and molecular line data. Infrared-Astronomical-Satellite (IRAS) and Midcourse-Space-Experiment (MSX) data were used to study the larger scale environments of the candidate sources and to determine their total luminosities and dust temperatures. To derive the physical and chemical properties of our target regions, we observed continuum and spectral line radiation at millimeter and radio wavelengths. We imaged the free-free and dust continuum emission at wavelengths of 3.6 cm and 1.2 mm, respectively, searched for H2O and CH3OH maser emission and observed the CO 2-1 and several NH3 lines toward all sources in our sample. Other molecular tracers were observed in a subsample. The presented results indicate that a substantial fraction of our sample harbors HMPOs in a pre-UCHII region phase, the earliest known stage in the high-mass star formation process.Comment: 16 pages, 11 eps-figures. Astrophysical Journal, in pres