Are short-term variations in solar oscillation frequencies the signature of a second solar dynamo?

In addition to the well-known 11-year solar cycle, the Sun's magnetic activity also shows significant variation on shorter time scales, e.g. between one and two years. We observe a quasi-biennial (2-year) signal in the solar p-mode oscillation frequencies, which are sensitive probes of the solar interior. The signal is visible in Sun-as-a-star data observed by different instruments and here we describe the results obtained using BiSON, GOLF, and VIRGO data. Our results imply that the 2-year signal is susceptible to the influence of the main 11-year solar cycle. However, the source of the signal appears to be separate from that of the 11-year cycle. We speculate as to whether it might be the signature of a second dynamo, located in the region of near-surface rotational shear.Comment: 6 pages, 2 figures, proceedings for SOHO-24/GONG 2010 conference, to be published in JPC

Assessment of Translocator Protein Density, as Marker of Neuroinflammation, in Major Depressive Disorder: A Pilot, Multicenter, Comparative, Controlled, Brain PET Study (INFLADEP Study)

Background: Major depressive disorder (MDD) is a serious public health problem with high lifetime prevalence (4.4–20%) in the general population. The monoamine hypothesis is the most widespread etiological theory of MDD. Also, recent scientific data has emphasized the importance of immuno-inflammatory pathways in the pathophysiology of MDD. The lack of data on the magnitude of brain neuroinflammation in MDD is the main limitation of this inflammatory hypothesis. Our team has previously demonstrated the relevance of [18F] DPA-714 as a neuroinflammation biomarker in humans. We formulated the following hypotheses for the current study: (i) Neuroinflammation in MDD can be measured by [18F] DPA-714; (ii) its levels are associated with clinical severity; (iii) it is accompanied by anatomical and functional alterations within the frontal-subcortical circuits; (iv) it is a marker of treatment resistance.Methods: Depressed patients will be recruited throughout 4 centers (Bordeaux, Montpellier, Tours, and Toulouse) of the French network from 13 expert centers for resistant depression. The patient population will be divided into 3 groups: (i) experimental group—patients with current MDD (n = 20), (ii) remitted depressed group—patients in remission but still being treated (n = 20); and, (iii) control group without any history of MDD (n = 20). The primary objective will be to compare PET data (i.e., distribution pattern of neuroinflammation) between the currently depressed group and the control group. Secondary objectives will be to: (i) compare neuroinflammation across groups (currently depressed group vs. remitted depressed group vs. control group); (ii) correlate neuroinflammation with clinical severity across groups; (iii) correlate neuroinflammation with MRI parameters for structural and functional integrity across groups; (iv) correlate neuroinflammation and peripheral markers of inflammation across groups.Discussion: This study will assess the effects of antidepressants on neuroinflammation as well as its role in the treatment response. It will contribute to clarify the putative relationships between neuroinflammation quantified by brain neuroimaging techniques and peripheral markers of inflammation. Lastly, it is expected to open innovative and promising therapeutic perspectives based on anti-inflammatory strategies for the management of treatment-resistant forms of MDD commonly seen in clinical practice.Clinical trial registration (reference: NCT03314155): https://www.clinicaltrials.gov/ct2/show/NCT03314155?term=neuroinflammation&cond=depression&cntry=FR&rank=

Astrophotometric variability of CFHT-LS Deep 2 QSOs

International audienceContext. The current conventional realization of the ICRS (International Celestial Reference System) is, in the radio wavelength, the International Celestial Reference Frame 2 (ICRF2). The individual positions of the defining sources have been found to have accuracies better than 1 milliarcsecond (mas). In 2012, the European astrometric satellite Gaia will be launched. This mission will provide an astrometric catalog of an estimated number of 500 000 QSOs. The uncertainty in the coordinates is anticipated to be 200 microarcsecond (muas) for the magnitude = 20. If this were achieved, the ICRF and the Gaia related reference frame could be related with a muas accuracy. Aims: The goal of this work is both to measure the photometric variability of a set of quasars in a given field, and search wether this variability can be related to an astrometric instability characterized by a motion of the quasar photocenter. If this correlation existed for some given QSO, then it would be inadequate to materialize the Gaia extragalactic reference frame at the level of confidence required, i.e. the sub-milliarcsecond one. This should be an important result in the scope of the Gaia mission. Methods: We use QSO CCD images obtained over 4.5 years with the Canada France Hawaï Telescope (CFHT) in the framework of the CFHT-Legacy Survey (CFHT-LS). The pictures were analysed with both the SExtractor software and customised codes to perform a photometric calibration together with an astrometric one. A total of 41 QSOs in the Deep 2 field were analysed. Magnitude variations during more than 50 months are given at three different bandwiths G, R, and I. Among the set above, 5 quasars were chosen to test the ties between the postion of their centroid and their magnitude variations. For one of these 5 QSOs, the proximity of a neighbouring star allows the comparison between the PSFs. Results: We clearly show significant photometric variations reaching sometimes more than one magnitude, for a good proportion of the 41 quasars in our sample. We show that these variations often occur within a few months, and that the correlation between the photometric curves in the three bands, G, R and I is obvious. As a second important result, we show that with a reasonably high probability, photometric variations for one quasar in our sample are accompagnied by substantial modification of its PSF

Insight on AV-45 binding in white and grey matter from histogram analysis: a study on early Alzheimer's disease patients and healthy subjects.

International audiencePURPOSE: AV-45 amyloid biomarker is known to show uptake in white matter in patients with Alzheimer's disease (AD), but also in the healthy population. This binding, thought to be of a non-specific lipophilic nature, has not yet been investigated. The aim of this study was to determine the differential pattern of AV-45 binding in white matter in healthy and pathological populations. METHODS: We recruited 24 patients presenting with AD at an early stage and 17 matched, healthy subjects. We used an optimized positron emission tomography-magnetic resonance imaging (PET-MRI) registration method and an approach based on an intensity histogram using several indices. We compared the results of the intensity histogram analyses with a more canonical approach based on target-to-cerebellum Standard Uptake Value (SUVr) in white and grey matter using MANOVA and discriminant analyses. A cluster analysis on white and grey matter histograms was also performed. RESULTS: White matter histogram analysis revealed significant differences between AD and healthy subjects, which were not revealed by SUVr analysis. However, white matter histograms were not decisive to discriminate groups, and indices based on grey matter only showed better discriminative power than SUVr. The cluster analysis divided our sample into two clusters, showing different uptakes in grey, but also in white matter. CONCLUSION: These results demonstrate that AV-45 binding in white matter conveys subtle information not detectable using the SUVr approach. Although it is not more efficient than standard SUVr in discriminating AD patients from healthy subjects, this information could reveal white matter modifications

Alzheimers Res Ther

BACKGROUND: Vitamin D deficiency is associated with an increased risk of Alzheimer's disease and increased beta-amyloid (Abeta) in animals. Hence we sought to investigate the relationship between plasma 25-hydroxyvitamin D (25(OH)D) and cerebral Abeta in older adults with subjective memory complaints. METHODS: This is a secondary analysis of the Multidomain Alzheimer Preventive Trial. Participants were 178 dementia-free individuals aged 70 years or older with data on plasma 25(OH)D and cerebral Abeta load assessed by [(18)F]-florbetapir positron emission tomography. Plasma 25(OH)D was measured at study baseline using a commercially available electro-chemiluminescence competitive binding assay. Standard uptake value ratios (SUVRs) were generated using the cerebellum as a reference. Brain regions assessed included the cortex, anterior cingulate, anterior putamen, caudate, hippocampus, medial orbitofrontal cortex, occipital cortex, parietal cortex, pons, posterior cingulate, posterior putamen, precuneus, semioval centre and temporal cortex. Associations were explored using fully adjusted multiple linear regression models. RESULTS: Participants had a mean (SD) age of 76.2 years (4.4) and 59.6% were female. The mean (SD) plasma 25(OH)D level was 22.4 ng/ml (10.8) and the mean (SD) cortical SUVR was 1.2 (0.2). We did not find any cross-sectional associations (p > 0.05) between baseline 25(OH)D levels and Abeta in any of the brain regions studied. CONCLUSIONS: These preliminary results suggest that circulating 25(OH)D is not associated with cerebral Abeta in older adults. Further longitudinal studies with the measurement of mid-life vitamin D status are required to explore the relationship between vitamin D and Abeta accrual over time, thereby circumventing the shortfalls of a cross-sectional study