Phase Variations in fMRI Time Series Analysis: Friend or Foe?

Functional MRI studies (fMRI) are based on the blood-oxygenation-level-dependent effect (BOLD) that arises in brain areas where neuronal activity takes place (Ogawa et al., 1990, 1993). BOLD induces changes in the local magnetic susceptibility and these can be measured by Gradient Echo (GE) Echo-Planar-Imaging (EPI). The fMRI signal thus observed consists of a complex value, which can be subdivided into a magnitude and a phase value, but in most fMRI studies the phase signal is discarded and only the magnitude changes are used to detect the activated brain areas

Preliminary Integrated Chronostratigraphy of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica

We use all available chronostratigraphic constraints – biostratigraphy, magnetostratigraphy, radioisotopic dates, strontium-isotope stratigraphy, and correlation of compositional and physical properties to well-dated global or regional records – to construct a preliminary age model for ANDRILL SMS Project’s AND-2A drillcore (77°45.488’S, 165°16.605’E, 383.57 m water depth). These diverse chronostratigraphic constraints are consistent with each other and are distributed throughout the 1138.54 m-thick section, resulting in a well-constrained age model. The sedimentary succession comprises a thick early and middle Miocene section below 224.82 mbsf and a condensed middle/late Miocene to Recent section above this. The youngest sediments are Brunhes age (<0.781 Ma), as confirmed by a radioisotopic age of 0.691±0.049 Ma at 10.23 mbsf and the occurrence of sediments that have normal magnetic polarity down to ~31.1 mbsf, which is interpreted to be the Brunhes/Matuyama reversal (0.781 Ma). The upper section is punctuated by disconformities resulting from both discontinuous deposition and periods of extensive erosion typical of sedimentary environments at the margin of a dynamic ice sheet. Additional breaks in the section may be due to the influence of tectonic processes. The age model incorporates several major hiatuses but their precise depths are still somewhat uncertain, as there are a large number of erosional surfaces identified within the stratigraphic section. One or more hiatuses, which represent a total 7 to 8 million years of time missing from the sedimentary record, occur between about 50 mbsf and the base of Lithostratigraphic Unit (LSU) 3 at 122.86 mbsf. Similarly, between about 145 mbsf and the base of LSU 4 at 224.82 mbsf, one or more hiatuses occur on which another 2 to 3 million years of the sedimentary record is missing. Support for the presence of these hiatuses comes from a diatom assemblage that constrains the age of the core from 44 to 50 mbsf to 2.06-2.84 Ma, two radioisotopic dates (11.4 Ma) and a Sr‑isotope date (11.7 Ma) that indicate the interval from 127 to 145 mbsf was deposited between 11.4 and 11.7 Ma, and three diatom occurrence datums from between 225.38 and 278.55 mbsf that constrain the age of this upper part of Lithostratigraphic Unit (LSU) 5 to 14.29 - 15.89 Ma. Below the boundary between LSU 5 and 6 sedimentation was relatively continuous and rapid and the age model is well-constrained by 9 diatom datums, seven 40Ar-39Ar dates, one Sr-isotope date, and 19 magnetozones. Even so, short hiatuses (less than a few hundred thousand years) undoubtedly occur but are beyond the resolution of current chronostratigraphic age constraints. Diatom first and last occurrence datums provide particularly good age control from the top of LSU 6 down to 771.5 mbsf (in LSU 10), where the First Occurrence (FO) of Thalassiosira praefraga (18.85 Ma) is observed. The diatom datum ages are supported by radioisotopic dates of 17.30±0.31 Ma at 640.14 mbsf (in LSU 9) and 18.15±0.35 and 17.93±0.40 Ma for samples from 709.15 and 709.18 mbsf (in LSU 10), respectively, and 18.71±0.33 Ma for a sample from 831.67 mbsf (in LSU 11). The sediments from 783.69 mbsf to the base of the hole comprise two thick normal polarity magnetozones that bound a thinner reversed polarity magnetozone (958.59 - 985.64 mbsf). This polarity sequence most likely encompasses Chrons C5En, C5Er, and C6n (18.056 - 19.772 Ma or slightly older given uncertainties in this section of the geomagnetic polarity timescale), but could be also be Chrons C6n, C6r, and C6An.1n (18.748 - 20.213 Ma). Either polarity sequence is compatible with the 40Ar–39Ar age of 20.01±0.35 Ma obtained from single-grain analyses of alkali feldspar from a tephra sample from a depth of 1093.02 mbsf, although the younger interpretation allows a better fit with chronostratigraphic data up-core. Given this age model, the mean sedimentation rate is about 18 cm/k.y. from the top of LSU 6 to the base of the hole.Published221-2202.2. Laboratorio di paleomagnetismoN/A or not JCRreserve

Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene

Biophysical modelling of the effect of Alzheimer's plaques on MRI

The strong difference in magnetic susceptibility, χ, between white and grey matter (WM and GM) in Alzheimer’s Disease (AD) can be used to distinguish between AD patients and healthy controls (Acosta-Cabronero et. al, 2013; Van Rooden et., al, 2014). However, the cause behind this difference has not yet been established. Here, we performed biophysical modelling to investigate the contribution from iron-rich β-amyloid plaques to the MRI signal. Field maps were generated using the plaques spatial distribution obtained from β-amyloid stained histologic sections. Histologic section of post mortem tissue from the frontal cortex of an AD patient stained for β-amyloid was used to determine the spatial distribution of the plaques in microscopic images with a voxel size of 25µm. High resolution MRI was used to estimate the maximal magnetic susceptibility effect of the plaques. Biophysical modelling was performed and maps of the magnetic field caused by the plaques using a voxel size of 25µm were generated. The magnetic field was then averaged for different isotropic voxel sizes (100, 500, 750 and 1000µm). At small voxel sizes (≤100µm) the magnetic field effect caused by single β-amyloid plaques could be observed (Fig. 1). At the voxel size of 100µm, which is close to the spatial resolution achievable with clinical protocols at ultra high field strenght (≥7T), single plaques effects could not be observed. However, a clear pattern due to the palques can be distinguished at this spatial resolution (Fig. 2). For greater voxel sizes (500µ and 750µm), only the combined effect of several plaques was detectable. However, even at voxel sizes of 1mm, that can be used on clinical scanners operating at 3T, the magnetic field effect was still noticeable (Fig. 3). Our modelling results show that iron-rich β-amyloid plaques cannot be directly observed using clinical MRI scanners. However, they may still contribute significantly to the alterations observed in Alzheimer's patients using quantitative MRI. This is of pivotal importance, because they potentially may contribute to the diagnosis of Alzheimer's Disease

The bioethical debate between Laicism and Catholicism on the self-determination of death and dying. Gathering of logical substratum over and above opposites

The study considers two corpora that confront the themes of the end of life: the first is constituted by 12 contributions of a book edited by the Fondazione Umberto Veronesi (2006) and the second by 13 contributions of an International Congress organized by the Pontificia Accademia Pro Vita (2008). To underline similarities and differences of the lexical profiles the two groups of opposite contributions have been compared and contrasted using qualitative and quantitative perspectives. The research identifies and describes the pivot concepts that justify the contraposition. This work is really important because it shows a methodological way to demonstrate the procedure useful for a critical analysis of the contents that are involved in the bioethical debate. In fact it is a very rare experiment in this field, and so it opens a new view on the possibility to render methodologically more evident the comparison on which the political and social choices depend

Record of the early Holocene warming in a laminated sediment core from Cape Hallett Bay (Northern Victoria Land, Antarctica).

This paper presents an integrated multiproxy approach study (sedimentological, geochemical, preliminary smear-slides diatom assemblages, and 14C ages analyses) performed on a sediment core collected in Cape Hallett Bay (Ross Sea, Antarctica). Sediments record the early Holocene rapid climate changes: buried varved diatomaceous ooze on the base of core (N9.5\u20139.4 ka BP) are linked to the early Holocene warming and open marine conditions. From 9.4 ka BP, the climate starts to cool (massive mud). From 8.0 to 7.8 ka BP, sandy mud sediment suggests a rapid landward recession of the local/regional glaciers, with relevant underflow inputs, together with the onset of seasonal sea-ice formation. The ages and the characteristics of the youngest sediments are related to the changed oceanographic conditions linked to the retreat of the calving front of the Ross Ice Shelf

Improvement of R2* mapping in Alzheimer’s Disease at 9.4T through reduction of B0 fluctuation-induced image artifacts using Navigator Echoes

Ultra-High-Field (UHF) MRI provides a potential non-invasive means to investigate Alzheimer’s Disease (AD). R2* map is one of the most established MRI techniques to detect iron concentration in the brain. However, image quality can be substantially affected by B0 fluctuation-related-artifacts at UHF. In this study we showed an improvement of the quality of R2* maps in AD at 9.4T using Navigator Echos approach

Longitudinal evaluation of Scanner Performance for fMRI studies at 3T: a comparison of quality parameters across 8 years

We assessed the parameter λ which represents a physical measure of the spatial degradation of the temporal SNR within each run due to fluctuations related to scanner instabilities