Dynamic X-ray Coherent Diffraction Analysis: Bridging the Time Scales between Imaging and Photon Correlation Spectroscopy.

The advent of diffraction limited sources and developments in detector technology opens up new possibilities for the study of materials in situ and operando. Coherent X-ray diffraction techniques such as coherent X-ray diffractive imaging (CXDI) and X-ray photon correlation spectroscopy (XPCS) are capable for this purpose and provide complementary information, although due to signal-to-noise requirements, their simultaneous demonstration has been limited. Here, we demonstrate a strategy for the simultaneous use of CXDI and XPCS to study in situ the Brownian motion of colloidal gold nanoparticles of 200 nm diameter suspended in a glycerol-water mixture. We visualize the process of agglomeration, examine the spatiotemporal space accessible with the combination of techniques, and demonstrate CXDI with 22 ms temporal resolution.

High-speed free-run ptychography at the Australian Synchrotron.

Over the last decade ptychography has progressed rapidly from a specialist ultramicroscopy technique into a mature method accessible to non-expert users. However, to improve scientific value ptychography data must reconstruct reliably, with high image quality and at no cost to other correlative methods. Presented here is the implementation of high-speed ptychography used at the Australian Synchrotron on the XFM beamline, which includes a free-run data collection mode where dead time is eliminated and the scan time is optimized. It is shown that free-run data collection is viable for fast and high-quality ptychography by demonstrating extremely high data rate acquisition covering areas up to 352 000 µm2 at up to 140 µm2 s-1, with 13× spatial resolution enhancement compared with the beam size. With these improvements, ptychography at velocities up to 250 µm s-1 is approaching speeds compatible with fast-scanning X-ray fluorescence microscopy. The combination of these methods provides morphological context for elemental and chemical information, enabling unique scientific outcomes.

Indication of retrograde tau spreading along Braak stages and functional connectivity pathways.

PURPOSE: Tau pathology progression in Alzheimer's disease (AD) is explained through the network degeneration hypothesis and the neuropathological Braak stages; however, the compatibility of these models remains unclear. METHODS: We utilized [18F]AV-1451 tau-PET scans of 39 subjects with AD and 39 sex-matched amyloid-negative healthy controls (HC) in the ADNI (Alzheimer's Disease Neuroimaging Initiative) dataset. The peak cluster of tau-tracer uptake was identified in each Braak stage of neuropathological tau deposition and used to create a seed-based functional connectivity network (FCN) using 198 HC subjects, to identify healthy networks unaffected by neurodegeneration. RESULTS: Voxel-wise tau deposition was both significantly higher inside relative to outside FCNs and correlated significantly and positively with levels of healthy functional connectivity. Within many isolated Braak stages and regions, the correlation between tau and intrinsic functional connectivity was significantly stronger than it was across the whole brain. In this way, each peak cluster of tau was related to multiple Braak stages traditionally associated with both earlier and later stages of disease. CONCLUSION: We show specificity of healthy FCN topography for AD-pathological tau as well as positive voxel-by-voxel correlations between pathological tau and healthy functional connectivity. We propose a model of "up- and downstream" functional tau progression, suggesting that tau pathology evolves along functional connectivity networks not only "downstream" (i.e., along the expected sequence of the established Braak stages) but also in part "upstream" or "retrograde" (i.e., against the expected sequence of the established Braak stages), with pathology in earlier Braak stages intensified by its functional relationship to later disease stages.

Clinical validity of second-generation tau PET tracers as biomarkers for Alzheimer's disease in the context of a structured 5-phase development framework.

PURPOSE: In 2017, the Geneva Alzheimer's disease (AD) strategic biomarker roadmap initiative proposed a framework of the systematic validation AD biomarkers to harmonize and accelerate their development and implementation in clinical practice. Here, we use this framework to examine the translatability of the second-generation tau PET tracers into the clinical context. METHODS: All available literature was systematically searched based on a set of search terms that related independently to analytic validity (phases 1-2), clinical validity (phase 3-4), and clinical utility (phase 5). The progress on each of the phases was determined based on scientific criteria applied for each phase and coded as fully, partially, preliminary achieved or not achieved at all. RESULTS: The validation of the second-generation tau PET tracers has successfully passed the analytical phase 1 of the strategic biomarker roadmap. Assay definition studies showed evidence on the superiority over first-generation tau PET tracers in terms of off-target binding. Studies have partially achieved the primary aim of the analytical validity stage (phase 2), and preliminary evidence has been provided for the assessment of covariates on PET signal retention. Studies investigating of the clinical validity in phases 3, 4, and 5 are still underway. CONCLUSION: The current literature provides overall preliminary evidence on the establishment of the second-generation tau PET tracers into the clinical context, thereby successfully addressing some methodological issues from the tau PET tracer of the first generation. Nevertheless, bigger cohort studies, longitudinal follow-up, and examination of diverse disease population are still needed to gauge their clinical validity.

The strategic biomarker roadmap for the validation of Alzheimer's diagnostic biomarkers: methodological update.

BACKGROUND: The 2017 Alzheimer's disease (AD) Strategic Biomarker Roadmap (SBR) structured the validation of AD diagnostic biomarkers into 5 phases, systematically assessing analytical validity (Phases 1-2), clinical validity (Phases 3-4), and clinical utility (Phase 5) through primary and secondary Aims. This framework allows to map knowledge gaps and research priorities, accelerating the route towards clinical implementation. Within an initiative aimed to assess the development of biomarkers of tau pathology, we revised this methodology consistently with progress in AD research. METHODS: We critically appraised the adequacy of the 2017 Biomarker Roadmap within current diagnostic frameworks, discussed updates at a workshop convening the Alzheimer's Association and 8 leading AD biomarker research groups, and detailed the methods to allow consistent assessment of aims achievement for tau and other AD diagnostic biomarkers. RESULTS: The 2020 update applies to all AD diagnostic biomarkers. In Phases 2-3, we admitted a greater variety of study designs (e.g., cross-sectional in addition to longitudinal) and reference standards (e.g., biomarker confirmation in addition to clinical progression) based on construct (in addition to criterion) validity. We structured a systematic data extraction to enable transparent and formal evidence assessment procedures. Finally, we have clarified issues that need to be addressed to generate data eligible to evidence-to-decision procedures. DISCUSSION: This revision allows for more versatile and precise assessment of existing evidence, keeps up with theoretical developments, and helps clinical researchers in producing evidence suitable for evidence-to-decision procedures. Compliance with this methodology is essential to implement AD biomarkers efficiently in clinical research and diagnostics.

Clinical considerations in individuals with α1-antitrypsin PI*SZ genotype.

α1-Antitrypsin deficiency (AATD), characterised by reduced levels or functionality of α1-antitrypsin (AAT), is a significantly underdiagnosed genetic condition that predisposes individuals to lung and liver disease. Most of the available data on AATD are based on the most common, severe deficiency genotype (PI*ZZ); therefore, treatment and monitoring requirements for individuals with the PI*SZ genotype, which is associated with a less severe AATD, are not as clear. Recent genetic data suggest the PI*SZ genotype may be significantly more prevalent than currently thought, due in part to less frequent identification in the clinic and less frequent reporting in registries. Intravenous AAT therapy, the only specific treatment for patients with AATD, has been shown to slow disease progression in PI*ZZ individuals; however, there is no specific evidence for AAT therapy in PI*SZ individuals, and it remains unclear whether AAT therapy should be considered in these patients. This narrative review evaluates the available data on the PI*SZ genotype, including genetic prevalence, the age of diagnosis and development of respiratory symptoms compared with PI*ZZ individuals, and the impact of factors such as index versus non-index identification and smoking history. In addition, the relevance of the putative 11 µM "protective threshold" for AAT therapy and the risk of liver disease in PI*SZ individuals is explored. The purpose of this review is to identify open research questions in this area, with the aim of optimising the future identification and management of PI*SZ individuals.

Dynamic coherent diffractive imaging using unsupervised identification of spatiotemporal constraints.

Dynamic coherent diffractive imaging (CDI) reveals the fine details of structural, chemical, and biological processes occurring at the nanoscale but imposes strict constraints on the object distribution and illumination. Ptychographic CDI relaxes these constraints by exploiting redundant information in data obtained from overlapping regions of an object, but its time resolution is inherently limited. We have extended ptychographic redundancy into the spatiotemporal domain in dynamic CDI, automatically identifying redundant information in time-series coherent diffraction data obtained from dynamic systems. Simulated synchrotron experiments show that high spatiotemporal resolution is achieved without a priori knowledge of the object or its dynamics.

Level of education mitigates the impact of tau pathology on neuronal function.

PURPOSE: Using PET imaging in a group of patients with Alzheimer's disease (AD), we investigated whether level of education, a proxy for resilience, mitigates the harmful impact of tau pathology on neuronal function. METHODS: We included 38 patients with mild-to-moderate AD (mean age 67 ± 7 years, mean MMSE score 24 ± 4, mean years of education 14 ± 4; 20 men, 18 women) in whom a [18F]AV-1451 scan (a measure of tau pathology) and an [18F]FDG scan (a measure of neuronal function) were available. The preprocessed PET scans were z-transformed using templates for [18F]AV-1451 and [18F]FDG from healthy controls, and subsequently thresholded at a z-score of ≥3.0, representing an one-tailed p value of 0.001. Next, three volumes were computed in each patient: the tau-specific volume (tau pathology without neuronal dysfunction), the FDG-specific volume (neuronal dysfunction without tau pathology), and the overlap volume (tau pathology and neuronal dysfunction). Mean z-scores and volumes were extracted and used as dependent variables in regression analysis with years of education as predictor, and age and MMSE score as covariates. RESULTS: Years of education were positively associated with tau-specific volume (ß = 0.362, p = 0.022), suggesting a lower impact of tau pathology on neuronal function in patients with higher levels of education. Concomitantly, level of education was positively related to tau burden in the overlap volume (ß = 0.303, p = 0.036) implying that with higher levels of education more tau pathology is necessary to induce neuronal dysfunction. CONCLUSION: In patients with higher levels of education, tau pathology is less paralleled by regional and remote neuronal dysfunction. The data suggest that early life-time factors such as level of education support resilience mechanisms, which ameliorate AD-related effects later in life.

Connectomics and molecular imaging in neurodegeneration.

Our understanding on human neurodegenerative disease was previously limited to clinical data and inferences about the underlying pathology based on histopathological examination. Animal models and in vitro experiments have provided evidence for a cell-autonomous and a non-cell-autonomous mechanism for the accumulation of neuropathology. Combining modern neuroimaging tools to identify distinct neural networks (connectomics) with target-specific positron emission tomography (PET) tracers is an emerging and vibrant field of research with the potential to examine the contributions of cell-autonomous and non-cell-autonomous mechanisms to the spread of pathology. The evidence provided here suggests that both cell-autonomous and non-cell-autonomous processes relate to the observed in vivo characteristics of protein pathology and neurodegeneration across the disease spectrum. We propose a synergistic model of cell-autonomous and non-cell-autonomous accounts that integrates the most critical factors (i.e., protein strain, susceptible cell feature and connectome) contributing to the development of neuronal dysfunction and in turn produces the observed clinical phenotypes. We believe that a timely and longitudinal pursuit of such research programs will greatly advance our understanding of the complex mechanisms driving human neurodegenerative diseases.

Networks of tau distribution in Alzheimer's disease.

See Whitwell (doi:10.1093/brain/awy001) for a scientific commentary on this article.A stereotypical anatomical propagation of tau pathology has been described in Alzheimer's disease. According to recent concepts (network degeneration hypothesis), this propagation is thought to be indicative of misfolded tau proteins possibly spreading along functional networks. If true, tau pathology accumulation should correlate in functionally connected brain regions. Therefore, we examined whether independent components could be identified in the distribution pattern of in vivo tau pathology and whether these components correspond with specific functional connectivity networks. Twenty-two 18F-AV-1451 PET scans of patients with amnestic Alzheimer's disease (mean age = 66.00 ± 7.22 years, 14 males/eight females) were spatially normalized, intensity standardized to the cerebellum, and z-transformed using the mean and deviation image of a healthy control sample to assess Alzheimer's disease-related tau pathology. First, to detect distinct tau pathology networks, the deviation maps were subjected to an independent component analysis. Second, to investigate if regions of high tau burden are associated with functional connectivity networks, we extracted the region with the maximum z-value in each of the generated tau pathology networks and used them as seeds in a subsequent resting-state functional MRI analysis, conducted in a group of healthy adults (n = 26) who were part of the 1000 Functional Connectomes Project. Third, to examine if tau pathology co-localizes with functional connectivity networks, we quantified the spatial overlap between the seed-based networks and the corresponding tau pathology network by calculating the Dice similarity coefficient. Additionally, we assessed if the tau-dependent seed-based networks correspond with known functional resting-state networks. Finally, we examined the relevance of the identified components in regard to the neuropathological Braak stages. We identified 10 independently coherent tau pathology networks with the majority showing a symmetrical bi-hemispheric expansion and coinciding with highly functionally connected brain regions such as the precuneus and cingulate cortex. A fair-to-moderate overlap was observed between the tau pathology networks and corresponding seed-based networks (Dice range: 0.13-0.57), which in turn resembled known resting-state networks, particularly the default mode network (Dice range: 0.42-0.56). Moreover, greater tau burden in the tau pathology networks was associated with more advanced Braak stages. Using the data-driven approach of an independent component analysis, we observed a set of independently coherent tau pathology networks in Alzheimer's disease, which were associated with disease progression and coincided with functional networks previously reported to be impaired in Alzheimer's disease. Together, our results provide novel information regarding the impact of tau pathology networks on the mechanistic pathway of Alzheimer's disease.

Tau-imaging in neurodegeneration.

Pathological cerebral aggregations of proteins are suggested to play a crucial role in the development of neurodegenerative disorders. For example, aggregation of the protein ß-amyloid in form of extracellular amyloid-plaques as well as intraneuronal depositions of the protein tau in form of neurofibrillary tangles represent hallmarks of Alzheimer's disease (AD). Recently, novel tracers for in vivo molecular imaging of tau-aggregates in the brain have been introduced, complementing existing tracers for imaging amyloid-plaques. Available data on these novel tracers indicate that the subject of Tau-PET may be of considerable complexity. On the one hand this refers to the various forms of appearance of tau-pathology in different types of neurodegenerative disorders. On the other hand, a number of hurdles regarding validation of these tracers still need to be overcome with regard to comparability and standardization of the different tracers, observed off-target/non-specific binding and quantitative interpretation of the signal. These issues will have to be clarified before systematic clinical application of this exciting new methodological approach may become possible. Potential applications refer to early detection of neurodegeneration, differential diagnosis between tauopathies and non-tauopathies and specific patient selection and follow-up in therapy trials.

Use of bacterial spores in monitoring water quality and treatment.

Because Clostridium perfringens spores are both specific to sewage contamination and environmentally stable, they are considered as possible conservative indicators of human fecal contamination and possible surrogates for environmentally stable pathogens. This review discusses the reasons and summarizes methods for monitoring spores in water. Cultural methods are still preferred over qPCR for routine water quality monitoring because of their low costs. Membrane filter (MF) methods are preferred over the more laborious and less accurate most probable number methods. The most commonly used MF media are TSC medium and mCP medium. TSC normally allows higher recoveries than mCP. TSC produces fewer false-positive results than mCP; however, it does produce more false-negatives. Two newer methods have substantial potential, CP Chromo Select agar, which allows better recoveries and greater specificity than mCP, and the Fung double tube method, which creates anaerobic conditions and allows enumeration of colonies in tubes in 5-6 hours. Aerobic spores are not associated with fecal contamination but they can be surrogates for environmentally stable pathogens in monitoring water for treatment efficacy; Bacillus cereus spores are normally measured on nutrient agar by the MF method.

Multimodal correlation of dynamic [18F]-AV-1451 perfusion PET and neuronal hypometabolism in [18F]-FDG PET.

PURPOSE: Cerebral glucose metabolism measured with [18F]-FDG PET is a well established marker of neuronal dysfunction in neurodegeneration. The tau-protein tracer [18F]-AV-1451 PET is currently under evaluation and shows promising results. Here, we assess the feasibility of early perfusion imaging with AV-1451 as a substite for FDG PET in assessing neuronal injury. METHODS: Twenty patients with suspected neurodegeneration underwent FDG and early phase AV-1451 PET imaging. Ten one-minute timeframes were acquired after application of 200 MBq AV-1451. FDG images were acquired on a different date according to clinical protocol. Early AV-1451 timeframes were coregistered to individual FDG-scans and spatially normalized. Voxel-wise intermodal correlations were calculated on within-subject level for every possible time window. The window with highest pooled correlation was considered optimal. Z-transformed deviation maps (ZMs) were created from both FDG and early AV-1451 images, comparing against FDG images of healthy controls. RESULTS: Regional patterns and extent of perfusion deficits were highly comparable to metabolic deficits. Best results were observed in a time window from 60 to 360 s (r = 0.86). Correlation strength ranged from r = 0.96 (subcortical gray matter) to 0.83 (frontal lobe) in regional analysis. ZMs of early AV-1451 and FDG images were highly similar. CONCLUSION: Perfusion imaging with AV-1451 is a valid biomarker for assessment of neuronal dysfunction in neurodegenerative diseases. Radiation exposure and complexity of the diagnostic workup could be reduced significantly by routine acquisition of early AV-1451 images, sparing additional FDG PET.

Effects of population density on corticosterone levels of prairie voles in the field.

High population density is often associated with increased levels of stress-related hormones, such as corticosterone (CORT). Prairie voles (Microtus ochrogaster) are a socially monogamous species known for their large population density fluctuations in the wild. Although CORT influences the social behavior of prairie voles in the lab, the effect of population density on CORT has not previously been quantified in this species in the field. We validated a non-invasive hormone assay for measuring CORT metabolites in prairie vole feces. We then used semi-natural enclosures to experimentally manipulate population density, and measured density effects on male space use and fecal CORT levels. Our enclosures generated patterns of space use and social interaction that were consistent with previous prairie vole field studies. Contrary to the positive relationship between CORT and density typical of other taxa, we found that lower population densities (80 animals/ha) produced higher fecal CORT than higher densities (240/ha). Combined with prior work in the lab and field, the data suggest that high prairie vole population densities indicate favorable environments, perhaps through reduced predation risk. Lastly, we found that field animals had lower fecal CORT levels than laboratory-living animals. The data emphasize the usefulness of prairie voles as models for integrating ecological, evolutionary, and mechanistic questions in social behavior.

Age trajectories of functional activation under conditions of low and high processing demands: an adult lifespan fMRI study of the aging brain.

We examined functional activation across the adult lifespan in 316 healthy adults aged 20-89years on a judgment task that, across conditions, drew upon both semantic knowledge and ability to modulate neural function in response to cognitive challenge. Activation in core regions of the canonical semantic network (e.g., left IFG) were largely age-invariant, consistent with cognitive aging studies that show verbal knowledge is preserved across the lifespan. However, we observed a steady linear increase in activation with age in regions outside the core network, possibly as compensation to maintain function. Under conditions of increased task demands, we observed a stepwise reduction across the lifespan of modulation of activation to increasing task demands in cognitive control regions (frontal, parietal, anterior cingulate), paralleling the neural equivalent of "processing resources" described by cognitive aging theories. Middle-age was characterized by decreased modulation to task-demand in subcortical regions (caudate, nucleus accumbens, thalamus), and very old individuals showed reduced modulation to task difficulty in midbrain/brainstem regions (ventral tegmental, substantia nigra). These novel findings suggest that aging of activation to demand follows a gradient along the dopaminergic/nigrostriatal system, with earliest manifestation in fronto-parietal regions, followed by deficits in subcortical nuclei in middle-age and then to midbrain/brainstem dopaminergic regions in the very old.

Obesity and Aging: Consequences for Cognition, Brain Structure, and Brain Function.

OBJECTIVES: This review focuses on the relationship between obesity and aging and how these interact to affect cognitive function. The topics covered are guided by the Scaffolding Theory of Aging and Cognition (STAC [Park and Reuter-Lorenz. Annu Rev Psychol 2009;60:173-96]-a conceptual model designed to relate brain structure and function to one's level of cognitive ability. METHODS: The initial literature search was focused on normal aging and was guided by the key words, "aging, cognition, and obesity" in PubMed. In a second search, we added key words related to neuropathology including words "Alzheimer's disease," "vascular dementia," and "mild cognitive impairment." RESULTS: The data suggest that being overweight or obese in midlife may be more detrimental to subsequent age-related cognitive decline than being overweight or obese at later stages of the life span. These effects are likely mediated by the accelerated effects obesity has on the integrity of neural structures, including both gray and white matter. Further epidemiological studies have provided evidence that obesity in midlife is linked to an increased risk for Alzheimer's disease and vascular dementia, most likely via an increased accumulation of Alzheimer's disease pathology. CONCLUSIONS: Although it is clear that obesity negatively affects cognition, more work is needed to better understand how aging plays a role and how brain structure and brain function might mediate the relationship of obesity and age on cognition. Guided by the STAC and the STAC-R models, we provide a roadmap for future investigations of the role of obesity on cognition across the life span.

A field evaluation of the Eye-Closure Interview with witnesses of serious crimes.

Laboratory research shows that eye-closure during memory retrieval improves both the amount and the factual accuracy of memory reports about witnessed events. Based on these findings, we developed the Eye-Closure Interview, and examined its feasibility (in terms of compliance with the instructions) and effectiveness (in terms of the quantity and quality of reported information) in eyewitness interviews conducted by the South African Police Service. Police interviewers from the Facial Identification Unit were randomly assigned to receive Eye-Closure Interview training or no training. We analyzed 95 interviews with witnesses of serious crimes (including robbery, rape, and murder), some of whom were instructed to close their eyes during salient parts of the interview. Witnesses in the control condition rarely spontaneously closed their eyes, but witnesses in the Eye-Closure Interview condition kept their eyes closed during 97% of their descriptions, suggesting that the Eye-Closure Interview would be easy to implement in a field setting. Although witnesses who closed their eyes did not remember more information overall, the information they provided was considered to be of significantly greater forensic relevance (as reflected in 2 independent blind assessments, 1 by a senior police expert and 1 by a senior researcher). Thus, based on the findings from this field study and from previous laboratory research, we conclude that implementation of the Eye-Closure Interview in witness interviews would help police interviewers to elicit more valuable information from witnesses, which could be relevant to the police investigation and/or in court. (PsycINFO Database Record