Incidental findings on 3 T neuroimaging: cross-sectional observations from the population-based Rhineland Study

Purpose

Development of best practices for dealing with incidental findings on neuroimaging requires insight in their frequency and clinical relevance.

Methods

Here, we delineate prevalence estimates with 95% confidence intervals and clinical management of incidental findings, based on the first 3589 participants of the population-based Rhineland Study (age range 30–95 years) who underwent 3 Tesla structural neuroimaging (3D, 0.8 mm³ isotropic resolution). Two trained raters independently assessed all scans for abnormalities, with confirmation and adjudication where needed by neuroradiologists. Participants were referred for diagnostic work-up depending on the potential benefit.

Results

Of 3589 participants (mean age 55 ± 14 years, 2072 women), 867 had at least one possible incidental finding (24.2%). Most common were pituitary abnormalities (12.3%), arachnoid cysts (4.1%), developmental venous anomalies (2.5%), non-acute infarcts (1.8%), cavernomas (1.0%), and meningiomas (0.7%). Forty-six participants were informed about their findings, which was hitherto unknown in 40 of them (1.1%). Of these, in 19 participants (48%), a wait-and-see policy was applied and nine (23%) received treatment, while lesions in the remainder were benign, could not be confirmed, or the participant refused to inform us about their clinical diagnosis.

Conclusion

Nearly one-quarter of participants had an incidental finding, but only 5% of those required referral, that mostly remained without direct clinical consequences.

Automated olfactory bulb segmentation on high resolutional T2-weighted MRI

The neuroimage analysis community has neglected the automated segmentation of the olfactory bulb (OB) despite its crucial role in olfactory function. The lack of an automatic processing method for the OB can be explained by its challenging properties (small size, location, and poor visibility on traditional MRI scans). Nonetheless, recent advances in MRI acquisition techniques and resolution have allowed raters to generate more reliable manual annotations. Furthermore, the high accuracy of deep learning methods for solving semantic segmentation problems provides us with an option to reliably assess even small structures. In this work, we introduce a novel, fast, and fully automated deep learning pipeline to accurately segment OB tissue on sub-millimeter T2-weighted (T2w) whole-brain MR images. To this end, we designed a three-stage pipeline: (1) Localization of a region containing both OBs using FastSurferCNN, (2) Segmentation of OB tissue within the localized region through four independent AttFastSurferCNN - a novel deep learning architecture with a self-attention mechanism to improve modeling of contextual information, and (3) Ensemble of the predicted label maps. For this work, both OBs were manually annotated in a total of 620 T2w images for training (n=357) and testing. The OB pipeline exhibits high performance in terms of boundary delineation, OB localization, and volume estimation across a wide range of ages in 203 participants of the Rhineland Study (Dice Score (Dice): 0.852, Volume Similarity (VS): 0.910, and Average Hausdorff Distance (AVD): 0.215 mm). Moreover, it also generalizes to scans of an independent dataset never encountered during training, the Human Connectome Project (HCP), with different acquisition parameters and demographics, evaluated in 30 cases at the native 0.7 mm HCP resolution (Dice: 0.738, VS: 0.790, and AVD: 0.340 mm), and the default 0.8 mm pipeline resolution (Dice: 0.782, VS: 0.858, and AVD: 0.268 mm). We extensively validated our pipeline not only with respect to segmentation accuracy but also to known OB volume effects, where it can sensitively replicate age effects (β=-0.232, p<.01). Furthermore, our method can analyze a 3D volume in less than a minute (GPU) in an end-to-end fashion, providing a validated, efficient, and scalable solution for automatically assessing OB volumes.

Ten German versions of Rey's auditory verbal learning test: Age and sex effects in 4,000 adults of the Rhineland Study

INTRODUCTION

Detecting early pathological cognitive decline is critical for dementia and aging-related research and clinical diagnostics. Rey's Auditory Verbal Learning Test (AVLT) is commonly used to measure episodic verbal memory. The test requires participants to learn a list of 15 words over several trials. Since multiple testing is often required to detect cognitive decline, but repeating the same test can bias results, we developed 10 German AVLT word lists.

METHOD

We randomly assigned the lists to 4,000 participants (aged 30-94 years) from a population-based cohort to test their comparability, as well as aging effects and sex differences.

RESULTS

Nine lists were highly comparable, with only one being slightly more difficult. Recall performance decreased on average by 0.6-1.1 words per trial per decade of age. Perseveration errors decreased with increasing age. Women remembered on average between 0.8 and 1.5 words per trial more than men, regardless of age. Women also outperformed men in the sum of Trials 1-5, learning over trials, retroactive inhibition, and false-positive and interference errors. Proactive inhibition remained stable across age and was unaffected by sex.

CONCLUSION

This German AVLT version presents comparable lists including detailed age and sex references and therefore allows test repetition excluding training effects. These versions are a valuable resource for research and clinical application.

Evaluation of the Neuroanatomical Basis of Olfactory Dysfunction in the General Population

Importance

Olfactory dysfunction is a prodromal manifestation of many neurodegenerative disorders, including Alzheimer and Parkinson disease. However, its neuroanatomical basis is largely unknown.

Objective

To assess the association between olfactory brain structures and olfactory function in adults 30 years or older and to examine the extent to which olfactory bulb volume (OBV) mediates the association between central olfactory structures and olfactory function.

Design, Setting, and Participants

This cross-sectional study analyzed baseline data from the first 639 participants with brain magnetic resonance imaging (MRI) in the Rhineland Study, an ongoing population-based cohort study in Bonn, Germany. Participants were enrolled between March 7, 2016, and October 31, 2017, and underwent brain MRI and olfactory assessment. Data were analyzed from March 1, 2018, to June 30, 2021.

Exposure

Volumetric measures were derived from 3-T MRI T1-weighted brain scans, and OBV was manually segmented on T2-weighted images. The mean volumetric brain measures from the right and left sides were calculated, adjusted by head size, and normalized to all participants.

Main Outcomes and Measures

Performance on the 12-item smell identification test (SIT-12) was used as a proxy for olfactory function.

Results

A total of 541 participants with complete data on MRI-derived measures and SIT-12 scores were included. This population had a mean (SD) age of 53.6 (13.1) years and comprised 306 women (56.6%). Increasing age (difference in SIT-12 score, -0.04; 95% CI, -0.05 to -0.03), male sex (-0.26; 95% CI, -0.54 to 0.02), and nasal congestion (-0.28; 95% CI, -0.66 to 0.09) were associated with worse olfactory function (SIT-12 scores). Conversely, larger OBV was associated with better olfactory function (difference in SIT-12 score, 0.46; 95% CI, 0.29-0.64). Larger volumes of amygdala (difference in OBV, 0.12; 95% CI, 0.01-0.24), hippocampus (0.16; 95% CI, 0.04-0.28), insular cortex (0.12; 95% CI, 0.01-0.24), and medial orbitofrontal cortex (0.10; 95% CI, 0.00-0.20) were associated with larger OBV. Larger volumes of amygdala (volume × age interaction effect, 0.17; 95% CI, 0.03-0.30), parahippocampal cortex (0.17; 95% CI, 0.03-0.31), and hippocampus (0.21; 95% CI, 0.08-0.35) were associated with better olfactory function only in older age groups. The age-modified association between volumes of central olfactory structures and olfactory function was largely mediated through OBV.

Conclusions and Relevance

This cross-sectional study found that olfactory bulb volume was independently associated with odor identification function and was a robust mediator of the age-dependent association between volumes of central olfactory structures and olfactory function. Thus, neurodegeneration-associated olfactory dysfunction may primarily originate from the pathology of peripheral olfactory structures, suggesting that OBV may serve as a preclinical marker for the identification of individuals who are at an increased risk of neurodegenerative diseases.

Swarm Learning for decentralized and confidential clinical machine learning

Fast and reliable detection of patients with severe and heterogeneous illnesses is a major goal of precision medicine^1,2. Patients with leukaemia can be identified using machine learning on the basis of their blood transcriptomes³. However, there is an increasing divide between what is technically possible and what is allowed, because of privacy legislation^4,5. Here, to facilitate the integration of any medical data from any data owner worldwide without violating privacy laws, we introduce Swarm Learning—a decentralized machine-learning approach that unites edge computing, blockchain-based peer-to-peer networking and coordination while maintaining confidentiality without the need for a central coordinator, thereby going beyond federated learning. To illustrate the feasibility of using Swarm Learning to develop disease classifiers using distributed data, we chose four use cases of heterogeneous diseases (COVID-19, tuberculosis, leukaemia and lung pathologies). With more than 16,400 blood transcriptomes derived from 127 clinical studies with non-uniform distributions of cases and controls and substantial study biases, as well as more than 95,000 chest X-ray images, we show that Swarm Learning classifiers outperform those developed at individual sites. In addition, Swarm Learning completely fulfils local confidentiality regulations by design. We believe that this approach will notably accelerate the introduction of precision medicine.

Swarm Learning is a decentralized machine learning approach that outperforms classifiers developed at individual sites for COVID-19 and other diseases while preserving confidentiality and privacy.

Seroprevalence and correlates of SARS-CoV-2 neutralizing antibodies from a population-based study in Bonn, Germany

To estimate the seroprevalence and temporal course of SARS-CoV-2 neutralizing antibodies, we embedded a multi-tiered seroprevalence survey within an ongoing community-based cohort study in Bonn, Germany. We first assessed anti-SARS-CoV-2 immunoglobulin G levels with an immunoassay, followed by confirmatory testing of borderline and positive test results with a recombinant spike-based immunofluorescence assay and a plaque reduction neutralization test (PRNT). Those with a borderline or positive immunoassay result were retested after 4 to 5 months. At baseline, 4771 persons participated (88% response rate). Between April 24th and June 30th, 2020, seroprevalence was 0.97% (95% CI: 0.72-1.30) by immunoassay and 0.36% (95% CI: 0.21-0.61) when considering only those with two additional positive confirmatory tests. Importantly, about 20% of PRNT+ individuals lost their neutralizing antibodies within five months. Here, we show that neutralizing antibodies are detectable in only one third of those with a positive immunoassay result, and wane relatively quickly.

Insulin resistance accounts for metabolic syndrome-related alterations in brain structure

Metabolic syndrome (MetS) is a major public health burden worldwide and associated with brain abnormalities. Although insulin resistance is considered a pivotal feature of MetS, its role in the pathogenesis of MetS‐related brain alterations in the general population is unclear. Therefore, in 973 participants (mean age 52.5 years) of the population‐based Rhineland Study, we assessed brain morphology in relation to MetS and insulin resistance, and evaluated to what extent the pattern of structural brain changes seen in MetS overlap with those associated with insulin resistance. Cortical reconstruction and volumetric segmentation were obtained from high‐resolution brain images at 3 Tesla using FreeSurfer. The relations between metabolic measures and brain structure were assessed through (generalized) linear models. Both MetS and insulin resistance were associated with smaller cortical gray matter volume and thickness, but not with white matter or subcortical gray matter volume. Age‐ and sex‐adjusted vertex‐based brain morphometry demonstrated that MetS and insulin resistance were related to cortical thinning in a similar spatial pattern. Importantly, no independent effect of MetS on cortical gray matter was observed beyond the effect of insulin resistance. Our findings suggest that addressing insulin resistance is critical in the prevention of MetS‐related brain changes in later life.

Polypharmacy, potentially inappropriate medication and pharmacogenomics drug exposure in the Rhineland Study

AIM

High medication use may contribute to the efficiency of drug therapy in general, but it could also increase the burden of adverse drug reactions. We aimed to assess medication use and the prevalence of three risk factors for adverse drug reactions: the use of polypharmacy, potentially inappropriate medication in the elderly and pharmacogenomic polymorphisms affecting the metabolism of drugs.

METHODS

Cross-sectional interview-based medication data (including over-the-counter drugs) was collected in a large population-based cohort (≥30 years of age) in Bonn, Germany.

RESULTS

Analyses were based on the first 5000 participants of the Rhineland Study (mean age 55 years, 57% women). Of our participants, 66.0% reported the use of a drug regularly, which increased to 87.4% in participants aged ≥65 years (n = 1301). The rates of use of polypharmacy, potentially inappropriate medication and pharmacogenomic drugs were 15.9%, 6.4% and 20.5%, respectively. In participants <65 years, 16.0% (95% CI 14.8, 17.3) had at least one risk factor. In participants aged ≥65 years, 54.1% (95% CI 51.4, 56.8) had at least one and 27.4% (95% CI 25.0, 29.9) had at least two risk factors. Extrapolating these numbers to the German population implies that around 9 million of the 17 million individuals aged 65 years or older are potentially at an elevated risk for adverse drug reactions, of which 4.6 million are at a potentially highly elevated risk for adverse drug reactions.

CONCLUSION

Our study shows that drug use is common and the individual risk for an adverse drug reaction in our population is high. This suggests room for improvement in general medication use.

A Functional MRI Paradigm for Efficient Mapping of Memory Encoding Across Sensory Conditions

We introduce a new and time-efficient memory-encoding paradigm for functional magnetic resonance imaging (fMRI). This paradigm is optimized for mapping multiple contrasts using a mixed design, using auditory (environmental/vocal) and visual (scene/face) stimuli. We demonstrate that the paradigm evokes robust neuronal activity in typical sensory and memory networks. We were able to detect auditory and visual sensory-specific encoding activities in auditory and visual cortices. Also, we detected stimulus-selective activation in environmental-, voice-, scene-, and face-selective brain regions (parahippocampal place and fusiform face area). A subsequent recognition task allowed the detection of sensory-specific encoding success activity (ESA) in both auditory and visual cortices, as well as sensory-unspecific positive ESA in the hippocampus. Further, sensory-unspecific negative ESA was observed in the precuneus. Among others, the parallel mixed design enabled sustained and transient activity comparison in contrast to rest blocks. Sustained and transient activations showed great overlap in most sensory brain regions, whereas several regions, typically associated with the default-mode network, showed transient rather than sustained deactivation. We also show that the use of a parallel mixed model had relatively little influence on positive or negative ESA. Together, these results demonstrate a feasible, versatile, and brief memory-encoding task, which includes multiple sensory stimuli to guarantee a comprehensive measurement. This task is especially suitable for large-scale clinical or population studies, which aim to test task-evoked sensory-specific and sensory-unspecific memory-encoding performance as well as broad sensory activity across the life span within a very limited time frame.

Disease severity-specific neutrophil signatures in blood transcriptomes stratify COVID-19 patients

BACKGROUND

The SARS-CoV-2 pandemic is currently leading to increasing numbers of COVID-19 patients all over the world. Clinical presentations range from asymptomatic, mild respiratory tract infection, to severe cases with acute respiratory distress syndrome, respiratory failure, and death. Reports on a dysregulated immune system in the severe cases call for a better characterization and understanding of the changes in the immune system.

METHODS

In order to dissect COVID-19-driven immune host responses, we performed RNA-seq of whole blood cell transcriptomes and granulocyte preparations from mild and severe COVID-19 patients and analyzed the data using a combination of conventional and data-driven co-expression analysis. Additionally, publicly available data was used to show the distinction from COVID-19 to other diseases. Reverse drug target prediction was used to identify known or novel drug candidates based on finding from data-driven findings.

RESULTS

Here, we profiled whole blood transcriptomes of 39 COVID-19 patients and 10 control donors enabling a data-driven stratification based on molecular phenotype. Neutrophil activation-associated signatures were prominently enriched in severe patient groups, which was corroborated in whole blood transcriptomes from an independent second cohort of 30 as well as in granulocyte samples from a third cohort of 16 COVID-19 patients (44 samples). Comparison of COVID-19 blood transcriptomes with those of a collection of over 3100 samples derived from 12 different viral infections, inflammatory diseases, and independent control samples revealed highly specific transcriptome signatures for COVID-19. Further, stratified transcriptomes predicted patient subgroup-specific drug candidates targeting the dysregulated systemic immune response of the host.

CONCLUSIONS

Our study provides novel insights in the distinct molecular subgroups or phenotypes that are not simply explained by clinical parameters. We show that whole blood transcriptomes are extremely informative for COVID-19 since they capture granulocytes which are major drivers of disease severity.

Disease severity-specific neutrophil signatures in blood transcriptomes stratify COVID-19 patients

BACKGROUND

The SARS-CoV-2 pandemic is currently leading to increasing numbers of COVID-19 patients all over the world. Clinical presentations range from asymptomatic, mild respiratory tract infection, to severe cases with acute respiratory distress syndrome, respiratory failure, and death. Reports on a dysregulated immune system in the severe cases call for a better characterization and understanding of the changes in the immune system.

METHODS

In order to dissect COVID-19-driven immune host responses, we performed RNA-seq of whole blood cell transcriptomes and granulocyte preparations from mild and severe COVID-19 patients and analyzed the data using a combination of conventional and data-driven co-expression analysis. Additionally, publicly available data was used to show the distinction from COVID-19 to other diseases. Reverse drug target prediction was used to identify known or novel drug candidates based on finding from data-driven findings.

RESULTS

Here, we profiled whole blood transcriptomes of 39 COVID-19 patients and 10 control donors enabling a data-driven stratification based on molecular phenotype. Neutrophil activation-associated signatures were prominently enriched in severe patient groups, which was corroborated in whole blood transcriptomes from an independent second cohort of 30 as well as in granulocyte samples from a third cohort of 16 COVID-19 patients (44 samples). Comparison of COVID-19 blood transcriptomes with those of a collection of over 3100 samples derived from 12 different viral infections, inflammatory diseases, and independent control samples revealed highly specific transcriptome signatures for COVID-19. Further, stratified transcriptomes predicted patient subgroup-specific drug candidates targeting the dysregulated systemic immune response of the host.

CONCLUSIONS

Our study provides novel insights in the distinct molecular subgroups or phenotypes that are not simply explained by clinical parameters. We show that whole blood transcriptomes are extremely informative for COVID-19 since they capture granulocytes which are major drivers of disease severity.

Genome-wide association study identifies 48 common genetic variants associated with handedness

Handedness has been extensively studied because of its relationship with language and the over-representation of left-handers in some neurodevelopmental disorders. Using data from the UK Biobank, 23andMe and the International Handedness Consortium, we conducted a genome-wide association meta-analysis of handedness (N = 1,766,671). We found 41 loci associated (P < 5 × 10-8) with left-handedness and 7 associated with ambidexterity. Tissue-enrichment analysis implicated the CNS in the aetiology of handedness. Pathways including regulation of microtubules and brain morphology were also highlighted. We found suggestive positive genetic correlations between left-handedness and neuropsychiatric traits, including schizophrenia and bipolar disorder. Furthermore, the genetic correlation between left-handedness and ambidexterity is low (rG = 0.26), which implies that these traits are largely influenced by different genetic mechanisms. Our findings suggest that handedness is highly polygenic and that the genetic variants that predispose to left-handedness may underlie part of the association with some psychiatric disorders.

Strong age but weak sex effects in eye movement performance in the general adult population: Evidence from the Rhineland Study

Assessing physiological changes that occur with healthy ageing is prerequisite for understanding pathophysiological age-related changes. Eye movements are studied as biomarkers for pathological changes because they are altered in patients with neurodegenerative disorders. However, there is a lack of data from large samples assessing age-related physiological changes and sex differences in oculomotor performance. Thus, we assessed and quantified cross-sectional relations of age and sex with oculomotor performance in the general population. We report results from the first 4,000 participants (aged 30-95 years) of the Rhineland Study, a community-based prospective cohort study in Bonn, Germany. Participants completed fixation, smooth pursuit, prosaccade and antisaccade tasks. We quantified associations of age and sex with oculomotor outcomes using multivariable linear regression models. Performance in 12 out of 18 oculomotor measures declined with increasing age. No differences between age groups were observed in five antisaccade outcomes (amplitude-adjusted and unadjusted peak velocity, amplitude gain, spatial error and percentage of corrected errors) and for blink rate during fixation. Small sex differences occurred in smooth pursuit velocity gain (men have higher gain) and blink rate during fixation (men blink less). We conclude that performance declines with age in two thirds of oculomotor outcomes but that there was no evidence of sex differences in eye movement performance except for two outcomes. Since the percentage of corrected antisaccade errors was not associated with age but is known to be affected by pathological cognitive decline, it represents a promising candidate preclinical biomarker of neurodegeneration.

Associations of Hearing Sensitivity, Higher-Order Auditory Processing, and Cognition Over Time in Middle-Aged Adults

BACKGROUND

Age-related hearing loss (impairment in hearing sensitivity and/or higher-order auditory processing) and cognitive decline are common co-occurring impairments in elderly adults. Their relation in the process of aging remains insufficiently understood. We aim to assess the temporal relations of decline in hearing sensitivity, higher-order auditory processing, and cognition in middle-aged adults.

METHODS

This study included 1,274 Beaver Dam Offspring Study participants who participated in three examinations (baseline, 5-year, and 10-year follow-up). We assessed hearing sensitivity through pure-tone audiometry (PTA, averaged thresholds of 0.5, 1, 2, 4 kHz of the better ear), higher-order auditory processing as word recognition in competing message (WRCM) using the Northwestern University 6 word list in the better ear, and cognition through trail-making test performance (TMT). Linear mixed-effects models and linear regression models were used to determine associations over time and to what extent these measures influence each other over time.

RESULTS

The longitudinal decline between all functions was associated with the strongest relationships between PTA and WRCM. The effect of baseline PTA on WRCM 10 years later (standardized ß = -.30) was almost twice as big as the effect of baseline WRCM on PTA 10 years later (standardized ß = -.18). The effect of baseline WRCM on TMT 10 years later and vice versa were small (standardized ß = -.05). No directional relationship between PTA and TMT was identified (standardized ß ≤ .02).

CONCLUSIONS

While hearing sensitivity might affect higher-order auditory processing, associations between hearing and cognition appear bidirectional and weak in midlife. We need to be cautious before inferring causal effects of hearing on cognition.

Perceived stress but not hair cortisol concentration is related to adult cognitive performance

Chronic stress detrimentally affects cognition but evidence from population-based studies is scarce and largely based on one-dimensional stress assessments. In this study, we aimed to investigate associations of subjective and psychological chronic stress measures with cognition in a population-based sample of adults aged 30-95 years from the Rhineland Study. Participants completed the Perceived Stress Scale (subjective measure) and a cognitive test battery (N = 1766). Hair cortisol concentration (physiological measure) was assessed by liquid chromatography tandem mass spectrometry in 1098 participants. Cross-sectional associations between the two measures of chronic stress and cognition were investigated using multivariable linear regression models. Subjective and physiological measures of chronic stress were not associated with each other (B = 0.005 [95 %CI = -0.005 - 0.015]). Participants with higher perceived stress and specifically lower perceived self-efficacy performed worse in all cognitive domains (effect sizes ranged from β = -0.129 [95 %CI = -0.177 - -0.080] to -0.054 [95 %CI = -0.099 - -0.009]; and from β = 0.052 [95 %CI = 0.005 - 0.098] to 0.120 [95 %CI = 0.072 - 0.167], respectively). Relationships between subjective chronic stress measures and executive functioning were stronger in men compared to women (interaction β = -0.144 [95 %CI = -0.221 - -0.067]). Relationships between perceived stress and working memory, and between perceived self-efficacy and executive functioning, processing speed, verbal episodic and working memory, increased with older age. Hair cortisol concentration was not associated with performance in any cognitive domain. Our results suggest that subjective and physiological measures capture different aspects of chronic stress in the general population.

Association of retinal layer measurements and adult cognitive function: A population-based study

OBJECTIVE

To quantify the associations of peripapillary retinal nerve fiber layer (pRNFL) thickness and macular ganglion cell layer (mGCL) volume with cognitive functioning and to investigate how demographic and vascular health factors affect these associations in a population-based sample of adults.

METHODS

The sample included the first 3,000 participants (age range 30-95 years) of the Rhineland Study (recruited from March 2016 to December 2018) who underwent spectral-domain optical coherence tomography and cognitive assessment at 1 of 2 identical study centers in Bonn, Germany. We used multiple linear regression models to examine the relationships between retinal layer measurements and cognitive functioning after adjustment for confounders, and we examined the moderating effects of demographic and vascular health factors.

RESULTS

The analytical sample included 2,483 participants who were 54.3 years old (SD 13.8 years) on average. After full adjustment, each 1-SD decrease in mGCL volume was associated with a greater decrease in global function than that of pRNFL thickness (β = -0.048 [95% confidence interval (CI) -0.077 to -0.018] vs β = -0.021 [95% CI -0.049 to 0.007]). These relationships increased in strength with advancing age, were stronger in participants with hypertension, and were reversed in current smokers relative to nonsmokers.

CONCLUSIONS

mGCL volume is more strongly related to adult cognitive functioning than pRNFL thickness, making it a better potential biomarker of neurodegeneration. Age and vascular health factors play important roles in determining the strength and direction of this association.

Dementia Research Fit for the Planet: Reflections on Population Studies of Dementia for Researchers and Policy Makers Alike

In recent years, a rapidly increasing collection of investigative methods in addition to changes in diagnostic criteria for dementia have followed "high-tech" trends in medicine, with the aim to better define the dementia syndrome and its biological substrates, mainly in order to predict risk prior to clinical expression. These approaches are not without challenge. A set of guidelines have been developed by a group of European experts in population-based cohort research through a series of workshops, funded by the Joint Program for Neurodegenerative Disorders (JPND). The aims of the guidelines are to assist policy makers and researchers to understand (1) What population studies for ageing populations should encompass and (2) How to interpret the findings from population studies. Such studies are essential to provide evidence relevant to the understanding of healthy and frail brain ageing, including the dementia syndrome for contemporary and future societies by drawing on the past.

Metabolic Profiling of Human Plasma and Urine, Targeting Tryptophan, Tyrosine and Branched Chain Amino Acid Pathways

Tryptophan and tyrosine metabolism has a major effect on human health, and disorders have been associated with the development of several pathologies. Recently, gut microbial metabolism was found to be important for maintaining correct physiology. Here, we describe the development and validation of a UHPLC-ESI-MS/MS method for targeted quantification of 39 metabolites related to tryptophan and tyrosine metabolism, branched chain amino acids and gut-derived metabolites in human plasma and urine. Extraction from plasma was optimised using 96-well plates, shown to be effective in removing phospholipids. Urine was filtered and diluted ten-fold. Metabolites were separated with reverse phase chromatography and detected using triple quadrupole MS. Linear ranges (from ppb to ppm) and correlation coefficients (r² > 0.990) were established for both matrices independently and the method was shown to be linear for all tested metabolites. At medium spiked concentration, recovery was over 80% in both matrices, while analytical precision was excellent (CV < 15%). Matrix effects were minimal and retention time stability was excellent. The applicability of the methods was tested on biological samples, and metabolite concentrations were found to be in agreement with available data. The method allows the analysis of up to 96 samples per day and was demonstrated to be stable for up to three weeks from acquisition.

Previous Musical Experience and Cortical Thickness Relate to the Beneficial Effect of Motor Synchronization on Auditory Function

Auditory processing can be enhanced by motor system activity. During auditory-motor synchronization, motor activity guides auditory attention and thus facilitates auditory processing through active sensing. Previous research on enhanced auditory processing through motor synchronization has been limited to easy tasks with simple stimulus material. Further, the mechanisms and brain regions underlying this synchronization are unclear. We investigated the effect of motor synchronization on auditory processing with naturalistic, musical auditory material in a discrimination task. We further assessed how previous musical training and cortical thickness of specific brain regions relate to different aspects of auditory-motor synchronization. We conducted an auditory-motor experiment in 139 adults. The task involved melody discrimination and beat tapping synchronization. Additionally, 68 participants underwent structural MRI. We found that individuals with better auditory-motor synchronization accuracy showed improved melody discrimination, and that melody discrimination was better in trials with higher tapping accuracy. However, melody discrimination was worse in the tapping than in the listening only condition. Longer previous musical training and thicker Heschl's gyri were associated with better melody discrimination and better tapping synchrony. Post hoc analyses furthermore pointed to a possible moderating role of frontal regions. Our results suggest that motor synchronization can enhance auditory discrimination abilities through active sensing, but that this beneficial effect can be counteracted by dual-task inference when the two tasks are too challenging. Moreover, prior experience and structural brain differences influence the extent to which an individual can benefit from motor synchronization in complex listening. This could inform future research directed at development of personalized training programs for hearing ability.

Determinants of Macular Layers and Optic Disc Characteristics on SD-OCT: The Rhineland Study

Purpose

To investigate variation and determinants of macular layers, peripapillary retinal nerve fiber layer (pRNFL) and Bruch's membrane opening-minimum rim width (BMO-MRW) in the general population.

Methods

In 1306 participants, we performed spectral domain optical coherence tomography (SD-OCT) scans of the macula, pRNFL, and BMO-MRW, and assessed their determinants using multivariable regression. Intraindividual interocular differences were analyzed using Spearman's rank correlation analysis.

Results

Participant age ranged from 30 to 95 years (mean ± standard deviation, 56.1 ± 13.9) and 56% were women. Interocular correlation ranged from 0.63 to 0.93. Differences increased with age and were larger in persons with glaucoma or prior stroke. pRNFL and BMO-MRW decreased with increasing age. Except for RNFL, volumes of various inner macular layers and the outer nuclear layer (ONL) decreased with increasing age, more negative spherical equivalent (SE), and were lower in women compared to men. For some layers, age effects amplified over the life course. History of stroke was associated with smaller volumes of various layers, without reaching statistical significance. We found no association of further systemic parameters with any SD-OCT parameter.

Conclusions

We provide large-scale normative data from a Caucasian general population for various SD-OCT measures. Interocular variability increased with age and specific pathology. Factors, such as age, sex, refraction, and a history of stroke, were associated with various retinal assessments.

Translational Relevance

In clinical routine, our findings should be considered on a per eye basis when interpreting SD-OCT volumes, pRNFL, or BMO-MRW to avoid confounded results.

Vascular dysfunction-The disregarded partner of Alzheimer's disease

Increasing evidence recognizes Alzheimer's disease (AD) as a multifactorial and heterogeneous disease with multiple contributors to its pathophysiology, including vascular dysfunction. The recently updated AD Research Framework put forth by the National Institute on Aging-Alzheimer's Association describes a biomarker-based pathologic definition of AD focused on amyloid, tau, and neuronal injury. In response to this article, here we first discussed evidence that vascular dysfunction is an important early event in AD pathophysiology. Next, we examined various imaging sequences that could be easily implemented to evaluate different types of vascular dysfunction associated with, and/or contributing to, AD pathophysiology, including changes in blood-brain barrier integrity and cerebral blood flow. Vascular imaging biomarkers of small vessel disease of the brain, which is responsible for >50% of dementia worldwide, including AD, are already established, well characterized, and easy to recognize. We suggest that these vascular biomarkers should be incorporated into the AD Research Framework to gain a better understanding of AD pathophysiology and aid in treatment efforts.

Compressed Sensing Diffusion Spectrum Imaging for Accelerated Diffusion Microstructure MRI in Long-Term Population Imaging

Mapping non-invasively the complex microstructural architecture of the living human brain, diffusion magnetic resonance imaging (dMRI) is one of the core imaging modalities in current population studies. For the application in longitudinal population imaging, the dMRI protocol should deliver reliable data with maximum potential for future analysis. With the recent introduction of novel MRI hardware, advanced dMRI acquisition strategies can be applied within reasonable scan time. In this work we conducted a pilot study based on the requirements for high resolution dMRI in a long-term and high throughput population study. The key question was: can diffusion spectrum imaging accelerated by compressed sensing theory (CS-DSI) be used as an advanced imaging protocol for microstructure dMRI in a long-term population imaging study? As a minimum requirement we expected a high level of agreement of several diffusion metrics derived from both CS-DSI and a 3-shell high angular resolution diffusion imaging (HARDI) acquisition, an established imaging strategy used in other population studies. A wide spectrum of state-of-the-art diffusion processing and analysis techniques was applied to the pilot study data including quantitative diffusion and microstructural parameter mapping, fiber orientation estimation and white matter fiber tracking. When considering diffusion weighted images up to the same maximum diffusion weighting for both protocols, group analysis across 20 subjects indicates that CS-DSI performs comparable to 3-shell HARDI in the estimation of diffusion and microstructural parameters. Further, both protocols provide similar results in the estimation of fiber orientations and for local fiber tracking. CS-DSI provides high radial resolution while maintaining high angular resolution and it is well-suited for analysis strategies that require high b-value acquisitions, such as CHARMED modeling and biomarkers from the diffusion propagator.

Systemic and Ocular Determinants of Peripapillary Retinal Nerve Fiber Layer Thickness Measurements in the European Eye Epidemiology (E3) Population

PURPOSE

To investigate systemic and ocular determinants of peripapillary retinal nerve fiber layer thickness (pRNFLT) in the European population.

DESIGN

Cross-sectional meta-analysis.

PARTICIPANTS

A total of 16 084 European adults from 8 cohort studies (mean age range, 56.9±12.3-82.1±4.2 years) of the European Eye Epidemiology (E3) consortium.

METHODS

We examined associations with pRNFLT measured by spectral-domain OCT in each study using multivariable linear regression and pooled results using random effects meta-analysis.

MAIN OUTCOME MEASURES

Determinants of pRNFLT.

RESULTS

Mean pRNFLT ranged from 86.8±21.4 μm in the Rotterdam Study I to 104.7±12.5 μm in the Rotterdam Study III. We found the following factors to be associated with reduced pRNFLT: Older age (β = -0.38 μm/year; 95% confidence interval [CI], -0.57 to -0.18), higher intraocular pressure (IOP) (β = -0.36 μm/mmHg; 95% CI, -0.56 to -0.15), visual impairment (β = -5.50 μm; 95% CI, -9.37 to -1.64), and history of systemic hypertension (β = -0.54 μm; 95% CI, -1.01 to -0.07) and stroke (β = -1.94 μm; 95% CI, -3.17 to -0.72). A suggestive, albeit nonsignificant, association was observed for dementia (β = -3.11 μm; 95% CI, -6.22 to 0.01). Higher pRNFLT was associated with more hyperopic spherical equivalent (β = 1.39 μm/diopter; 95% CI, 1.19-1.59) and smoking (β = 1.53 μm; 95% CI, 1.00-2.06 for current smokers compared with never-smokers).

CONCLUSIONS

In addition to previously described determinants such as age and refraction, we found that systemic vascular and neurovascular diseases were associated with reduced pRNFLT. These may be of clinical relevance, especially in glaucoma monitoring of patients with newly occurring vascular comorbidities.

Variation in fibrinogen FGG and FGA genes and risk of stroke

Haplotypes of the fibrinogen gamma and alpha (FGG and FGA) genes are associated with the structure of the fibrin network and may therefore influence the risk of stroke. We investigated the relationship between common variation in these genes with ischemic and haemorrhagic stroke. The study was based on 6,275 participants of the prospective population-based Rotterdam Study who at baseline (1990 – 1993) were aged 55 years or over, free from stroke, and had successful assessment of at least one FGG or FGA single nucleotide polymorphisms (SNP). Common haplotypes were estimated using seven tagging SNPs across a 30 kb region containing the FGG and FGA genes. Follow-up for incident stroke was complete until January 1,2005. Associations between constructed haplotypes and risk of stroke were estimated with an age- and sex-adjusted logistic regression model. We observed 668 strokes, of which 393 were ischemic and 62 haemorrhagic, during a median follow-up time of 10.1 years. FGG+FGA haplotype 3 (H3) was associated with an increased risk of ischemic stroke (odds ratio [OR] 1.36, 95% confidence interval [CI] 1.09–1.69) and the risk estimate for hemorrhagic stroke was 0.71 (95% CI 0.46–1.09) compared to the most frequent H1. The FGG and FGA genes were not associated with stroke or its subtypes when analyzed separately. In conclusion, risk of ischemic stroke was higher in FGG+FGA H3 than in H1. The results suggested that an opposite association may exist for haemorrhagic stroke.