Search

Introduction Autopsy studies recognize the locus coeruleus (LC) as one of the first sites accumulating tau in Alzheimer's disease (AD). Recent AD work related in vivo LC magnetic resonance imaging (MRI) integrity to tau and cognitive decline; however, relationships of LC integrity to age, tau, and cognition in autosomal dominant AD (ADAD) remain unexplored. Methods We associated LC integrity (3T-MRI) with estimated years of onset, cortical amyloid beta, regional tau (positron emission tomography [PET]) and memory (Consortium to Establish a Registry for Alzheimer's Disease (CERAD) Word-List-Learning) among 27 carriers and 27 non-carriers of the presenilin-1 (PSEN1) E280A mutation. Longitudinal changes between LC integrity and tau were evaluated in 10 carriers. Results LC integrity started to decline at age 32 in carriers, 12 years before clinical onset, and 20 years earlier than in sporadic AD. LC integrity was negatively associated with cortical tau, independent of amyloid beta, and predicted precuneus tau increases. LC integrity was positively associated with memory. Discussion These findings support LC integrity as marker of disease progression in preclinical ADAD.

Background and ObjectivesAlzheimer disease (AD) clinical trials are moving earlier in the disease process according to emerging signs of β-amyloid (Aβ) and tau pathology. If early treatment is the right time for intervention, it is critical to find the right test to optimize cognitive outcome measures for clinical trials. We sought to identify cognitive measures associated with the earliest detectable signs of emerging Aβ and tau pathology.MethodsOne hundred twelve clinically normal adults with longitudinal Pittsburgh compound B (PiB)-PET, 18F-flortaucipir (FTP)-PET, and cognitive data for ≥7 years were included from the Harvard Aging Brain Study (HABS). Analyses assessed those initially classified as PiB− (less than Centiloid [CL] 20) and then expanded to include PiB+ individuals up to CL40, the approximate threshold beyond which neocortical tau proliferation begins. Separate linear mixed-effects models assessed the effects of emerging global Aβ (PiB slope) and tau (baseline FTP level and FTP slope) in the entorhinal and inferior temporal (IT) cortices on multiple cognitive tasks and the Preclinical Alzheimer's Cognitive Composite (PACC) over time.ResultsSteeper PiB slopes were associated with declining processing speed (Digit Symbol Substitution Test [DSST], Trail Making Test Part A) in those CL40).DiscussionEarly, Aβ-mediated cognitive slowing was detected for processing speed measures, while early memory retrieval declines were associated with emerging Aβ and tau pathology. Composites of these measures may help determine whether anti-Aβ or anti-tau therapies administered at the first signs of pathology might preserve cognitive function.Classification of EvidenceThis study provides Class I evidence that in clinically normal older adults, emerging PET-detected AD pathology is associated with declining processing speeds and memory retrieval.

The neural correlates of subjective cognitive decline (SCD; i.e., without objectifiable deficit) remain to be elucidated. Possible causes of SCD include early neurodegeneration related to Alzheimer's disease or functional and structural changes related to sub-clinical depression. We investigated the relationship between episodic memory performance or memory complaints and structural or functional magnetic resonance imaging (MRI) measures in participants with SCD ( n = 18) but without psychiatric disorders and healthy controls ( n = 31). In SCD, memory complaints were not associated with memory performance but with sub-clinical depression and executive functions. SCD-associated memory complaints correlated with higher amygdala and parahippocampal gyrus (specifically subiculum) gray matter density. In controls, but not in SCD, mesiotemporal gray matter density and superior frontal gyrus functional connectivity predicted memory performance. In contrast, in SCD, only a trend toward a correlation between memory performance and gray matter density in the parietooccipital lobes was observed. In our memory-clinic sample of SCD, we did not observe incipient neurodegeneration (limited to structural and functional MRI) but rather sub-clinical depression underlying subjective cognitive complaints. (c) 2021 Elsevier Inc. All rights reserved.

Advanced Alzheimer's disease (AD) is characterized by higher noradrenaline metabolite levels that may be associated with AD pathology. The locus coeruleus (LC) is the main site for cerebral noradrenaline synthesis and LC volume loss occurs as early as Braak stage 1. This study investigates the association between noradrenergic turnover and brain morphology, and the modifying effect of AD pathology. The study sample included 77 memory clinic patients (37 cognitively unimpaired and 40 cognitively impaired (mild cognitive impairment or AD dementia)). Cortical thickness and volumetric analyses were performed using FreeSurfer. Cerebrospinal fluid was analyzed for noradrenergic metabolite 3-methoxy-4hydroxyphenylethyleneglycol (MHPG), A beta 42 and phosphorylated tau. Higher MHPG was associated with lower cortical thickness and hippocampal volume at lower, but subthreshold, levels of A beta 42 and at higher p-tau levels. These associations remained significant after adding APOE-E4 or cognitive status as covariates. Our results suggest that greater MHPG together with worse AD pathology contributes to neurodegeneration, possibly before significant amyloidosis. The noradrenergic system may play an important role in early detection of AD-related processes. (C) 2021 The Authors. Published by Elsevier Inc.

OBJECTIVE: Women have a higher lifetime risk of AD than men. Among cognitively normal (CN) older adults, women exhibit elevated tau positron emission tomography (PET) signal compared with men. We explored whether menopause exacerbates sex differences in tau deposition in middle-aged adults.METHODS: 328 CN participants from the Framingham Study (mean age=57yrs(±10yrs), 161 women, of whom, 104 were post-menopausal) underwent tau and β-amyloid (Aβ)-PET neuroimaging. We examined global Aβ-PET, and tau-PET signal in five regions identified a priori as demonstrating significant sex differences in older adults (in temporal, inferior parietal, middle frontal, and lateral occipital regions). We examined sex and menopause status-related differences in each region-of-interest, using linear regressions, as well as interactions with Aβ and APOEε4 genotype.RESULTS: Women exhibited higher tau-PET signal (pINTERPRETATION: Clear divergence in tauopathy between the sexes are apparent approximately 20 years earlier than previously reported. Menopause status moderated sex differences in Aβ and tau-PET burden, with tau first appearing post-menopause. Sex and menopause differences consistently appeared in middle frontal and parieto-occipital regions but were not moderated by Aβ burden or APOEε4, suggesting that menopause-related tau vulnerability may be independent of AD-related pathways. This article is protected by copyright. All rights reserved.

Five decades ago, seminal studies positioned the brainstem locus coeruleus (LC) norepinephrine (NE) system as a key substrate for the regulation of wakefulness and sleep, and this picture has recently been elaborated thanks to methodological advances in the precise investigation and experimental modulation of LC structure and functions. This review presents and discusses findings that support the major role of the LC-NE system at different levels of sleep-wake organization, ranging from its involvement in the overall architecture of the sleep-wake cycle to its associations with sleep microstructure, while accounting for the intricate neuroanatomy surrounding the LC. Given the particular position held by the LC NE system by being at the intersection of sleep-wake dysregulation and initial pathophysiological processes of Alzheimer's disease (AD), we conclude by examining emerging opportunities to investigate LC NE mediated relationships between sleep-wake alteration and AD in human aging. We further propose several research perspectives that could support the LC-NE system as a promising target for the identification of at-risk individuals in the preclinical stages of AD, and for the development of novel preventive interventions. ?? 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

ObjectiveTo identify the hippocampal subregions linking initial amyloid and tau pathology to memory performance in clinically normal older individuals, reflecting preclinical Alzheimer disease (AD).MethodsA total of 127 individuals from the Harvard Aging Brain Study (mean age 76.22 ± 6.42 years, 68 women [53.5%]) with a Clinical Dementia Rating score of 0, a flortaucipir tau-PET scan, a Pittsburgh compound B amyloid-PET scan, a structural MRI scan, and cognitive testing were included. From these images, we calculated neocortical, hippocampal, and entorhinal amyloid pathology; entorhinal and hippocampal tau pathology; and the volumes of 6 hippocampal subregions and total hippocampal volume. Memory was assessed with the selective reminding test. Mediation and moderation analyses modeled associations between regional markers and memory. Analyses included covariates for age, sex, and education.ResultsNeocortical amyloid, entorhinal tau, and presubiculum volume univariately associated with memory performance. The relationship between neocortical amyloid and memory was mediated by entorhinal tau and presubiculum volume, which was modified by hippocampal amyloid burden. With other biomarkers held constant, presubiculum volume was the only marker predicting memory performance in the total sample and in individuals with elevated hippocampal amyloid burden.ConclusionsThe presubiculum captures unique AD-related biological variation that is not reflected in total hippocampal volume. Presubiculum volume may be a promising marker of imminent memory problems and can contribute to understanding the interaction between incipient AD-related pathologies and memory performance. The modulation by hippocampal amyloid suggests that amyloid is a necessary, but not sufficient, process to drive neurodegeneration in memory-related regions.

Neuroimaging studies have revealed important pathomechanisms related to disorders of brain-gut interactions, such as irritable bowel syndrome and functional dyspepsia. More detailed investigations aimed at neural processing in the brainstem, including the key relay station of the nucleus of the solitary tract (NTS), have hitherto been hampered by technical shortcomings. To ascertain these processes in more detail, we used multi-echo multiband 7T functional magnetic resonance imaging (fMRI) and a novel translational experimental model based on a nutrient-derived intestinal chemonociceptive stimulus. In a randomized cross-over fashion, subjects received duodenal infusion of capsaicin (the pungent principal in red peppers) and placebo (saline). During infusion, fMRI data and concomitant symptom ratings were acquired. Of 26 healthy female volunteers included, 18 were included in the final analysis. Significantly increased brain activation over time during capsaicin infusion, as compared to placebo, was observed in brain regions implicated in pain processing, in particular the NTS. Brain activation in the thalamus, cingulate cortex and insula were more pronounced in subjects who reported abdominal pain (visual analogue scale > 10mm), as compared to subjects who experienced no pain. On the contrary, activations at the level of the NTS were independent of subjective pain ratings. The current experimental paradigm therefore allowed us to demonstrate activation of the principal relay station for visceral afferents in the brainstem, the NTS, which was engaged irrespective of the conscious pain response. These findings contribute to understanding the fundamental mechanism necessary for developing novel therapies aimed at correcting disturbances in visceral afferent pain processing.

The vascular and neurodegenerative processes related to clinical dementia cause cell loss which induces, amongst others, an increase in interstitial fluid (ISF).We assessed microvascular, parenchymal integrity, and a proxy of ISF volume alterations with intravoxel incoherent motion imaging in 21 healthy controls and 53 memory clinic patients - mainly affected by neurodegeneration (mild cognitive impairment, Alzheimer's disease dementia), vascular pathology (vascular cognitive impairment), and presumed to be without significant pathology (subjective cognitive decline).The microstructural components were quantified with spectral analysis using a non-negative least squares method. Linear regression was employed to investigate associations of these components with hippocampal and white matter hyperintensity (WMH) volumes. In the normal appearing white matter, a large f(int )(a proxy of ISF volume) was associated with a large WMH volume and low hippocampal volume. Likewise, a large f(int) value was associated with a lower hippocampal volume in the hippocampi.Large ISF volume (f(int)) was shown to be a prominent factor associated with both WMHs and neurodegenerative abnormalities in memory clinic patients and is argued to play a potential role in impaired glymphatic functioning. (C) 2021 The Author(s). Published by Elsevier Inc.

ObjectiveTo compare how structural MRI, fluorodeoxyglucose (FDG), and flortaucipir (FTP) PET signals predict cognitive decline in high-amyloid vs low-amyloid participants with the goal of determining which biomarker combination would result in the highest increase of statistical power for prevention trials.MethodsIn this prospective cohort study, we analyzed data from clinically normal adults from the Harvard Aging Brain Study with MRI, FDG, FTP, and Pittsburgh compound B (PiB)-PET acquired within a year and prospective cognitive evaluations over a mean 3-year follow-up. We focused analyses on predefined regions of interest: inferior temporal, isthmus cingulate, hippocampus, and entorhinal cortex. Cognition was assessed with the Preclinical Alzheimer's Cognitive Composite. We evaluated the association between biomarkers and cognitive decline using linear mixed-effect models with random intercepts and slopes, adjusting for demographics. We generated power curves simulating prevention trials.ResultsData from 131 participants (52 women, age 73.98 ± 8.29 years) were analyzed in the study. In separate models, most biomarkers had a closer association with cognitive decline in the high-PiB compared to the low-PiB participants. A backward stepwise regression including all biomarkers demonstrated that only neocortical PiB, entorhinal FTP, and entorhinal FDG were independent predictors of subsequent cognitive decline. Power analyses revealed that using both high PiB and low entorhinal FDG as inclusion criteria reduced 3-fold the number of participants needed in a hypothetical trial compared to using only high PiB.DiscussionIn preclinical Alzheimer disease, entorhinal hypometabolism is a strong and independent predictor of subsequent cognitive decline, making FDG a potentially useful biomarker to increase power in clinical trials.Classification of EvidenceThis study provides Class II evidence that in people with preclinical Alzheimer disease, entorhinal hypometabolism identified by FDG-PET is predictive of subsequent cognitive decline.

BackgroundThe brainstem locus coeruleus (LC) constitutes the intersection of the initial pathophysiological processes of Alzheimer’s disease (AD) and sleep-wake dysregulation in the preclinical stages of the disease. However, the interplay between in vivo assessment of LC degeneration and AD-related sleep alterations remains unknown. Here, we sought to investigate whether MRI-assessed LC structural integrity relates to subjective sleep-wake measures in the context of AD plasma biomarkers, in cognitively unimpaired older individuals.MethodsSeventy-two cognitively unimpaired older individuals aged 50–85 years (mean age = 65.2 ± 8.2 years, 37 women, 21APOEε4 carriers) underwent high-resolution imaging of the LC at 7 Tesla, and LC structural integrity was quantified using a data-driven approach. Reports on habitual sleep quality and nocturnal awakenings were collected using sleep questionnaires. Plasma levels of total tau, p-tau181, Aβ40, and Aβ42were measured using single-molecule array technology.ResultsIntensity-based cluster analyses indicated two distinct LC segments, with one covering the middle-to-caudal LC and displaying lower intensity compared to the middle-to-rostral cluster (t70= −5.12,p< 0.0001). After correction for age, sex, depression, andAPOEstatus, lower MRI signal intensity within the middle-to-caudal LC was associated with a higher number of self-reported nocturnal awakenings (F1,63= 6.73,pFDR= 0.03). Furthermore, this association was mostly evident in individuals with elevated levels of total tau in the plasma (F1,61= 4.26,p= 0.04).ConclusionOur findings provide in vivo evidence that worse LC structural integrity is associated with more frequent nocturnal awakenings in the context of neurodegeneration, in cognitively unimpaired older individuals. These results support the critical role of the LC for sleep-wake regulation in the preclinical stages of AD and hold promises for the identification of at-risk populations for preventive interventions.

The development of in vivo imaging of the pathologic hallmark of Alzheimer disease (AD), beta-amyloid (A beta), altered the framing of its pathophysiology and formulation of inclusion criteria for clinical trials. Recent evidence suggests that in vivo measures of A beta deposition below a threshold indicative of A beta positivity carry critical information on future cognitive decline and accumulation of AD pathology, potentially already at a younger age. Here, we integrate the existing literature on histopathology of A beta and its convergence and divergence with in vivo A beta imaging. The evidence presented amounts to a reconceptualization, in which we advocate for a closer look into A beta accumulation rates in earlier life, the factors that promote accumulation, comparative studies with different markers of A beta, and longitudinal designs to elucidate when AD pathology rises and how it shifts from benign to malignant stages that ultimately define AD. These efforts open a new window of opportunity for disease-modifying interventions.

Background Cognitive impairment is a common non-motor symptom in Parkinson's disease. So far, the underlying pathophysiology remains unclear. Several alterations in functional network connectivity have been described in Parkinson's disease patients with cognitive impairment which are probably the result of the heterogenous pathophysiology underlying this cognitive decline, including dopaminergic and cholinergic deficits. Accordingly, the reported resting-state connectivity patterns vary greatly among studies. Objective To evaluate the localization and magnitude of functional connectivity patterns in resting-state brain networks in Parkinson's disease patients with cognitive impairment by pooling data from available studies. Methods We searched PubMed, the Cochrane Library, MEDLINE, Embase and PsycINFO to identify functional MRI studies in Parkinson's disease patients with cognitive impairment. A voxel-based meta-analysis combined with quality statistics was performed, using the anisotropic effect-size version of the signed differential mapping method. Results Seventeen studies with cognitively impaired Parkinson's disease patients were included consisting of 222 Parkinson's disease patients with mild cognitive impairment, 68 patients with Parkinson's disease dementia, 289 cognitively unimpaired Parkinson's disease patients and 353 healthy controls. Parkinson's disease patients with cognitive impairment predominantly showed a reduced connectivity in specific brain regions that are part of the default mode network. Conclusion Cognitive impairment in Parkinson's disease is associated with reduced connectivity in networks relevant to cognition, most prominently the default mode network. Specific alterations in functional connectivity may contribute to cognitive decline in Parkinson patients and may be a promising future biomarker.

Background and Purpose— Cerebral amyloid angiopathy (CAA) is a common small vessel disease that independently effects cognition in older individuals. The pathophysiology of CAA and CAA-related bleeding remains poorly understood. In this postmortem study, we explored whether blood-brain barrier leakage is associated with CAA and microvascular lesions. Methods— Eleven CAA cases (median [IQR] age=69 years [65–79 years], 8 males) and 7 cases without neurological disease or brain lesions (median [IQR] age=77 years [68–92 years], 4 males) were analyzed. Cortical sections were sampled from each lobe, and IgG and fibrin extravasation (markers of blood-brain barrier leakage) were assessed with immunohistochemistry. We hypothesized that IgG and fibrin extravasation would be increased in CAA cases compared with controls, that this would be more pronounced in parietooccipital brain regions compared with frontotemporal brain regions in parallel with the posterior predilection of CAA, and would be associated with CAA severity and number of cerebral microbleeds and cerebral microinfarcts counted on ex vivo magnetic resonance imaging of the intact brain hemisphere. Results— Our results demonstrated increased IgG positivity in the frontotemporal ( P =0.044) and parietooccipital ( P =0.001) cortex in CAA cases compared with controls. Within CAA cases, both fibrin and IgG positivity were increased in parietooccipital brain regions compared with frontotemporal brain regions ( P =0.005 and P =0.006, respectively). The percentage of positive vessels for fibrin and IgG was associated with the percentage of amyloid-β–positive vessels (Spearman ρ=0.71, P =0.015 and Spearman ρ=0.73, P =0.011, respectively). Moreover, the percentage of fibrin and IgG-positive vessels, but not amyloid-β–positive vessels, was associated with the number of cerebral microbleeds on magnetic resonance imaging (Spearman ρ=0.77, P =0.005 and Spearman ρ=0.70, P =0.017, respectively). Finally, we observed fibrin deposition in walls of vessels involved in cerebral microbleeds. Conclusions— Our results raise the possibility that blood-brain barrier leakage may be a contributory mechanism for CAA-related brain injury.

Introduction Cortical thinning is a marker of neurodegeneration in Alzheimer's disease (AD). We investigated the age‐related trajectory of cortical thickness across the lifespan (9‐59 years) in a Colombian kindred with autosomal dominant AD (ADAD). Methods Two hundred eleven participants (105 presenilin‐1 [PSEN1] E280A mutation carriers, 16 with cognitive impairment; 106 non‐carriers) underwent magnetic resonance imaging. A piecewise linear regression identified change‐points in the age‐related trajectory of cortical thickness in carriers and non‐carriers. Results Unimpaired carriers exhibited elevated cortical thickness compared to non‐carriers, and thickness more negatively correlated with age and cognition in carriers relative to non‐carriers. We found increased cortical thickness in child carriers, after which thickness steadied compared to non‐carriers prior to a rapid reduction in the decade leading up to the expected age at cognitive impairment in carriers. Discussion Findings suggest that cortical thickness may fluctuate across the ADAD lifespan, from early‐life increased thickness to atrophy proximal to clinical onset.

BackgroundNeuroimaging studies of autosomal dominant Alzheimer’s disease (ADAD) enable characterization of the trajectories of cerebral amyloid-β (Aβ) and tau accumulation in the decades prior to clinical symptom onset. Longitudinal rates of regional tau accumulation measured with positron emission tomography (PET) and their relationship with other biomarker and cognitive changes remain to be fully characterized in ADAD.MethodsFourteen ADAD mutation carriers (Presenilin-1E280A) and 15 age-matched non-carriers from the Colombian kindred underwent 2–3 sessions of Aβ (11C-Pittsburgh compound B) and tau (18F-flortaucipir) PET, structural magnetic resonance imaging, and neuropsychological evaluation over a 2–4-year follow-up period. Annualized rates of change for imaging and cognitive variables were compared between carriers and non-carriers, and relationships among baseline measurements and rates of change were assessed within carriers.ResultsLongitudinal measurements were consistent with a sequence of ADAD-related changes beginning with Aβ accumulation (16 years prior to expected symptom onset, EYO), followed by entorhinal cortex (EC) tau (9 EYO), neocortical tau (6 EYO), hippocampal atrophy (6 EYO), and cognitive decline (4 EYO). Rates of tau accumulation among carriers were most rapid in parietal neocortex (~ 9%/year). EC tau PET signal at baseline was a significant predictor of subsequent neocortical tau accumulation and cognitive decline within carriers.ConclusionsOur results are consistent with the sequence of biological changes in ADAD implied by cross-sectional studies and highlight the importance of EC tau as an early biomarker and a potential link between Aβ burden and neocortical tau accumulation in ADAD.

Background and purpose Primitive reflexes may reoccur in various neurodegenerative diseases. However, little is known about their structural and functional correlates in the human brain. Notably, the neural mechanisms underlying a positive palmomental reflex (PMR) are poorly understood. As recent studies link Alzheimer's disease (AD)-related primitive reflexes to a dysfunction of the corticostriatal motor circuit (CMC), we conducted the present study to investigate functional and structural correlates of a positive PMR. We hypothesized an involvement of frontostriatal structures and an impairment of the CMC. Methods Using whole-brain resting-state functional connectivity (FC), hypothesis and FC result-based probabilistic tractography, and voxel-based morphometry analyses, we compared two groups of AD patients with either positive (n = 12) or negative PMR (n = 12). Results No significant differences in grey matter volume or structural connectivity (SC) could be observed between the PMR-positive and PMR-negative groups. In contrast, the PMR-positive group showed a decreased seed-to-voxel FC between the bilateral supplementary motor area and parts of the right-hemispherical caudate nucleus and thalamus and a decreased region of interest (ROI)-to-ROI FC between the left putamen and the left superior frontal gyrus. Conclusion Data suggest that dysfunction of the CMC reflected by decreased FC underlies a positive PMR in patients with AD. The lack of significant grey matter or SC differences might reflect that changes in FC appear before changes in SC in the structures of the CMC and brain atrophy.

Objective The goal of this study was to examine sex differences in tau distribution across the brain of older adults, using positron emission tomography (PET), and investigate how these differences might associate with cognitive trajectories. Methods Participants were 343 clinically normal individuals (women, 58%; 73.8 [8.5] years) and 55 individuals with mild cognitive impairment (MCI; women, 38%; 76.9 [7.3] years) from the Harvard Aging Brain Study and the Alzheimer's Disease Neuroimaging Initiative. We examined(18)F-Flortaucipir (FTP)-positron emission tomography (PET) signal across 41 cortical and subcortical regions of interest (ROIs). Linear regression models estimated the effect of sex on FTP-signal for each ROI after adjusting for age and cohort. We also examined interactions between sex*A beta-PET positive / negative (+ / -) and sex*apolipoprotein epsilon 4 (APOE epsilon 4) status. Linear mixed models estimated the moderating effect of sex on the relationship between a composite of sex-differentiated tau ROIs and cognitive decline. Results Women showed significantly higher FTP-signals than men across multiple regions of the cortical mantle (p