Differential spatial working memory-related functional network reconfiguration in young and older adults.

Functional brain networks have preserved architectures in rest and task; nevertheless, previous work consistently demonstrated task-related brain functional reorganization. Efficient rest-to-task functional network reconfiguration is associated with better cognition in young adults. However, aging and cognitive load effects, as well as contributions of intra- and internetwork reconfiguration, remain unclear. We assessed age-related and load-dependent effects on global and network-specific functional reconfiguration between rest and a spatial working memory (SWM) task in young and older adults, then investigated associations between functional reconfiguration and SWM across loads and age groups. Overall, global and network-level functional reconfiguration between rest and task increased with age and load. Importantly, more efficient functional reconfiguration associated with better performance across age groups. However, older adults relied more on internetwork reconfiguration of higher cognitive and task-relevant networks. These reflect the consistent importance of efficient network updating despite recruitment of additional functional networks to offset reduction in neural resources and a change in brain functional topology in older adults. Our findings generalize the association between efficient functional reconfiguration and cognition to aging and demonstrate distinct brain functional reconfiguration patterns associated with SWM in aging, highlighting the importance of combining rest and task measures to study aging cognition.

Brain networks identified by functional connectivity (FC) have preserved architectures from rest to task and across task demands. Higher similarity, implying more efficient network reconfiguration, was associated with better cognition and task performance in young adults. To examine how it may be influenced by aging, we compared whole-brain and network-level FC similarities between resting-state and spatial working memory fMRI in young and older adults. At whole-brain level and higher order cognitive networks, older adults evidenced less efficient network reconfiguration from rest to task than young adults. Importantly, more efficient reconfiguration was associated with better accuracy. This relationship relied more on internetwork connections in older adults. Despite reduced neural resources compared to young, maintaining efficient network updating still contributes to better cognition at older age.

Plasma Neurofilament Light Relates to Divergent Default and Salience Network Connectivity in Alzheimer's Disease and Behavioral Variant Frontotemporal Dementia.

Background: Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) show differential vulnerability to large-scale brain functional networks. Plasma neurofilament light (NfL), a promising biomarker of neurodegeneration, has been linked in AD patients to glucose metabolism changes in AD-related regions. However, it is unknown whether plasma NfL would be similarly associated with disease-specific functional connectivity changes in AD and bvFTD. Objective: Our study examined the associations between plasma NfL and functional connectivity of the default mode and salience networks in patients with AD and bvFTD. Methods: Plasma NfL and neuroimaging data from patients with bvFTD (n = 16) and AD or mild cognitive impairment (n = 38; AD + MCI) were analyzed. Seed-based functional connectivity maps of key regions within the default mode and salience networks were obtained and associated with plasma NfL in these patients. RESULTS: We demonstrated divergent associations between NfL and functional connectivity in AD + MCI and bvFTD patients. Specifically, AD + MCI patients showed lower default mode network functional connectivity with higher plasma NfL, while bvFTD patients showed lower salience network functional connectivity with higher plasma NfL. Further, lower NfL-related default mode network connectivity in AD + MCI patients was associated with lower Montreal Cognitive Assessment scores and higher Clinical Dementia Rating sum-of-boxes scores, although NfL-related salience network connectivity in bvFTD patients was not associated with Neuropsychiatric Inventory Questionnaire scores. CONCLUSIONS: Our findings indicate that plasma NfL is differentially associated with brain functional connectivity changes in AD and bvFTD.

Predictors of post stroke cognitive impairment: VITATOPS cognition substudy.

INTRODUCTION: Post stroke cognitive impairment (PSCI) is a common complication of ischemic stroke. PSCI can involve different depending on clinical and stroke related characteristics. The aim of this study is to determine the factors associated with impairments in specific cognitive domains. METHODS: The Vitamins to Prevent Stroke (VITATOPS) trial is a large, multinational randomised controlled trial. In this substudy, consecutive patients admitted for ischaemic stroke or transient ischaemic attack (TIA) at a tertiary hospital in Singapore were included. PSCI was defined as impairment of any of the six cognitive subgroups - visuoconstruction, attention, verbal memory, language, visual memory and visuomotor function - that were assessed annually for up to five years. Univariate and multivariate Cox proportional hazard models were used to determine factors associated with impairments in each of these cognitive domains. RESULTS: A total of 736 patients were included in this study, of which 173 (23.5 %) developed cognitive impairment. Out of the six cognitive domains, the greatest proportion of patients had an impairment in visuoconstruction (26.4 %) followed by attention (19.8 %), verbal memory (18.3 %), language (17.5 %), visual memory (17.3 %) and visuomotor function (14.8 %). Patients with posterior circulation cerebral infarction (POCI) as the index stroke subtype had higher rates of cognitive impairment. Further subgroup analyses show that Indian race and advanced age were predictive of language impairment, whilst fewer years of education and POCI were predictive of verbal memory impairment. POCI was predictive of visual memory impairment, and advanced age and POCI were predictive of visuomotor function impairment. CONCLUSION: We identified visuoconstruction and attention domains to be the most affected in our Asian cohort of PSCI. Advanced age, lower levels of education, posterior circulation strokes and concomitant comorbidities such as peripheral artery disease are independent predictors of PSCI.

Clinical characteristics of pathological confirmed prodromal dementia with Lewy bodies.

INTRODUCTION: Misdiagnosis rate of Dementia with Lewy Bodies (DLB) remains high despite being second most common cause of neurodegenerative dementia. To date, understanding of clinical profile of pathologically confirmed prodromal DLB remains limited. The main objective of this study was to describe and compare it with pathologically confirmed Alzheimer's disease (AD). METHODS: We accessed the National Alzheimer's Coordinating Center database from 2005 to December 2022 data freeze and included 111 and 501 prodromal DLB and AD patients respectively. First visit data was analyzed. RESULTS: Clinician-determined memory impairment is common in prodromal DLB (>70%) but associated with higher risk for AD diagnosis (OR 0.355, p = 0.0003). DLB had a higher proportion of non-amnestic mild cognitive impairment (MCI) diagnoses but statistically insignificance in differentiating the two. Inattention (OR 2.273, p = 0.0015), and neuropsychiatric features, such as visual hallucinations (OR 11.98, p < 0.0001), depressed mood (OR1.709, p = 0.0292), apathy (1.824, p = 0.0345), and night/REM sleep behaviors, are associated with DLB diagnosis. Hallucinations are infrequent (7-11%). Motor symptoms, particularly gait disorders (OR 4.570, p < 0.001), falls (OR3.939, p = 0.0003), tremors (OR2.237, p = 0.0154), slowness (OR3.573, p < 0.0001), and parkinsonism signs (OR2.443, p < 0.0001), are common. 32% showed no parkinsonism during initial presentation. Neuropsychological examination revealed less impaired memory and language but impaired executive function in DLB. CONCLUSION: In clinical practice, it is important to note that memory symptoms although being higher risk associated with AD diagnosis, are prominent in prodromal DLB. Psychosis is infrequent, and non-amnestic MCI is not necessarily associated with higher risk of DLB diagnosis. A careful clinical approach is key to improve the diagnosis of prodromal DLB.

B-vitamin supplementation on mitigating post-stroke cognition and neuropsychiatric sequelae: A randomized controlled trial.

BACKGROUND AND PURPOSE: A third of stroke patients suffer from post-stroke cognitive decline, depressive symptoms, and anxiety symptoms. B-vitamin supplementation provides a possible safe and affordable treatment to mitigate post-stroke neuropsychiatric sequelae via reducing homocysteine levels. Our study aims to examine the effect of B-vitamin supplementation in the prevention of post-stroke cognitive decline, depressive symptoms, and anxiety symptoms. Our secondary aims were to investigate associations between baseline factors and the three outcomes. METHODS: Patients were recruited as part of a Singaporean substudy of a randomized controlled trial that examined the effect of B-vitamin supplementation on recurrent cardiovascular events. Cognitive decline, depressive symptoms, and anxiety symptoms were assessed with neuropsychological assessments and Hospital Anxiety and Depression Scale 6 monthly. Cox regression analyses were performed to determine treatment efficacy. Logistic regression used to examine factors associated with cognitive decline, depressive symptoms, and anxiety symptoms. RESULTS: A total of 707 were included in the analyses. Survival and hazards ratio analysis showed no treatment effect of B-vitamins on cognitive decline, depressive symptoms, and anxiety symptoms. Cognitive decline was only associated with age. Depressive symptoms were associated with large anterior cerebral infarcts and hyperlipidemia. CONCLUSIONS: Our study showed no benefit of supplementation with B-vitamins for post-stroke cognitive decline, depressive symptoms, or anxiety symptoms. Depressive symptoms were associated with larger anterior cerebral infarcts, which may be reflective of the disability associated with larger infarcts.

Clinical Manifestations of Early-Onset Dementia With Lewy Bodies Compared With Late-Onset Dementia With Lewy Bodies and Early-Onset Alzheimer Disease.

Importance: Early-onset dementia, presenting in individuals younger than 65 years, is a diagnosis with significant social and financial implications. The early-onset form of dementia with Lewy bodies (DLB) is poorly understood. Objective: To investigate clinical features that distinguish early-onset DLB (onset and diagnosis at age <65 years) from late-onset DLB (onset at age ≥65 years) and from early-onset Alzheimer disease (AD) dementia. Design, Setting, and Participants: This is a retrospective case-control study on patients with pathologically confirmed DLB or AD enrolled in the National Alzheimer's Coordinating Center database from January 2005 to July 2017. The National Alzheimer's Coordinating Center Uniform Data Set comprised deidentified data collected by Alzheimer disease centers in the United States. Of patients fulfilling criteria for all-cause dementia at enrollment (n = 1152), those who at post mortem received a pathological diagnosis of either AD (n = 848) or Lewy body disease (n = 218) were selected. Excluding 52 patients owing to missing data and 12 diagnosed with Parkinson disease dementia, remaining patients were classified by age of symptom onset into early-onset AD, early-onset DLB, and late-onset DLB subgroups. Data were analyzed from June to December 2018 and from November to December 2021. Exposures: Demographics, cognitive, behavioral, and motor features recorded at first clinic visit and neuropathological characteristics at autopsy were analyzed by disease subgroup. Main Outcomes and Measures: Concordance between initial etiologic diagnosis of dementia and final pathological diagnosis was assessed, as was time to death. Results: A total of 542 individuals were categorized as having early-onset AD (n = 363; mean [SD] age, 53.0 [5.8] years; 208 [57.3%] male), early-onset DLB (n = 32; mean [SD] age, 57.9 [3.2] years; 23 [71.9%] male), and late-onset DLB (n = 147; mean [SD] age, 73.5 [5.5] years; 103 [70.1%] male). Early-onset DLB was clinically misdiagnosed in 16 individuals (50%). Features that predicted a diagnosis of early-onset DLB over early-onset AD included visual hallucinations (15 [46.9%] vs 42 [11.6%]), slowness (23 [71.9%] vs 95 [26.2%]), apathy (23 [71.9%] vs 189 [52.1%]), and motor deterioration that preceded cognitive and behavioral symptoms (7 [21.9%] vs 6 [1.7%]). Late-onset DLB had more amnestic features, but this was accounted for by a higher proportion of neocortical neuritic plaques and diffuse plaques (frequent in 79 [53.7%] vs 8 [25%]) than seen in early-onset DLB. Conclusions and Relevance: This study found that early-onset DLB has clinical features that distinguish it from early-onset AD, whereas features of late-onset DLB are associated with a higher burden of AD copathology.

Assessment of small intestinal bacterial overgrowth in Alzheimer's disease.

There is great interest in crosstalk between the gastrointestinal and immune systems. Small intestinal bacterial overgrowth (SIBO) is a bowel disorder prevalent among patients with Parkinson's disease; SIBO treatment has been shown to modulate neurological inflammation, motor and cognitive outcomes there. However, to date, no link between Alzheimer's dementia and SIBO has been established. This pilot study sought to estimate the prevalence of SIBO in Alzheimer's dementia in the outpatient setting in Singapore General Hospital. It entailed performing a hydrogen breath test and objectively scoring gastrointestinal symptoms and their severity in 48 patients, comparing symptom scores and mean breath test values in those with mild to moderate Alzheimer's against age- and sex-matched controls that did not fulfill DSM-V criteria for probable Alzheimer's. Here, the prevalence of positive breath tests and symptoms of SIBO were no greater among Alzheimer's patients than in controls. This suggests that the gut microbiome changes and increased bowel inflammation seen in previous studies on Alzheimer's patients are likely effected through pathways other than SIBO, and are likely more complex than a mere increase in small bowel bacterial volume. Rather, future research could be directed along the lines of qualitative changes in small bowel microbiota, or pathologies in other parts of the gastrointestinal tract such as the colon or stomach, aspects which are not adequately captured by the hydrogen breath test. Keywords: Alzheimer's disease; dementia; gut-brain axis; small intestinal bacterial overgrowth; microbiome.

Distinct network topology in Alzheimer's disease and behavioral variant frontotemporal dementia.

BACKGROUND: Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) cause distinct atrophy and functional disruptions within two major intrinsic brain networks, namely the default network and the salience network, respectively. It remains unclear if inter-network relationships and whole-brain network topology are also altered and underpin cognitive and social-emotional functional deficits. METHODS: In total, 111 participants (50 AD, 14 bvFTD, and 47 age- and gender-matched healthy controls) underwent resting-state functional magnetic resonance imaging (fMRI) and neuropsychological assessments. Functional connectivity was derived among 144 brain regions of interest. Graph theoretical analysis was applied to characterize network integration, segregation, and module distinctiveness (degree centrality, nodal efficiency, within-module degree, and participation coefficient) in AD, bvFTD, and healthy participants. Group differences in graph theoretical measures and empirically derived network community structures, as well as the associations between these indices and cognitive performance and neuropsychiatric symptoms, were subject to general linear models, with age, gender, education, motion, and scanner type controlled. RESULTS: Our results suggested that AD had lower integration in the default and control networks, while bvFTD exhibited disrupted integration in the salience network. Interestingly, AD and bvFTD had the highest and lowest degree of integration in the thalamus, respectively. Such divergence in topological aberration was recapitulated in network segregation and module distinctiveness loss, with AD showing poorer modular structure between the default and control networks, and bvFTD having more fragmented modules in the salience network and subcortical regions. Importantly, aberrations in network topology were related to worse attention deficits and greater severity in neuropsychiatric symptoms across syndromes. CONCLUSIONS: Our findings underscore the reciprocal relationships between the default, control, and salience networks that may account for the cognitive decline and neuropsychiatric symptoms in dementia.

Frontotemporal dementia and COVID-19: Hypothesis generation and roadmap for future research.

The COVID-19 pandemic has caused tremendous suffering for patients with dementia and their caregivers. We conducted a survey to study the impact of the pandemic on patients with mild frontotemporal dementia (FTD). Our preliminary findings demonstrate that patients with FTD have significant worsening in behavior and social cognition, as well as suffer greater negative consequences from disruption to health-care services compared to patients with AD. The reduced ability to cope with sudden changes to social environments places patients with FTD at increased vulnerability to COVID-19 infection as well as to poorer clinical and social outcomes. Caregivers of FTD patients also demonstrate high burden during crisis situations. A proportion of patients with FTD benefitted from use of web-based interactive platforms. In this article, we outline the priority areas for research as well as a roadmap for future collaborative research to ensure greatest benefit for patients with FTD and their caregivers.

Medial Temporal Atrophy in Amyloid-Negative Amnestic Type Dementia Is Associated with High Cerebral White Matter Hyperintensity.

BACKGROUND: Non-amyloid mechanisms behind neurodegeneration and cognition impairment are unclear. Cerebrovascular disease (CVD) may play an important role in suspected non-Alzheimer's pathophysiology (SNAP), especially in Asia. OBJECTIVE: To examine the association between CVD and medial temporal lobe atrophy (MTA) in amyloid-ß negative patients with mild amnestic type dementia. METHODS: Thirty-six mild dementia patients with complete neuropsychological, cerebrospinal fluid (CSF) biomarker, and neuroimaging information were included. Only patients with clinically significant MTA were recruited. Patients were categorized based on their CSF Aß levels. Neuroimaging and neuropsychological variables were analyzed. RESULTS: Despite comparable MTA between Aß positive and negative patients, Aß-negative patients had significantly greater white matter hyperintensities (WMH; Total Fazekas Rating) than their Aß-positive counterparts (6.42 versus 4.19, p = 0.03). A larger proportion of Aß-negative patients also had severe and confluent WMH. Regression analyses controlling for baseline characteristics yielded consistent results. CONCLUSION: Our findings demonstrate that MTA is associated with greater CVD burden among Aß-negative patients with amnestic type dementia. CVD may be an important mechanism behind hippocampal atrophy. This has implications on clinical management strategies, where measures to reduce CVD may slow neurodegeneration and disease progression.

Regional White Matter Hyperintensity Influences Grey Matter Atrophy in Mild Cognitive Impairment.

The association between cerebrovascular disease pathology (measured by white matter hyperintensities, WMH) and brain atrophy in early Alzheimer's disease (AD) remain to be elucidated. Thus, we investigated how WMH influence neurodegeneration and cognition in prodromal and clinical AD. We examined 51 healthy controls, 35 subjects with mild cognitive impairment (MCI), and 30 AD patients. We tested how total and regional WMH is related to specific grey matter volume (GMV) reductions in MCI and AD compared to controls. Stepwise regression analysis was further performed to investigate the association of GMV and regional WMH volume with global cognition. We found that total WMH volume was highest in AD but showed the strongest association with lower GMV in MCI. Frontal and parietal WMH had the most extensive influence on GMV loss in MCI. Additionally, parietal lobe WMH volume (but not hippocampal atrophy) was significantly associated with global cognition in MCI while smaller hippocampal volume (but not WMH volume) was associated with lower global cognition in AD. Thus, although WMH volume was highest in AD subjects, it had a more pervasive influence on brain structure and cognitive impairment in MCI. Our study thus highlights the importance of early detection of cerebrovascular disease, as its intervention at the MCI stage might potentially slow down neurodegeneration.

Dyslexic Characteristics of Chinese-Speaking Semantic Variant of Primary Progressive Aphasia.

Reading disorder is a recognized feature in primary progressive aphasia (PPA). Surface dyslexia, characterized by regularization errors, is typically seen in the English-speaking semantic variant of PPA (svPPA). However, dyslexic characteristics of other languages, particularly logographical languages such as Chinese, remain sparse in the literature. This study aims to characterize and describe the dyslexic pattern in this group of patients by comparing an English-speaking svPPA group with a Chinese-speaking svPPA group. The authors hypothesized that Chinese-speaking individuals with svPPA would likely commit fewer surface dyslexic errors. By accessing the database of Singapore's National Neuroscience Institute and the National Alzheimer's Coordinating Center of the United States, the authors identified three Chinese-speaking and 18 English-speaking patients with svPPA, respectively, for comparison. The results suggest that, instead of surface dyslexia, svPPA in Chinese-speaking individuals is characterized by a profound deep dyslexic error. Based on current evidence suggesting the role of the temporal pole as a semantic convergence center, the authors conclude that this region also mediates and converges lexical-semantic significance in logographical languages.

Characteristics of Chinese-English bilingual dyslexia in right occipito-temporal lesion.

Current literature suggests that right hemisphere lesions produce predominant spatial-related dyslexic error in English speakers. However, little is known regarding such lesions in Chinese speakers. In this paper, we describe the dyslexic characteristics of a Chinese-English bilingual patient with a right posterior cortical lesion. He was found to have profound spatial-related errors during his English word reading, in both real and non-words. During Chinese word reading, there was significantly less error compared to English, probably due to the ideographic nature of the Chinese language. He was also found to commit phonological-like visual errors in English, characterized by error responses that were visually similar to the actual word. There was no significant difference in visual errors during English word reading compared with Chinese. In general, our patient's performance in both languages appears to be consistent with the current literature on right posterior hemisphere lesions. Additionally, his performance also likely suggests that the right posterior cortical region participates in the visual analysis of orthographical word representation, both in ideographical and alphabetic languages, at least from a bilingual perspective. Future studies should further examine the role of the right posterior region in initial visual analysis of both languages.

Hyperfamiliarity in Amnestic and Vascular Mild Cognitive Impairment.

OBJECTIVE: Hyperfamiliarity is a phenomenon where new stimuli are perceived as familiar. Previous studies have demonstrated familiarity disorder in mild cognitive impairment (MCI), but mostly from the perspective of a neuropsychological approach, and the exact correlation of MCI aetiologies with the phenomenon remains uncertain. Based on current evidence suggesting a frontal-subcortical pathway contributing to familiarity processing, we hypothesize that individuals with a vascular aetiology of MCI will likely suffer more familiarity deficits. This study aims to examine the real-life hyperfamiliarity symptoms in amnestic versus vascular MCI. METHODS: Informants of 11 amnestic and 9 vascular cognitive impairment patients were interviewed about the frequency of hyperfamiliarity symptoms in the previous month. MRI brain images of vascular cognitive impairment patients were analysed as well. RESULTS: Patients with vascular cognitive impairment with no dementia (VCIND) showed a significantly higher frequency of hyperfamiliarity for people but not places or objects. Within VCIND patients, overall basal ganglia hyperintensities, particularly in the putamen, were found to significantly correlate to hyperfamiliarity. CONCLUSIONS: Patients with VCIND suffer more real-life hyperfamiliarity during people recognition compared to patients with amnestic mild cognitive impairment (aMCI), despite a comparative global decline in cognitive. This is likely due to impaired memory retrieval and matching processes resulting from subcortical ischaemic lesions.

Characteristics of number transcoding errors of Chinese- versus English-speaking Alzheimer's disease patients.

Number processing disorder is an acquired deficit in mathematical skills commonly observed in Alzheimer's disease (AD), usually as a consequence of neurological dysfunction. Common impairments include syntactic errors (800012 instead of 8012) and intrusion errors (8 thousand and 12 instead of eight thousand and twelve) in number transcoding tasks. This study aimed to understand the characterization of AD-related number processing disorder within an alphabetic language (English) and ideographical language (Chinese), and to investigate the differences between alphabetic and ideographic language processing. Chinese-speaking AD patients were hypothesized to make significantly more intrusion errors than English-speaking ones, due to the ideographical nature of both Chinese characters and Arabic numbers. A simplified number transcoding test derived from EC301 battery was administered to AD patients. Chinese-speaking AD patients made significantly more intrusion errors (p = 0.001) than English speakers. This demonstrates that number processing in an alphabetic language such as English does not function in the same manner as in Chinese. The impaired inhibition capability likely contributes to such observations due to its competitive lexical representation in brain for Chinese speakers.