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Cognitive reserve (CR) shows protective effects on cognitive function in older adults. Here, we focused on the effects of CR at the functional network level. We assessed in patients with amnestic mild cognitive impairment (aMCI) whether higher CR moderates the association between low internetwork cross-talk on memory performance. In 2 independent aMCI samples (n = 76 and 93) and healthy controls (HC, n = 36), CR was assessed via years of education and intelligence (IQ). We focused on the anti-correlation between the dorsal attention network (DAN) and an anterior and posterior default mode network (DMN), assessed via sliding time window analysis of resting-state functional magnetic resonance imaging (fMRI). The DMN-DAN anti-correlation was numerically but not significantly lower in aMCI compared to HC. However, in aMCI, lower anterior DMN-DAN anti-correlation was associated with lower memory performance. This association was moderated by CR proxies, where the association between the internetwork anti-correlation and memory performance was alleviated at higher levels of education or IQ. In conclusion, lower DAN-DMN cross-talk is associated with lower memory in aMCI, where such effects are buffered by higher CR. [ABSTRACT FROM AUTHOR]

Resting-state functional connectivity (FC) is altered in Alzheimer's disease (AD) but its predictive value for episodic memory impairment is debated. Here, we aimed to assess whether resting-state FC in core brain regions activated during memory-task functional magnetic resonance imaging is altered and predictive of memory performance in AD and amnestic mild cognitive impairment (aMCI). Twenty-three elderly cognitively healthy controls (HC), 76 aMCI subjects, and 19 AD dementia patients were included. We computed resting-state FC between 18 meta-analytically determined peak coordinates of brain activation during successful memory retrieval. Higher FC between the parahippocampus, parietal cortex, and the middle frontal gyrus was observed in both AD and mild cognitive impairment compared to HC (false-discovery rate—corrected p < 0.05). The increase in FC between the parahippocampus and middle frontal gyrus was associated with reduced episodic memory in aMCI, independent of amyloid-beta positron emission tomography binding and apolipoprotein E ε4-carrier status. In conclusion, increased parahippocampal-prefrontal FC is predictive of impaired episodic memory in aMCI and may reflect a dysfunctional change within the episodic memory–related neural network. [ABSTRACT FROM AUTHOR]

In a recent postmortem study, R 2 * relaxometry in gray matter (GM) of the brain has been validated as a noninvasive measure for iron content in brain tissue. Iron accumulation in the normal aging brain is a common finding and relates to brain maturation and degeneration. The goal of this study was to assess the determinants of iron accumulation during brain aging. The study cohort consisted of 314 healthy community-dwelling participants of the Austrian Stroke Prevention Study. Their age ranged from 38–82 years. Quantitative magnetic resonance imaging was performed on 3T and included R 2 * mapping, based on a 3D multi-echo gradient echo sequence. The median of R 2 * values was measured in all GM regions, which were segmented automatically using FreeSurfer. We investigated 25 possible determinants for cerebral iron deposition. These included demographics, brain volume, lifestyle factors, cerebrovascular risk factors, serum levels of iron, and single nucleotide polymorphisms related to iron regulating genes (rs1800562, rs3811647, rs1799945, and rs1049296). The body mass index (BMI) was significantly related to R 2 * in 15/32 analyzed brain regions with the strongest correlations found in the amygdala ( p = 0.0091), medial temporal lobe ( p = 0.0002), and hippocampus ( p ≤ 0.0001). Further associations to R 2 * values were found in deep GM for age and smoking. No significant associations were found for gender, GM volume, serum levels of iron, or iron-associated genetic polymorphisms. In conclusion, besides age, the BMI and smoking are the only significant determinants of brain iron accumulation in normally aging subjects. Smoking relates to iron deposition in the basal ganglia, whereas higher BMI is associated with iron content in the neocortex following an Alzheimer-like distribution. [ABSTRACT FROM AUTHOR]

Gray matter (GM) atrophy and brain glucose hypometabolism are already detected in the predementia stages of Alzheimer's disease (AD), but the regional and longitudinal associations between the two are not well understood. Here, we analyzed the patterns of longitudinal atrophy (magnetic resonance imaging [MRI]) and 18 F-Fluorodeoxyglucose–positron emission tomography ([18F]FDG-PET) metabolism decline in 40 cognitively healthy control (HC) and 52 mildly impaired (mild cognitive impairment [MCI]) subjects during 3 years. Based on cerebrospinal fluid and brain amyloid-PET, the subjects were divided into amyloid-beta (Aβ)− and Aβ+ subgroups. In voxel-based and region of interest analyses, we compared the 3-year rates of change in GM and glucose metabolism between Aβ-subgroups, within each diagnostic group. In joint–independent component analyses, we assessed the patterns of covariation between longitudinal change in GM volume and glucose metabolism. MCI-Aβ+ showed faster atrophy than MCI-Aβ− within the temporal, medial temporal, and medial parietal lobes. HC-Aβ+ showed faster atrophy within the precuneus than HC-Aβ−. For FDG-PET metabolism, MCI-Aβ+ exhibited faster decline than MCI-Aβ− in temporoparietal regions, whereas no differences between HC subgroups were observed. Joint–independent component analysis showed that accelerated atrophy and metabolism decline correlated across distant brain regions for MCI-Aβ+. In conclusion, abnormally increased levels of Aβ in nondemented subjects were associated with accelerated decline in both GM and glucose metabolism, where both types of neurodegeneration progress in spatially divergent patterns. [ABSTRACT FROM AUTHOR]

Brain iron accumulates during aging and has been associated with neurodegenerative disorders including Alzheimer's disease. Magnetic resonance (MR)–based R2* mapping enables the in vivo detection of iron content in brain tissue. We investigated if during normal brain aging iron load relates to cognitive impairment in region-specific patterns in a community-dwelling cohort of 336 healthy, middle aged, and older adults from the Austrian Stroke Prevention Family Study. MR imaging and R2* mapping in the basal ganglia and neocortex were done at 3T. Comprehensive neuropsychological testing assessed memory, executive function, and psychomotor speed. We found the highest iron concentration in the globus pallidus, and pallidal and putaminal iron was significantly and inversely associated with cognitive performance in all cognitive domains, except memory. These associations were iron load dependent. Vascular brain lesions and brain volume did not mediate the relationship between iron and cognitive performance. We conclude that higher R2*-determined iron in the basal ganglia correlates with cognitive impairment during brain aging independent of concomitant brain abnormalities. The prognostic significance of this finding needs to be determined. [ABSTRACT FROM AUTHOR]

Abstract: A clinical impact of cognitive reserve (CR) has been demonstrated in Alzheimer''s disease, whereas its role in vascular cognitive impairment (VCI) is largely unknown. In this study, we investigated the impact of CR in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a genetic variant of pure VCI. A total of 247 NOTCH3 mutation carriers from a two-center study were investigated using detailed neuropsychological and neuroimaging protocols. CR was operationalized as years of formal education. Brain pathology was assessed by MRI using normalized brain volume and lacunar lesion volume as proxies. Multivariate analyses were done for each structural measure with scores of processing speed, executive function, and memory as dependent variables. Additional linear regression models were conducted with interaction terms for education × brain volume and education × lacunar lesion volume. Education had an independent impact on cognitive performance in subjects with mild and moderate degrees of brain pathology, whereas there was no significant influence of education on cognition in patients with severe MRI changes. This interaction was found for processing speed, the cognitive domain most impaired in our patients. Our findings demonstrate an interaction of education and brain pathology in regard to cognitive impairment: the effect of education seems most pronounced in early disease stages but may ultimately be overwhelmed by the pathological changes. The results extend the concept of CR to VCI. [Copyright &y& Elsevier]

Abstract: CADASIL is an arteriopathy caused by mutations of the Notch3 gene. White matter hyperintensities (WMH), lacunar lesions (LL), cerebral microhemorrhages (CM), brain atrophy and tissue microstructural changes are detected on MRI. Using an integrated multi-modal approach, we examined the relative impact of lesion burden and location of these MRI markers on cognitive impairment and disability. Multi-modal imaging was performed on 147 patients from a two-center cohort study. Volume of LL, WMH and number of CM was determined. Whole brain mean apparent diffusion coefficient (mean-ADC) and brain parenchymal fraction (BPF) were measured. In multivariate models accounting for lesion burden and location, volume of LL, mean-ADC, and BPF each had an independent influence on global cognitive function and disability. BPF explained the largest portion of the variation in cognitive and disability scores (35–38%). Brain atrophy has the strongest independent influence on clinical impairment in CADASIL when all MRI markers in the disease are considered together. The results suggest that the clinical impact of cerebral tissue loss plays a principal role in this genetic model of subcortical ischemic vascular dementia. [Copyright &y& Elsevier]

Abstract: Recent evidence suggests that hippocampal changes are present in vascular cognitive impairment but their importance and relationship with ischaemic mechanisms remain controversial. To investigate these issues we performed MRI and cognitive assessment in a large cohort (n =144) of patients with CADASIL, a hereditary small vessel disease and model of pure vascular cognitive impairment. Dementia status was ascribed according to DSM-IV and global cognitive function assessed with the Minimental State Examination (MMSE) and Mattis Dementia Rating Scale (MDRS). Hippocampal volume (HV) correlated with age (r =−0.33, p <0.001), brain volume (r =0.39, p <0.001) and lacunar lesion volume (r =−0.23, p =0.008), but not white matter lesions or microhaemorrhages. HV was reduced in dementia (2272±333mm3 versus 2642±349mm3, p <0.001) in the whole cohort and the subgroup progressing to dementia before age 60. HV correlated with MMSE (r =0.30, p <0.001), MDRS (r =0.40, p <0.001) and in a multivariate model predicted cognition independent of typical vascular lesions and whole brain atrophy. These findings strengthen the view that hippocampal atrophy is an important pathway of cognitive impairment in vascular as well as degenerative disease. [Copyright &y& Elsevier]

Abstract: In CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leucoencephalopathy), a genetic model of subcortical ischemic vascular dementia (SIVD), clinical status was previously found related to cortex morphology. In the present report, alterations of cortex morphology and their links to clinical worsening were investigated in 190 CADASIL patients followed during 24.4 months. Linear models were used to test relationships between: (1) clinical worsening and changes of depth of cortical sulci and of cortical thickness; (2) alterations of cortical morphology and changes of volume of white matter hyperintensities (WMHv) and of lacunar lesions (LLv). Reduction of sulcal depth was independently associated with increased time to complete trail making test A and B (p < 0.0001 and p = 0.004) and that of cortical thickness to increased disability (modified Rankin''s scale, p = 0.008), while brain atrophy was only related to global cognitive worsening (Mattis dementia rating scale, p = 0.002). The impact of volume of lacunar lesions on cortical alterations was larger than that of volume of white matter hyperintensities. Cortical alterations, mainly related to lacunar lesions, evolve parallel to clinical worsening. These results further support the eventual role of cortical alterations in subcortical ischemic vascular dementia. [Copyright &y& Elsevier]