Journal of Alzheimer's disease : JAD
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Cumulative evidence of gray matter abnormalities in semantic dementia (SD) has been reported using voxel-based morphometry (VBM). However, these studies have not been reviewed quantitatively. To estimate gray matter changes in SD quantitatively, we systematically searched whole-brain VBM studies comparing SD patients with healthy controls in the PubMed, ISI Web of Science, and EMABSE databases from January 1990 to August 2011. ⋯ Gray matter volume reductions were found in bilateral fusiform and inferior temporal gyri, extending to the medial portion of the temporal lobes (including amygdala and parahippocampal gyri), left temporal pole, middle temporal gyrus, and caudate. No significant increase in gray matter volume was found. Our findings provide strong evidence of atrophy in bilateral temporal lobes with predominate impairment on the left side, parahippocampal gyrus/amygdala, and left caudate, representing the pathophysiology of SD.
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Cognitive reserve is invoked to explain the protective effects of education and cognitively-stimulating activities against all-cause dementia and Alzheimer's disease (AD). For non-native English speakers (n-NES), speaking English may be a cognitive activity associated with lower dementia risk. We hypothesized that n-NES have lower risk of incident dementia/AD and that educational level might modify this relationship. ⋯ Results were similar for AD. Stratification of education into three groups revealed increased risk of dementia for n-NES with ≥ 16 years of education (HR 3.97; 95% CI 1.62-9.75; p = 0.003). We conclude that n-NES status does not appear to have an independent protective effect against incident dementia/AD, and that n-NES status may contribute to risk of dementia in an education-dependent manner.
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The Inferior parietal cortex (IPC), including the intraparietal sulcus (IPS), angular gyrus (AG), and supramarginal gyrus (SG), plays an important role in episodic memory, and is considered to be one of the specific neuroimaging markers in predicting the conversion of mild cognitive impairment (MCI) to Alzheimer's disease (AD). However, it is still unclear whether the connectivity of the IPC is impaired in MCI patients. In the present study, we used resting state fMRI to examine the functional connectivity of the three subdivisions of the IPC in MCI patients after controlling the impact of regional grey matter atrophy. ⋯ In contrast to the healthy controls, it was found that in MCI patients: 1) AG connectivity was significantly reduced within the DMN; 2) IPS showed decreased connectivity with the right inferior frontal gyrus while showing increased connectivity with the left frontal regions within the ECN; and 3) SG displayed decreased connectivity with a distribution of regions including the frontal and parietal regions, and increased connectivity with some sub-cortical areas within the SN. Moreover, the connectivity within the three networks was correlated with episodic memory and general cognitive impairment in MCI patients. These results extend well beyond the DMN, and further suggest that MCI is associated with alteration of large-scale functional brain networks.
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The measurement of hippocampal volumes using MRI is a useful in-vivo biomarker for detection and monitoring of early Alzheimer's disease (AD), including during the amnestic mild cognitive impairment (a-MCI) stage. The pathology underlying AD has regionally selective effects within the hippocampus. As such, we predict that hippocampal subfields are more sensitive in discriminating prodromal AD (i.e., a-MCI) from cognitively normal controls than whole hippocampal volumes, and attempt to demonstrate this using a semi-automatic method that can accurately segment hippocampal subfields. ⋯ Whole hippocampal volumes significantly differed bilaterally (left: p = 0.028, right: p = 0.009). This pattern of atrophy in a-MCI is consistent with the topography of AD pathology observed in postmortem studies, and corrected left CA1 provided stronger discrimination than whole hippocampal volume (p = 0.03). These results suggest that semi-automatic segmentation of hippocampal subfields is efficient and may provide additional sensitivity beyond whole hippocampal volumes.
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The structural integrity of the cerebral white matter, including that of the white matter lesions (WML) and of the surrounding normal appearing white matter (NAWM), can be assessed with diffusion tensor imaging (DTI), which is suggested to be of added value in the explanation of cognitive dysfunction in cerebral small vessel disease (SVD). We investigated the value of DTI of NAWM and WML in addition to conventional magnetic resonance imaging (MRI) parameters in the variance of cognitive performance in subjects with SVD. 499 individuals with SVD, 50-85 years, without dementia, underwent MRI scanning, including a DTI sequence. Grey matter, white matter (WM), and WML volume, number of microbleeds, lacunar and territorial infracts, and mean diffusivity (MD) and fractional anisotropy (FA) in NAWM, WML, and total WM were related to cognitive performance in multivariate regression analyses, after adjustment for age, gender, and education. ⋯ Both mean MD and FA of the NAWM, WML, and total WM did not substantially contribute to the explained variance of cognitive function, to that already explained by conventional MRI parameters. When considered separately, the MD of the (NA)WM had the strongest association with cognitive performance. In conclusion, DTI of NAWM and WML has limited additional value to conventional MRI parameters in the etiological explanation of the variance in cognitive function among individuals with SVD.