NeuroImage
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Task switching requires executive control processes that undergo age-related decline. Previous neuroimaging studies have identified age-related differences in brain activation associated with global switching effects (dual-task blocks versus single-task blocks), but age-related differences in activation during local switching effects (switch trials versus repeat trials, within blocks) have not been investigated. This experiment used functional magnetic resonance imaging (fMRI), and diffusion tensor imaging (DTI), to examine adult age differences in task switching across adjacent trials (i.e., local task switching). ⋯ Further, individual differences in cue-related functional connectivity shared a substantial portion of the age-related variability in the efficiency of target categorization response (drift rate). This age-related difference in functional connectivity, however, was independent of white matter integrity within task-relevant regions. These findings highlight the functional connectivity of frontoparietal activation as a potential source of age-related decline in executive control.
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Compared to standard spoiled gradient echo (SPGR)-methods, balanced steady-state free precession (bSSFP) provides quantitative magnetization transfer (qMT) images with increased resolution and high signal-to-noise ratio (SNR) in clinically feasible acquisition times. The aim of this study was to acquire 3D high-resolution qMT-data to create standardized qMT-values of many single brain structures that might serve as a baseline for the future characterization of pathologies of the brain. QMT parameters, such as the fractional pool size (F), exchange rate (kf) and relaxation times of the free pool (T1, T2) were assessed in a total of 12 white matter (WM) and 11 grey matter (GM) structures in 12 healthy volunteers with MT-sensitized bSSFP. ⋯ The observed differences from previous studies can partly be explained by the reduced partial volume effects. MT-sensitized bSSFP is an ideal candidate for qMT-analysis in the clinical routine as it provides high-resolution 3D qMT-data of even small brain structures in clinically feasible acquisition times. The present qMT-data can serve as a reference for the characterization of cerebral diseases.
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Beta amyloid plaques, neurofibrillary tangles, and impaired glucose metabolism are among the most prevalent pathological characteristics of Alzheimer's disease (AD). However, separate visualization of these three AD-related pathologies in living humans has not been conducted. Here, we show that positron emission tomography (PET) imaging using the three radiotracers (11)C-Pittsburgh compound B (PIB), 2-(1-{6-[(2-(18)F-fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene) malononitrile (FDDNP), and 2-[18F]fluoro-2-deoxy-d-glucose (FDG), in the same subjects, with and without AD, can provide valuable information on the pathological patterns of the distribution of tracers for amyloid plaque, neurofibrillary tangle, and glucose hypometabolism in AD. ⋯ We found that the hippocampal formation was the most significant brain region in the voxel mapping of FDDNP minus PIB in the same patients with AD. Voxel-based analysis of FDG-PET in the same subjects revealed that brain regions with glucose hypometabolism in patients with AD overlap with regions of high PIB binding. In conclusion, PET imaging using these three radiotracers in the same subjects may contribute toward developing and testing disease-modifying drugs targeting amyloid pathology, tau pathology, and/or energy metabolism.
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During voluntary motor acts, potential perturbations due to transient external forces are counteracted very quickly by short- and long-latency stretch reflexes (SLSR and LLSR, respectively). The LLSR, presumably linked to a transcortical loop, can be modulated by the subjects' intention. Here, we used combined TMS-EEG to study cortical mechanisms involved in this intention-related modulation both before and during the reaction to a mechanical perturbation. ⋯ Therefore, the cortical mechanisms involved in the intention-related LLSR modulation differ from those involved in the voluntary reaction. In addition, in response to a single-pulse TMS delivered during the expectation of the mechanical perturbation, the TMS-evoked N100 amplitude decreased when subjects intended to 'let-go', suggesting anticipatory decreased activity of intracortical inhibitory sensorimotor networks. Taken together, these results support the idea that anticipatory processes preset the sensorimotor cortex so as to adapt its early reaction to the perturbation relative to the subjects' intention.
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Randomized Controlled Trial
Determining the optimal level of smoothing in cortical thickness analysis: a hierarchical approach based on sequential statistical thresholding.
The extent of smoothing applied to cortical thickness maps critically influences sensitivity, anatomical precision and resolution of statistical change detection. Theoretically, it could be optimized by increasing the trade-off between vertex-wise sensitivity and specificity across several levels of smoothing. But to date neither parametric nor nonparametric methods are able to control the error at the vertex level if the null hypothesis is rejected after smoothing of cortical thickness maps. ⋯ The hierarchical method was further validated in a cross-sectional study comparing moderate Alzheimer's disease (AD) patients with healthy elderly subjects. Results suggest that the extent of cortical thinning reported in previous AD studies might be artificially inflated by the choice of inadequate smoothing. In these cases, interpretation should be based on the location of local maxima of suprathreshold regions rather than on the spatial extent of the detected signal in the statistical parametric map.