NeuroImage
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Different EEG-vigilance stages from full alertness to sleep onset can be separated during rest. Also fMRI research recently focused on the resting condition and identified several resting state networks. In order to deepen the understanding of different levels of global brain function from relaxed wakefulness to sleep onset the association between EEG-vigilance stages and BOLD signals was analysed. ⋯ Resting state networks revealed a spatial overlap with the vigilance stage associated BOLD maps in conjunction analyses. sLORETA showed increased neuroelectric alpha activity at the occipital cortex comparable to occipital BOLD signal decreases when comparing stage A with stage B. Different EEG-vigilance stages during rest are associated with pronounced differences of BOLD signals in several brain areas which partly correspond to the resting state networks. For cognitive fMRI-research it therefore seems important to pay attention to vigilance switches in order to separate vigilance associated BOLD signal changes from those specifically related to cognition.
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Comparative Study
Does diffusion kurtosis imaging lead to better neural tissue characterization? A rodent brain maturation study.
Diffusion kurtosis imaging (DKI) can be used to estimate excess kurtosis, which is a dimensionless measure for the deviation of water diffusion profile from Gaussian distribution. Several recent studies have applied DKI to probe the restricted water diffusion in biological tissues. The directional analysis has also been developed to obtain the directionally specific kurtosis. ⋯ Conventional diffusion tensor imaging (DTI) parameters were also computed using monoexponential model, yielding reduced sensitivity and directional specificity in monitoring the brain maturation changes. These results demonstrated that, by measuring directionally specific diffusivity and kurtosis, DKI offers a more comprehensive and sensitive detection of tissue microstructural changes. Such imaging advance can provide a better MR diffusion characterization of neural tissues, both WM and GM, in normal, developmental and pathological states.
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Previous studies have established regional gray matter (GM) volume loss in multiple sclerosis (MS) but the relationship between development of white matter (WM) lesions and changes of regional GM volumes is unclear. The present study addresses this issue by means of voxel-based morphometry (VBM). T1-weighted three-dimensional magnetic resonance imaging (MRI) data from MS patients followed up for 12 months were analyzed using VBM. ⋯ Within the RRMS group, those patients with increasing T2 and T1 lesion burden (n=45) showed additional GM volume loss during follow-up in the frontal and parietal cortex, and precuneus. In contrast, patients lacking an increase in WM lesion burden (n=44) did not show any significant GM changes. The present study suggests that the progression of regional GM volume reductions is associated with WM lesion progression and occurs predominantly in fronto-temporal cortical areas.
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Cortical spreading depression (i.e. waves of cellular depolarization, CSD) causes the aura symptoms in classical migraine, and may contribute to delayed cellular damage after an ischemic or traumatic insult to the brain. In the latter cases, secondary neuronal injury may be worsened by some of the cerebral blood flow (CBF) changes that are associated with CSD. Here, we describe a new method for the simultaneous, live imaging of local cellular depolarization and CBF changes (i.e. two variables with well-defined and important biological significance), through a closed cranial window prepared in anesthetized rats. ⋯ In addition to the high temporal and spatial resolution of VS dye and LSC imaging, their novel combination allows to determine how CBF changes relate to a heterogeneous and evolving pattern of cellular depolarization, in any area of interest of the cortical region under study. This methodological development is especially pertinent and timely for investigations into the peri-lesion depolarizations that occur in models of focal brain injury, situations where their site of spontaneous elicitation and propagation pattern cannot be predicted. It should also help advance our knowledge in epilepsy, CBF pharmacology, and neurovascular coupling under normal and pathophysiological conditions.
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According to meta-analyses, depression is associated with a smaller hippocampus. Most magnetic resonance imaging (MRI) studies among middle aged acute depressed patients are based on manual segmentation of the hippocampus. Few studies used automated methods such as voxel-based morphometry (VBM) or automated segmentation that can overcome certain drawbacks of manual segmentation (essentially intra- and inter-rater variability and operator time consumption). ⋯ Using VBM-DARTEL, when corrected for multiple comparisons, significant volume differences were detected between groups in different regions and more specifically in hippocampus with ROI analyses. Whereas using standard VBM (without DARTEL), ROI analyses did not show bilateral volume between group differences. Significant hippocampal volume reductions between patients and controls were also detected using manual segmentation (-11.6% volume reduction, p<0.05) and automated segmentation (-9.7% volume reduction, p<0.05). VBM-DARTEL and automated segmentation show equal sensitivity in detecting hippocampal differences in depressed patients, while standard VBM was unable to detect hippocampal changes. Both VBM-DARTEL and automated segmentation could be used to perform large scale volumetric studies in humans. The new automated segmentation technique could further explore and detect hippocampal subpart differences that could be very useful for clarifying physiopathology of psychiatric disorders.