NeuroImage
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In addition to the BOLD scan, quantitative functional MRI studies require measurement of both cerebral blood volume (CBV) and flow (CBF) dynamics. The ability to detect CBV and CBF responses in a single additional scan would shorten the total scan time and reduce temporal variations. Several approaches for simultaneous CBV and CBF measurement during functional MRI experiments have been proposed in two-dimensional (2D) mode covering one to three slices in one repetition time (TR). ⋯ We estimated this using Bloch simulations and demonstrate that the resulting 3D acquisition can detect activation patterns and relative signal changes of quality comparable to that of the original separate scans. The same was found for temporal signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). This approach provides improved acquisition efficiency when both CBV and CBF responses need to be monitored during a functional task.
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Diffusion tractography relies on complex mathematical models that provide anatomical information indirectly, and it needs to be validated. In humans, up to now, tractography has mainly been validated by qualitative comparison with data obtained from dissection. No quantitative comparison was possible because Magnetic Resonance Imaging (MRI) and dissection data are obtained in different reference spaces, and because fiber tracts are progressively destroyed by dissection. Here, we propose a novel method and software (FIBRASCAN) that allow accurate reconstruction of fiber tracts from dissection in MRI reference space. ⋯ This paper presents the robustness of a novel method, FIBRASCAN, for accurate reconstruction of fiber tracts from dissection in the ex vivo MR reference space. This is a major step toward quantitative comparison of MR tractography with dissection results.
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Review Comparative Study
The structural and functional connectivity of the posterior cingulate cortex: comparison between deterministic and probabilistic tractography for the investigation of structure-function relationships.
The default mode network (DMN) is one of the most studied resting-state networks, and is thought to be involved in the maintenance of consciousness within the alert human brain. Although many studies have examined the functional connectivity (FC) of the DMN, few have investigated its underlying structural connectivity (SC), or the relationship between the two. We investigated this question in fifteen healthy subjects, concentrating on connections to the precuneus/posterior cingulate cortex (PCC), commonly considered as the central node of the DMN. ⋯ The direct comparison of FC and SC indicated that pairs of nodes with stronger structural connections also had stronger functional connectivity, and that this was maintained with both tractography approaches. Whilst the definition of SC strength remains controversial, our results could be considered to provide some degree of validation for the measures of SC strength that we have used. Direct comparisons of SC and FC are necessary in order to understand the structural basis of functional connectivity, and to characterise and quantify the changes in the brain's functional architecture that occur as a result of normal physiology or pathology.
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Repetitive navigated transcranial magnetic stimulation (rTMS) is increasingly used for preoperative cortical language mapping. Unlike direct cortical stimulation (DCS), and due to its non-invasive character, this technique can provide a map of the distribution of human language in the healthy brain as well as a dysfunctional brain. Although functional magnetic resonance imaging (fMRI) studies have reported interhemispheric functional connectivity between language structures, the way in which the right hemisphere helps bring about language function remains only partially investigated. The present study therefore uses rTMS as a virtual lesion model to investigate the right hemisphere's contribution to language processing in the healthy human brain. ⋯ For the first time, the present study provides data on the right hemisphere's cortical regions causally related to single word production function (right opIFG, aSMG, pSMG, mSTG), and selectively in female brains (right pSTG), from a large sample of 50 healthy adult brains in a virtual-lesion design. Moreover, speech-motor control regions (right mPrG, vPrG, mPoG, vPoG) and cortical regions supporting language task performance (mMFG, pMFG) in the language-non-dominant right hemisphere are described.
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This study investigates how the interaction of different brain oscillations (particularly theta-gamma coupling) modulates the bottom-up and top-down processes during speech perception. We employed a speech perception paradigm that manipulated the congruency between a visually presented picture and an auditory stimulus and asked participants to judge whether they matched or mismatched. A group of children (mean age 10 years, 5 months) participated in this study and their electroencephalographic (EEG) data were recorded while performing the experimental task. ⋯ This indicates that a fast global processing strategy and a slow detailed processing strategy were differentially adopted in the match and mismatch conditions. This study provides new insight into the mechanisms of speech perception from the interaction of different oscillatory activities and provides neural evidence for theories of speech perception allowing for top-down feedback connections. Furthermore, it sheds light on children's speech perception development by showing a similar pattern of integration of bottom-up and top-down information during speech perception as previous studies have revealed in adults.