NeuroImage
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The emergence of functional neuroimaging has dramatically accelerated our understanding of the human mind. The advent of functional Magnetic Resonance Imaging paved the way for the next decades' major discoveries in neuroscience and today remains the "gold standard" for deep brain imaging. Recent improvements in imaging technology have been somewhat limited to incremental innovations of mature techniques instead of breakthroughs. ⋯ The combination of many advantages, including high spatio-temporal resolution, deep penetration, high sensitivity and portability provided unique information about brain function. Recently, Ultrafast Doppler imaging was found able to non-invasively image the spatial and temporal dynamics of microvascular changes during seizures and interictal periods with an unprecedented resolution at bedside. This review summarizes the technical basis, the added value and the clinical perspectives provided by this new brain imaging modality that could create a breakthrough in the knowledge of brain hemodynamics, brain insult, and neuroprotection.
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Review
Can brain state be manipulated to emphasize individual differences in functional connectivity?
While neuroimaging studies typically collapse data from many subjects, brain functional organization varies between individuals, and characterizing this variability is crucial for relating brain activity to behavioral phenotypes. Rest has become the default state for probing individual differences, chiefly because it is easy to acquire and a supposed neutral backdrop. ⋯ Depending on the trait or behavior under study, certain tasks may bring out meaningful idiosyncrasies across subjects, essentially enhancing the individual signal in networks of interest beyond what can be measured at rest. Here, we review theoretical considerations and existing work on how brain state influences individual differences in functional connectivity, present some preliminary analyses of within- and between-subject variability across conditions using data from the Human Connectome Project, and outline questions for future study.
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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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Review
Magnetic Resonance Spectroscopy as a tool to study the role of GABA in motor-cortical plasticity.
Quantification of a number of neurochemicals within localised regions of tissue has long been possible using Magnetic Resonance Spectroscopy (MRS). In recent years, MRS has increasingly been utilised as a method to indirectly assess neuronal activity in vivo, primarily via measurement of the major neurotransmitters glutamate and γ-aminobutyric acid (GABA). To date a number of studies have highlighted relationships between local GABA levels and behaviour, and have demonstrated the modulation of GABA by protocols designed to induce synaptic plasticity. This review aims to examine the literature on MRS-assessed GABA changes in synaptic plasticity, focussing on the primary motor cortex (M1), to relate these to animal studies on the role of GABA in synaptic plasticity, and to highlight some of the important outstanding questions in interpreting MRS findings.
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Functional near-infrared spectroscopy (fNIRS) has now become widely accepted as a common functional imaging modality. In order for fNIRS to achieve genuine neuroimaging citizenship, it would ideally be equipped with functional and structural image analyses. However, fNIRS measures cortical activities from the head surface without anatomical information of the object being measured. ⋯ Eighth, we provide practical guidance on how these techniques are implemented in software. Finally, we provide information on current resources and limitations for spatial registration of child and infant data. Through these technical descriptions, we stress the importance of presenting fNIRS data on a common platform to facilitate both intra- and inter-modal data sharing among the neuroimaging community.