NeuroImage
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The effective connectivity networks among overlapped core regions recruited by motor execution (ME) and motor imagery (MI) were explored by means of conditional Granger causality and graph-theoretic method, based on functional magnetic resonance imaging (fMRI) data. Our results demonstrated more circuits of effective connectivity among the selected seed regions during right-hand performance than during left-hand performance, implying the influences of brain asymmetry of right-handedness on effective connectivity networks. ⋯ Furthermore, the In-Out degrees of information flow suggested left dorsal premotor cortex (PMd), inferior parietal lobule (IPL) and superior parietal lobule (SPL) as causal sources in ME/MI tasks, highlighting the dominant function of left PMd, IPL and SPL. These findings depicted the causal connectivity of motor related core regions in fronto-parietal circuit and might indicate the conversion of causal networks between ME and MI.
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White matter (WM) lesions are the classic pathological hallmarks of multiple sclerosis (MS). However, MRI-based WM lesion load shows relatively poor correlation with functional outcome, resulting in the "clinico-radiological paradox" of MS. Unlike lesion based measures, volumetric MRI assessment of brain atrophy shows a strong correlation with functional outcome, and the presence of early atrophy predicts a worse disease course. ⋯ We earlier reported another neurodegenerative feature in this model, the presence of deep gray matter T2 hypointensity in thalamic nuclei. Future studies utilizing this model will allow us to investigate key components of MRI detectable neurodegenerative feature development, their tissue correlations and associations with functional outcome measures. These studies are expected to pave the way to a better understanding of the substrate of disability in MS models.
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The insula plays a key role in brain processing of noxious and innocuous thermal stimuli. The anterior and the posterior portions of the insular cortex are involved in different ways in nociceptive and thermoceptive processing. Therefore, their stimulus-specific functional connectivity may also differ. ⋯ When statistically compared, during both noxious and innocuous stimulation, aINS was more strongly connected to PFC and to ACC than was pINS; pINS meanwhile was more strongly connected to S1 and to the primary motor cortex (M1). Interestingly, S2 was more strongly connected to aINS than to pINS during painful stimulation but not during innocuous thermal stimulation. We conclude that aINS is more strongly functionally connected to areas known for affective and cognitive processing, whereas pINS is more strongly connected with areas known for sensory-discriminative processing of noxious and somatosensory stimuli.
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The calibration of functional magnetic resonance imaging (fMRI) for the estimation of neuronal activation-induced changes in cerebral metabolic rate of oxygen (CMRO(2)) has been achieved through hypercapnic-induced iso-metabolic increases in cerebral blood flow (CBF). Hypercapnia (HC) has been traditionally implemented through alterations in the fixed inspired fractional concentrations of carbon dioxide (F(I)CO(2)) without otherwise controlling end-tidal partial pressures of carbon dioxide (P(ET)CO(2)) or oxygen (P(ET)O(2)). There are several shortcomings to the use of this manual HC method that may be improved by using precise targeting of P(ET)CO(2) while maintaining iso-oxia. ⋯ The variability of the calibration constant obtained under HOP (M(HOP)) was 0.3-0.5 that of the HCP one (M(HCP)). In addition, M-variances with precise gas targeting (M(HCP) and M(HOP)) were less than those reported in studies using traditional F(I)CO(2) and F(I)O(2) methods (M(HC) and M(HO), respectively). We conclude that precise controlled gas delivery markedly improves BOLD-calibration for fMRI studies of oxygen metabolism with both the HCP and the more precise HOP-alternative.
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Reliable detection of metabolic changes in the brain in vivo induced by chronic low back pain may provide improved understanding of neurophysiological mechanisms underlying the manifestation of chronic pain. In the present study, absolute concentrations of N-acetyl-aspartate (NAA), creatine (Cr), total choline (tCho), myo-inositol (mI), glutamate (Glu) and glutamine (Gln) were measured in three different pain processing cortical regions (anterior insula, anterior cingulate cortex, and thalamus) of ten patients with non-specific chronic low back pain by means of proton MR spectroscopy ((1)H-MRS) and compared to matched healthy controls. Significant decrease of Glu was observed in the anterior cingulate cortex of patients. ⋯ Reduced concentrations of Glu and Gln may indicate disordered glutamatergic neurotransmission due to prolonged pain perception, whereas decrease of NAA and mI may be ascribed to neuron and glial cell loss. No significant changes were found for Cr. The morphological evaluation of anatomic brain data revealed a significantly decreased WM volume of 17% (p<0.05) as well as a non significant trend for GM volume increase in the anterior insula of patients.