NeuroImage
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Expectations shape the way we experience the world. In this study, we used fMRI to investigate how positive and negative expectation can change pain experiences in the same cohort of subjects. We first manipulated subjects' treatment expectation of the effectiveness of three inert creams, with one cream labeled "Lidocaine" (positive expectancy), one labeled "Capsaicin" (negative expectancy) and one labeled "Neutral" by surreptitiously decreasing, increasing, or not changing respectively, the intensity of the noxious stimuli administered following cream application. ⋯ No brain regions were identified as common to both "Capsaicin" and "Lidocaine" conditioning. There was also no significant association between the brain response to identical noxious stimuli in the pain matrix evoked by positive and negative expectancies. Our findings suggest that positive and negative expectancies engage different brain networks to modulate our pain experiences, but, overall, these distinct patterns of neural activation result in a correlated placebo and nocebo behavioral response.
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Emotionally arousing stimuli are known to rapidly draw the brain's processing resources, even when they are task-irrelevant. The steady-state visual evoked potential (SSVEP) response, a neural response to a flickering stimulus which effectively allows measurement of the processing resources devoted to that stimulus, has been used to examine this process of attentional shifting. Previous studies have used a task in which participants detected periods of coherent motion in flickering random dot kinematograms (RDKs) which generate an SSVEP, and found that task-irrelevant emotional stimuli withdraw more attentional resources from the task-relevant RDKs than task-irrelevant neutral stimuli. ⋯ In the present study, we used two different types of emotional distractors - IAPS pictures and facial expressions - for which emotional cue extraction occurs at different speeds, being typically earlier for faces (at ~170ms, as indexed by the N170) than for IAPS images (~220-280ms, EPN). We found that emotional modulation of attentional resources as measured by the SSVEP occurred earlier for faces (around 180ms) than for IAPS pictures (around 550ms), after the extraction of emotional cues as indexed by visual ERP components. This is consistent with emotion related re-allocation of attentional resources occurring after emotional cue extraction rather than being linked to a time-fixed shifting process.
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MR-based correction for photon attenuation in PET/MRI remains challenging, particularly for neurological applications requiring quantitation of data. Existing methods are either not sufficiently accurate or are limited by the computation time required. The goal of this study was to develop an MR-based attenuation correction method that accurately separates bone tissue from air and provides continuous-valued attenuation coefficients for bone. ⋯ We propose an MR-based attenuation correction method (CAR-RiDR) for quantitative PET neurological imaging. The proposed method employs UTE and Dixon images and consists of two novel components: 1) accurate segmentation of air and bone using the inverse of the UTE1 image and the R2* image, respectively and 2) estimation of continuous LAC values for bone using a regression between R2* and CT-Hounsfield units. From our analysis, we conclude that the proposed method closely approaches (<3% error) the gold standard CT-scaled method in PET reconstruction accuracy.
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Chronic hypertension alters cerebral vascular morphology, cerebral blood flow (CBF), cerebrovascular reactivity, and increses susceptibility to neurological disorders. This study evaluated: i) the lumen diameters of major cerebral and downstream arteries using magnetic resonance angiography, ii) basal CBF, and iii) cerebrovascular reactivity to hypercapnia of multiple brain regions using arterial-spin-labeling technique in spontaneously hypertensive rats (SHR) at different stages. Comparisons were made with age-matched normotensive Wistar Kyoto (WKY) rats. ⋯ We also found enlargement of downstream vessels and formation of collateral vessels as compensatory responses to stenosis of upstream vessels. The middle cerebral and azygos arteries were amongst the most susceptible to hypertension-induced changes. Multimodal MRI provides clinically relevant data that might be useful to characterize disease pathogenesis, stage disease progression, and monitor treatment effects in hypertension.
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Studies in adults indicate that white matter microstructure, assessed with diffusion tensor imaging (DTI), has high heritability. Little is known about genetic and environmental influences on DTI parameters, measured along fiber tracts particularly, in early childhood. In the present study, we report comprehensive heritability data of white matter microstructure fractional anisotropy (FA), radial diffusion (RD), and axial diffusion (AD) along 47 fiber tracts using the quantitative tractography in a large sample of neonatal twins (n=356). ⋯ In a single tract analysis, genetic influences along the length of the tract were highly variable. These findings suggest that at birth, there is marked heterogeneity of genetic influences of white matter microstructure within white matter tracts. This study provides a basis for future studies of developmental changes in genetic and environmental influences during early childhood, a period of rapid development that likely plays a major role in individual differences in white matter structure and function.