Human brain mapping
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Human brain mapping · Feb 2009
Functional connectivity of default mode network components: correlation, anticorrelation, and causality.
The default mode network (DMN), based in ventromedial prefrontal cortex (vmPFC) and posterior cingulate cortex (PCC), exhibits higher metabolic activity at rest than during performance of externally oriented cognitive tasks. Recent studies have suggested that competitive relationships between the DMN and various task-positive networks involved in task performance are intrinsically represented in the brain in the form of strong negative correlations (anticorrelations) between spontaneous fluctuations in these networks. Most neuroimaging studies characterize the DMN as a homogenous network, thus few have examined the differential contributions of DMN components to such competitive relationships. ⋯ Activity in vmPFC negatively predicted activity in parietal visual spatial and temporal attention networks, whereas activity in PCC negatively predicted activity in prefrontal-based motor control circuits. Granger causality analyses suggest that vmPFC and PCC exert greater influence on their anticorrelated networks than the other way around, suggesting that these two default mode nodes may directly modulate activity in task-positive networks. Thus, the two major nodes comprising the DMN are differentiated with respect to the specific brain systems with which they interact, suggesting greater heterogeneity within this network than is commonly appreciated.
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Human brain mapping · Feb 2009
Sex differences in brain activation to anticipated and experienced pain in the medial prefrontal cortex.
Previous studies on sex differences in neural responses to noxious stimuli yielded mixed results. Both increased and decreased brain activation in several brain areas in women as compared to men has been reported. The current event-related functional magnetic resonance imaging study used a parametric design with different levels of the intensity of electrical stimulation in order to investigate sex differences in brain activation during pain processing. ⋯ Pronounced sex differences in brain activation were found in response to stimulation below the detection threshold and for the most intense pain stimuli in the medial prefrontal cortex (MPFC). Under both the conditions, women showed stronger activation in a region of the pregenual MPFC, which has been implicated in introspective, self-focused information processing. The results suggest that women, as compared to men, show increased self-related attention during anticipation of pain and in response to intense pain.
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Human brain mapping · Jan 2009
Stimulus-contrast-induced biases in activation order reveal interaction between V1/V2 and human MT+.
The luminance contrast of a visual stimulus is known to modulate the response properties of areas V1 and the human MT complex (hMT+), but has not been shown to modulate interactions between these two areas. We examined the direction of information transfer between V1/V2 and hMT+ at different stimulus contrasts by measuring magnetoencephalographic (MEG) responses to moving and stationary stimuli presented centrally or peripherally. To determine the direction of information flow, the different response latencies among stimuli and hemispheres in V1/V2 was compared with those of hMT+. ⋯ Here, the response variances in hMT+ mimicked and trailed those of V1/V2 at high contrast, whereas the reverse was true at low contrast. Such consistent interactions found using two different methodologies strongly supports a processing link between these two areas. The results also suggest that feedback from hMT+ for low-contrast stimuli compensates for unresolved processing in V1/V2 when the input of a visual image is weak.
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Human brain mapping · Jan 2009
Tactile-associated fMRI recruitment of the cervical cord in healthy subjects.
Using spinal cord functional magnetic resonance imaging (fMRI), 12 right-handed healthy subjects were scanned during a tactile stimulation of the palm of the right hand. The task-related mean signal change was computed for all activated voxels within the cervical cord, and separately, in the four cord quadrants (right and left anterior, right and left posterior) from C5 to C8. The frequency of fMRI activity at each cord level was obtained by assigning a score of 25% at each active quadrant and by averaging the percentage of active quadrants at each level of all subjects. ⋯ A significant heterogeneity in frequency of fMRI activity between cord levels was also observed (P < 0.001), with the highest frequencies of fMRI activity detected at C6 and C7. Spinal cord fMRI enables to obtain reliable physiological information on the activity of human spinal circuits associated to tactile stimulation. This holds significant promise for a better planning and conduct of studies of people with diseased spinal cords.
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Early visual deprivation may lead to both abnormal and plastic changes in the visual and other systems of the brain. Such secondary changes in the gray matter of the early blind have been well studied, but not so well in the cerebral white matter whose subtle changes may be revealed by diffusion tensor imaging. The first purpose of this study is to explore the possible changed white matter regions of the early blind in whole brain manners, using voxel-based analysis (VBA) and tract-based spatial statistics (TBSS) methods. ⋯ We found the early blind had significantly lower FA (P < 0.0001), higher MD (P = 0.001) and lambda(23) (P < 0.0001) in the GCT. This pattern of diffusion changes is similar to findings seen in immaturity or axonal degeneration. Thus, we suggest that transneuronal degeneration and/or immaturity may account for the abnormal diffusion changes in the GCT of the early blind.