NeuroImage
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Brain activity during resting wakefulness is characterized by slow (<0.1Hz) fluctuations of blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals that are topographically organized in discrete functional connectivity networks (resting-state networks, RSNs). The present study aimed at revealing possible network-specific alcohol-induced changes in resting-state fMRI (RS-fMRI) signals. RS-fMRI was carried out on eight healthy subjects in four consecutive 6-min sessions, one before and three after a 0.7 g/kg dose of ethyl alcohol. ⋯ Other major RSN components, such as the default-mode, the fronto-parietal, the sensori-motor, the self-referential and the auditory components, did not exhibit alcohol-induced changes during the same time window. Alcohol-induced effects on the resting-state functional connectivity of the visual network observed in the present study demonstrate that the visual system is a selective and primary target of acute alcohol administration. The strong enhancement of spontaneous BOLD fluctuations in the primary visual cortex in an acute alcoholic state may impair the normal activation response to visual stimuli and affect visual perception.
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Therapeutic development in amyotrophic lateral sclerosis (ALS) is hampered by the lack of suitable biomarkers that might be sensitive to spatial and temporal patterns of neurodegeneration. Diffusion tensor imaging is a useful non-invasive tool that permits detection of microstructural tissue changes due, for example, to neurodegeneration. Even though the spinal cord bears the brunt of the disease process, diffusion tensor imaging has mainly been used to study white matter changes in the brain. ⋯ Radial diffusivity in the white matter of the cervical cord was significantly correlated with clinical measures of disease severity such as forced vital capacity (FVC % predicted, r=-0.69, p<0.01), average finger and foot tapping speed from all four limbs (r=-0.59, p<0.05), and ALSFRS-R (r=-0.55, p<0.05) in ALS patients. There were no significant differences in mean diffusivity or axial diffusivity in the cervical spinal cord, or in any diffusion tensor imaging parameters measured in the brainstem. Analysis of diffusion tensor imaging parameters from individual cervical segments as well as profile plots along the length of the cervical cord showed larger differences in fractional anisotropy and radial diffusivity at more distal cervical segments, providing evidence that supports the "dying-back" hypothesis of neurodegeneration in ALS.
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Increases in neuronal activity induce local increases in cerebral perfusion. However, our understanding of the processes underlying this neurovascular coupling remains incomplete and, particularly, how these vary across the brain. Recent work supports an important role for astrocytes in neurovascular coupling, in large part via activation of their metabotropic glutamate receptors (mGluR). ⋯ Following MPEP, a negative component of the BOLD and CBV responses became more apparent, suggesting that different mechanisms mediate vasodilatory and vasoconstrictory responses. Interestingly, under baseline conditions the quantitative relationship between fMRI and LFP responses in cortical and subcortical regions was markedly different. Our data indicate that coupling between neuronal and fMRI responses is neither empirically nor mechanistically consistent across the brain.
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Spinal cord injury (SCI) can be accompanied by chronic pain, the mechanisms for which are poorly understood. Here we report that magnetic resonance spectroscopy measurements from the brain, collected at 3T, and processed using wavelet-based feature extraction and classification algorithms, can identify biochemical changes that distinguish control subjects from subjects with SCI as well as subdividing the SCI group into those with and without chronic pain. The results from control subjects (n=10) were compared to those with SCI (n=10). ⋯ The spectroscopy data obtained from the prefrontal cortex and anterior cingulate cortex both distinguished between SCI subjects with chronic neuropathic pain and those without pain with a sensitivity and specificity of 1.0. In this study, where two underlying mechanisms co-exist (i.e. SCI and pain), the thalamic changes appear to be linked more strongly to SCI, while the anterior cingulate cortex and prefrontal cortex changes appear to be specifically linked to the presence of pain.
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Many forms of psychopathology and substance abuse problems are characterized by chronic ritualized forms of avoidance and escape behavior that are designed to control or modify external or internal (i.e., thoughts, emotions, bodily sensations) threats. In this functional magnetic resonance imaging investigation, we examined amygdala reactivity to threatening cues when avoidance responding consistently prevented contact with an upcoming aversive event (money loss). In addition, we examined escape responding that terminated immediate escalating money loss and approach responding that produced a future money gain. ⋯ The magnitude of amygdala responses within subjects was relatively similar to avoidance, escape and approach cues, but considerable between-subject differences were found. The heightened amygdala response to avoidance and escape cues observed within a subset of subjects suggests threat-related responses can be maintained even when aversive events are consistently avoided, which may account for the persistence of avoidance-coping in various clinical disorders. Further assessment of the relation between amygdala reactivity and avoidance-escape behavior may prove useful in identifying individuals with or at risk for neuropsychiatric disorders.