NeuroImage
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Multiple system atrophy (MSA) is a neurodegenerative disease affecting basal ganglia, brainstem, cerebellum, and intermediolateral cell columns of the spinal cord. Clinically, a cerebellar (MSA-C) and a parkinsonian variant of MSA (MSA-P) are distinguished. We used voxel-based morphometry (VBM) and voxel-based relaxometry (VBR) in 48 MSA patients (32 MSA-C, 16 MSA-P) and 46 controls. ⋯ A correlation with disease duration and severity was detected only for some small cortical areas. Direct comparison of MSA-C and MSA-P showed differences only in infratentorial brain regions where structural abnormalities were more pronounced in MSA-C than in MSA-P. In MSA-C, there was a stronger reduction of gray matter in the basal parts of the cerebellum, of white matter in the brainstem and of the relaxation rate R2 in the cerebellum and brainstem.
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Diffusion tensor imaging (DTI) is used to study tissue composition and architecture in vivo. To increase the signal to noise ratio (SNR) of DTI contrasts, studies typically use more than the minimum of 6 diffusion weighting (DW) directions or acquire repeated observations of the same set of DW directions. Simulation-based studies have sought to optimize DTI acquisitions and suggest that increasing the directional resolution of a DTI dataset (i.e., the number of distinct directions) is preferable to repeating observations, in an equal scan time comparison. ⋯ As long as sampling orientations are well balanced, differences in DTI contrasts due to different DW schemes are shown to be small relative to intra-session variability. These differences are accentuated at low SNR, while minimized at high SNR. This result suggests that typical clinical studies, which use similar protocols but different well-balanced DW schemes, are readily comparable within the experimental precision.
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Changes of cortical and corticospinal excitability as a function of sleep deprivation have been studied, using EEG power maps and several TMS measures in 33 normal subjects before and after a 40-h sleep deprivation (SD). The effects of SD were independently assessed by subjective and EEG measures of sleepiness, the latter being represented in terms of cortical maps for different frequency bands. Short intracortical facilitation (SICF) and inhibition (SICI) were measured by the paired-pulse TMS technique with different inter-stimulus intervals. ⋯ TMS and EEG measures converge in indicating that SD has severe effects on both cortical and corticospinal excitability, as shown respectively by the increases of slow-frequency EEG power and MTs. The SICF enhancement in females and the results of the combined topographical analysis of EEG and TMS changes are coherent with the hypothesis that cortical TMS-evoked responses are higher as a consequence of a longer wakefulness. However, the lack of an increase in cortical excitability after prolonged wakefulness in males suggests some caution in the generalization of these effects, that deserve further investigation.
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Comparative Study
Neural correlates of perceptual difference between itching and pain: a human fMRI study.
It has been wondered why we can discriminate between itching and pain as different sensations. Several researchers have investigated neural mechanisms underlying their perceptual differences, and found that some C fibers and spinothalamic tract neurons had different sensitivity between itching and pain. These findings suggest that such differences in ascending pathways are partly associated with perceptual difference between itching and pain. ⋯ These findings demonstrate that the difference in the sensitivity of PCC, the posterior insula and the thalamus between itching and pain would be responsible for the perceptual difference between these sensations. The previous itching studies did not observe an activation of the secondary somatosensory cortex (S2) by itching. However, we observed that an activation of S2 by pain was not significantly different from that by itching, indicating that S2 was associated with not only pain but also itching.
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Diffusion-weighted imaging (DWI) has been proposed as a sensitive measure of disease severity capable of detecting subtle changes in gray matter and white matter brain compartments in patients with multiple sclerosis (MS). However, DWI has been applied to the study of MS clinical subtypes in only a few studies. The objective of this study was to demonstrate the validity of a novel, fully automated method for the calculation of quantitative DWI measures. ⋯ ENT (R2=0.28; p<0.0001) and GMF (R2=0.26; p<0.001) were best related with SP disease course. This study highlights the validity of DWI in discerning differences between NC and MS patients, as well as between different MS subtypes. ENT is a sensitive marker of overall brain damage that is strongly related to clinical impairment in patients with SP MS.