NeuroImage
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The diffusion properties of water are sensitive to microscopic changes in the white matter of multiple sclerosis (MS) patients. Typical MRI measures of disease burden in MS demonstrate modest to poor correlation with disability. Functional MRI and DTI-based fiber tracking were used to define the interhemispheric white matter pathway connecting bilateral supplementary motor areas (SMA) in 16 MS patients sand 16 control subjects. ⋯ Mean lambda(2) values were (0.500 +/- 0.047) x 10(-3) mm(2) s(-1) for patients and (0.454 +/- 0.027) x 10(-3) mm(2) s(-1) for controls (P < 0.001). In addition, the correlation between the Multiple Sclerosis Functional Composite (MSFC) and transverse diffusivity was -0.341 (P < 0.05). The component test of the MSFC most related to the SMA pathway studied with our MRI method (Nine-hole Peg Test) showed significant correlation with transverse diffusivity (r = 0.392, P < 0.02), indicating that probing functional pathways with MRI measures can lead to a better reflection of disease status.
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This study investigates the effect of awareness of stimulus contingencies on BOLD responses within the amygdala, the orbitofrontal, and the occipital cortex, and on differential skin conductance responses (SCRs) during fear conditioning. Of two geometric figures, the paired conditioned stimulus (CS+) predicted an electrical stimulus (unconditioned stimulus = UCS), whereas the unpaired conditioned stimulus (CS-) was not followed by the UCS. Awareness of stimulus contingencies was manipulated experimentally, creating an aware and an unaware group: a distracter figure and a working memory task were introduced to conceal the stimulus contingencies of the conditioning paradigm, hence preventing contingency detection in the unaware group. ⋯ Conversely, we observed enhanced responses of the amygdala, the orbitofrontal, and the occipital cortex to the CS+ in the unaware group only. Thus, we found a dissociation of SCR differentiation and the activation of a neural fear network depending on the presence or absence of awareness. These results support a model of fear conditioning that distinguishes between a more cognitive level of learning, reflected in contingency awareness and differential SCRs, and the awareness independent activation of a fear network.
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The present study used functional magnetic resonance imaging to examine cortical specialization for letter processing. We assessed whether brain regions that were involved in letter processing exhibited domain-specific and/or mandatory responses, following Fodor's definition of properties of modular systems (Fodor, J. A., 1983. ⋯ These regions likely subserve some linguistically oriented cognitive process that is unique to letters, such as grapheme-to-phoneme translation or retrieval of phonological codes for letter names. Hence, cortical specialization for letters emerged in the naming task in some peri-sylvian language related cortices, but not in occipito-temporal cortex. Given that the domain-specific response for letters in left peri-sylvian regions was only present in the naming task, these regions do not process letters in a mandatory fashion, but are instead modulated by the linguistic nature of the task.
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The signal intensity during the dynamic approach to the equilibrium state of longitudinal magnetization is a function of sequence parameters, such as repetition time and flip angle, and depends on tissue characteristics, including longitudinal relaxation time of stationary tissue and the rate of blood inflow. A method is presented to extract information from data acquired during the transient state prior to T1 equilibrium using echo-planar acquisitions in T2*-weighted functional magnetic resonance imaging (fMRI) experiments. A voxel in a single slice acquisition is assumed to contain either stationary tissue or large vessels with flowing blood. ⋯ Histogram analysis of T1 distributions for activated voxels in a visual paradigm demonstrated the distributions are centered at T1 values of gray matter with tails at both sides of the center due to partial voluming of gray matter with white matter and CSF respectively. The mean gray matter volume fraction in activated voxels was about 0.9. The results indicate that transient data sets can provide additional information that is useful for both localization and characterization of the functionally relevant BOLD response.
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Idiopathic generalized epilepsies (IGE) are a group of frequent age-related epilepsy syndromes. IGE are clinically characterized by generalized tonic-clonic, myoclonic and absence seizures. According to predominant seizure type and age of onset, IGE are divided in subsyndromes: childhood absence and juvenile absence epilepsy (AE), juvenile myoclonic epilepsy (JME) and generalized tonic-clonic seizures on awakening (GTCS). ⋯ Region of interest analysis showed increased GMC in the anterior portion of the thalamus in patients with absence seizures. Our results support subtle GMC abnormalities in patients with JME and AE when compared to controls. These findings suggest the existence of different patterns of cortical abnormalities in IGE subsyndromes.