NeuroImage
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Brain-derived neurotrophic factor (BDNF) is involved in memory and the pathophysiology of various neuropsychiatric disorders. A single nucleotide polymorphism in the human BDNF gene (Val66Met) affects memory, and influences Alzheimer's disease and depression vulnerability in a sex-specific manner. Recent animal studies suggest that BDNF mediates memory for emotional experiences in the amygdala, but it is currently unknown whether BDNF Val66Met influences memory processing in the amygdala. ⋯ Subsequent tests showed a larger contribution of these brain regions to successful encoding and retrieval in male Met allele carriers than male Val homozygotes, whereas no significant differences were observed in females. These results provide preliminary evidence that the BDNF Val66Met polymorphism influences specific mnemonic operations underlying encoding and retrieval of salient stimuli, and suggest less efficient memory processing in male Met allele carriers. Furthermore, the sex-specific genotype effects may contribute to sex-specific effects of BDNF Val66Met on depression vulnerability.
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Generalized tonic-clonic seizures cause widespread physiological changes throughout the cerebral cortex and subcortical structures in the brain. Using combined blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) at 9.4 T and electroencephalography (EEG), these changes can be characterized with high spatiotemporal resolution. We studied BOLD changes in anesthetized Wistar rats during bicuculline-induced tonic-clonic seizures. ⋯ The largest ictal BOLD increases remained in the focal regions of somatosensory cortex showing pre-ictal increases. During the post-ictal period we observed widespread BOLD decreases. These findings support a model in which "generalized" tonic-clonic seizures begin with focal changes before electrographic seizure onset, which progress to non-uniform changes during seizures, possibly shedding light on the etiology and pathophysiology of similar seizures in humans.
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Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a wide phenotypic range, often affecting personality and communication. Previous voxel-based morphometry (VBM) studies of ASD have identified both gray- and white-matter volume changes. However, the cerebral cortex is a 2-D sheet with a highly folded and curved geometry, which VBM cannot directly measure. ⋯ The thickness-based diagnostic model generated by LMT included 7 structures. Relative to controls, children with ASD had decreased cortical thickness in the left and right pars triangularis, left medial orbitofrontal gyrus, left parahippocampal gyrus, and left frontal pole, and increased cortical thickness in the left caudal anterior cingulate and left precuneus. Overall, thickness-based classification outperformed volume-based classification across a variety of classification methods.
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Recently, functional magnetic resonance imaging (fMRI) activation has been detected in white matter, despite the widely-held belief that fMRI activation is restricted to gray matter. The objective of the current study was to determine whether the regions of white matter fMRI activation were structurally connected to the functional network in gray matter. To do this, we used fMRI-guided tractography to evaluate whether tracts connecting regions of gray matter fMRI activation were co-localized with white matter fMRI activation. ⋯ In addition, callosal activation had tracts to bilateral gray matter fMRI activation for 7/8 participants. The results confirmed that the activated regions of the corpus callosum were structurally connected to the functional network of gray matter regions involved in the task. These findings are an important step towards establishing the functional significance of white matter fMRI, and provide the foundation for future work combining white matter fMRI and DTI tractography to study brain connectivity.
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Neuroimaging investigations of self-processing have generally focused on the neural correlates of explicit self-reflection. However, very little is known about the neural basis of implicit self-related processes. We utilized the concept of self-schemas to construct a two-task fMRI study that elicited both implicit and explicit self-relevant processes. ⋯ In the explicit self-reference task, participants judged the self-descriptiveness of adjectives related to athletics or science. Implicit and explicit processing of self-relevant (schematic) material elicited activity in many of the same regions, including medial prefrontal cortex, posterior cingulate/precuneus, ventromedial prefrontal cortex, subgenual anterior cingulate, amygdala, and ventral striatum. We suggest that processing self-related material recruits similar neural networks regardless of whether the self-relevance is made explicit or not.