Neuroscience
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The reading of action verbs has been shown to activate motor areas, whereby sentence context may serve to either globally strengthen this activation or to selectively sharpen it. To investigate this issue, we manipulated the presence of manual actions and sentence context, assessing the level of corticospinal excitability by means of transcranial magnetic stimulation. We hypothesized that context would serve to sharpen the neural representation of the described actions in the motor cortex, reflected in context-specific modulation of corticospinal excitability. ⋯ The coil was positioned over the cortical representation of the right first dorsal interosseous (pointer finger). We observed a general increase of corticospinal excitability while reading both manual action and non-manual verbs in minimal context, whereas the modulation was action-specific in rich context: corticospinal excitability increased while reading manual verbs, but did not differ from baseline for non-manual verbs. These findings suggest that sentence context sharpens motor representations, activating the motor cortex when relevant and eliminating any residual motor activation when no action is present.
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Language is a remarkable cognitive ability that can be expressed through visual (written language) or auditory (spoken language) modalities. When visual characters and auditory speech convey conflicting information, individuals may selectively attend to either one of them. However, the dominant modality in such a competing situation and the neural mechanism underlying it are still unclear. ⋯ Results showed a prominent auditory dominance when audio-visual competition occurred. Specifically, higher accuracy (ACC), larger N400 amplitudes and more linkages in the posterior occipital-parietal areas were demonstrated in the auditory mismatch condition compared to that in the visual mismatch condition. Our research illustrates the superiority of the auditory speech over the visual characters, extending our understanding of the neural mechanisms of audio-visual competition in Chinese.
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A signature feature of the neocortex is the dense network of horizontal connections (HCs) through which pyramidal neurons (PNs) exchange "contextual" information. In primary visual cortex (V1), HCs are thought to facilitate boundary detection, a crucial operation for object recognition, but how HCs modulate PN responses to boundary cues within their classical receptive fields (CRF) remains unknown. ⋯ Using a detailed compartmental model, we then show that this boundary-detecting classical-contextual interaction function can be computed by NMDAR-dependent spatial synaptic interactions within PN dendrites - the site where classical and contextual inputs first converge in the cortex. In additional simulations, we show that local interneuron circuitry activated by HCs can powerfully leverage the nonlinear spatial computing capabilities of PN dendrites, providing the cortex with a highly flexible substrate for integration of classical and contextual information.
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Increasing neurophysiological studies had revealed that regional excitation-inhibition imbalance in the brain played a key role in the pathogenesis of migraine. This study aimed to explore the alterations in gamma-aminobutyric acid (GABA) and glutamate/glutamine complex (Glx) levels in the anterior cingulate gyrus (ACC) and medial prefrontal lobe (mPFC) of patients with migraine without aura (MWoA) and investigate the correlation between neurotransmitter levels and clinical indicators. A total of 28 patients with MWoA and 28 sex-, age-, and education level-matched healthy controls (HCs) underwent single-voxel proton magnetic resonance spectroscopy scanning at 3.0 Tesla. ⋯ Negative correlations between GABA+/Cr levels and attack frequency were found in the ACC and mPFC regions of patients. These results suggested that there might be a close relationship between ACC and mPFC GABAergic neurons abnormalities and the pathophysiological mechanisms of MWoA. It might be beneficial to targeted treatment for patients with MWoA.
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Although altered microstructure properties of white-matter tracts have been reported in children with attention-deficit/hyperactivity disorder (ADHD), findings from relatively few adult ADHD studies are inconsistent. This study aims to examine microstructural property over the whole brain in adults with ADHD and explore structural connectivities. Sixty-four medication-naïve adults with ADHD and 81 healthy adults received diffusion spectrum imaging. ⋯ Adults with ADHD had increased mGFA values in the segments located in the left frontal aslant tract, the right inferior longitudinal fasciculus, and the left perpendicular fasciculus, and reduced mGFA values in the segments located in the right superior longitudinal fasciculus (SLF) I, the left SLF II, the right frontostriatal tracts from dorsolateral prefrontal cortex and the ventrolateral prefrontal cortex, the right medial lemniscus, the right inferior thalamic radiation to the auditory cortex, and the callosal fibers. Additionally, the mGFA value of the right SLF I segment was associated with hyperactivity-impulsivity symptoms. Our findings suggest that white-matter tracts with altered microstructure properties are located within the attention networks, fronto-striato-thalamocortical regions, and those associated with attention and visual perception in adults with ADHD.