Neuroscience
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To study the development of orthographic sensitivity during elementary school, we recorded event-related brain potentials (ERPs) from 2nd and 4th grade children who were exposed to line drawing of object or animals upon which the correctly or incorrectly spelled name was superimposed. Stimulus-locked ERPs showed a modulation of a frontocentral negativity between 200 and 500ms which was larger for the 4th grade children but did not show an effect of correctness of spelling. This effect was followed by a pronounced positive shift which was only seen in the 4th grade children and which showed a modulation of spelling correctness. ⋯ Moreover, response-locked ERPs triggered to the children's button presses indicating orthographic (in)-correctness showed a succession of waves including the frontocentral error-related negativity and a subsequent negativity with a more posterior distribution. This latter negativity was generally larger for the 4th grade children. Only for the 4th grade children, this negativity was smaller for the false alarm trials suggesting a conscious registration of the error in these children.
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Several brain structures including the brainstem, the cerebellum and the frontal cortico-basal ganglia network, with the primary and premotor areas have been shown to participate in the functional organization of gait initiation and postural control in humans, but their respective roles remain poorly understood. The aim of this study was to better understand the role of the supplementary motor area (SMA) and posterior cerebellum in the gait initiation process. Gait initiation parameters were recorded in 22 controls both before and after continuous theta burst transcranial stimulation (cTBS) of the SMA and cerebellum, and were compared to sham stimulation, using a randomized double-blind design study. ⋯ Functional inhibition of the SMA led to a shortened APA phase duration with advanced and increased muscle activity; during execution, it also advanced muscle co-activation and decreased the duration of stance soleus activity. Cerebellar functional inhibition did not influence the APA phase duration and amplitude but increased muscle co-activation, it decreased execution duration and showed a trend to increase velocity, with increased swing soleus muscle duration and activity. The results suggest that the SMA contributes to both the timing and amplitude of the APAs with no influence on step execution and the posterior cerebellum in the coupling between the APAs and execution phases and leg muscle activity pattern during gait initiation.
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The periodontal ligament (PDL) includes several types of nerve endings, such as Aβ-, Aδ-, and C-fibers, which play critical roles in detecting the strength and direction of occlusal force. Previous studies have demonstrated that electrical stimulation of the PDL activates the somatosensory and insular cortices. However, the profile of cortical excitation in response to mechanical PDL stimulation mostly remains unknown. ⋯ A paired-pulse protocol of mechanical stimulation revealed that the amplitude of the second response was smaller than the first response, in accordance with the shorter interstimulus interval. Systemic application of morphine, a potent blocker of nociception, reduced the amplitude of the maximum excitation, particularly in S2/IOR compared to S1. These results suggest that S1 and S2/IOR are principally excited by mechanical and electrical stimulation, respectively, and that S2/IOR is involved in nociception processing.
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Few researchers have investigated the direction of commissural axon projections on the contralateral side of the vertebrate embryonic spinal cord, especially for comparison between its different regions. In this study, pCAGGS-GFP plasmid expression was limited to different regions of the chicken embryonic spinal cord (cervical, anterior limb, anterior thorax, posterior thorax and posterior limb) at E3 using in ovo electroporation with modified electrodes and optimal electroporation conditions. Then open-book technique was performed at E6 to analyze the direction of axon projections in different spinal cord regions. ⋯ The ratio of rostral and caudal projections was significantly different between the five investigated regions (P<0.05), except between the cervical region and the anterior limb (P>0.05). The projections were most likely to be rostral for the posterior limb followed by the posterior thorax, cervical region, anterior limb and anterior thorax. Our data for the direction of the commissural axon projections will be helpful in the future analyses of axon projection mechanisms and spinal cord-brain circuit formation.
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Functional imaging studies have implicated the hippocampus and parahippocampal gyrus in cue-guided spatial navigation, but also many other regions. Furthermore, little is known about de-activations that take place during performance of navigation tasks, something that is of interest given that the hippocampus is a component of the default mode network, which de-activates during attention-demanding tasks. In this study 22 healthy subjects underwent whole-brain functional Magnetic Resonance Imaging (fMRI) while they navigated toward a previously learned goal in a virtual reality environment. ⋯ De-activations were seen in the medial frontal cortex and other regions of the default mode network, but not in the posterior cingulate cortex/precuneus. The findings support the involvement of the hippocampus in cue-guided navigation, but suggest that its posterior regions are particularly important. Cue-guided spatial navigation is associated with de-activation in some but not all parts of the default mode network.