Neuroscience
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Compared to isometric activities, the neural basis of fatigue induced by repetitive tasks has been scarcely studied. Recently, we showed that during short-lasting repetitive tasks at the maximal possible rate (finger tapping for 10 and 30s), tapping rate and maximal voluntary contraction (MVC) force decrease at the end of finger tapping. We also observed larger silent periods (SP) induced by transcranial magnetic stimulation during MVC post finger tapping. ⋯ While indices of excitability increased initially in both tasks, they decreased with the isometric task only when the task was prolonged to 30s. We suggest that the inability to maintain increased levels of spinal excitability during task execution is a neurophysiological mark of fatigue. Our results suggest that the origin of fatigue induced by brief and fast repetitive tasks is not spinal.
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We investigated hemispheric asymmetries in categorization of face gender by means of a divided visual field paradigm, in which female and male faces were presented unilaterally for 150ms each. A group of 60 healthy participants (30 males) and a male split-brain patient (D. D. ⋯ His performance was higher than expected by chance - and did not differ from controls - only for male faces presented in the LVF. The residual right-hemispheric ability of the split-brain patient in categorizing male faces reveals an own-gender bias lateralized in the right hemisphere, in line with the rightward own-identity and own-age bias previously shown in split-brain patients. The gender-contingent hemispheric dominance found in healthy participants confirms the previously shown right-hemispheric superiority in recognizing female faces, and also reveals a left-hemispheric superiority in recognizing male faces, adding an important evidence of hemispheric imbalance in the field of face and gender perception.
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Propofol is a major intravenous anesthetic that facilitates GABAA receptor-mediated inhibitory synaptic currents and modulates inward current (Ih), K(+), and voltage-gated Na(+) currents. This propofol-induced modulation of ionic currents changes intrinsic membrane properties and repetitive spike firing in cortical pyramidal neurons. However, it has been unknown whether propofol modulates these electrophysiological properties in GABAergic neurons, which express these ion channels at different levels. ⋯ Using a low concentration of propofol clarified this tendency: 30μM propofol decreased the firing of pyramidal neurons but had little effect on GABAergic neurons. Pre-application of a GABAA receptor antagonist, picrotoxin (100μM), diminished the propofol-induced suppression of neural activities in both pyramidal and FS neurons. These results suggest that GABAergic neurons, especially FS neurons, are less affected by propofol than are pyramidal neurons and that propofol-induced modulation of the intrinsic membrane properties and repetitive spike firing are principally mediated by GABAA receptor-mediated tonic currents.
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Experiments on the adult visual cortex of cats, ferrets and monkeys have revealed organized spatial relationships between multiple feature maps which can also be reproduced by the Kohonen and elastic net self-organization models. However, attempts to apply these models to simulate the temporal kinetics of monocular deprivation (MD) during the critical period, and their effects on the spatial arrangement of feature maps, have led to conflicting results. In this study, we performed MD and chronic imaging in the ferret visual cortex during the critical period of ocular dominance (OD) plasticity. ⋯ Relationships between OD and orientation maps remained similar but were significantly weakened due to OD border shifts. These results indicate that orthogonal gradient relationships between maps may be preset and are only mildly modifiable during the critical period. The Kohonen model was able to reproduce these experimental results, hence its role is further extended to the description of cortical feature map dynamics during development.
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Uric acid is a naturally occurring, endogenous compound that impacts mental health. In particular, uric acid levels are associated with emotion-related psychopathology (e.g., anxiety and depression). Therefore, understanding uric acid's impact on the brain would provide valuable new knowledge regarding neural mechanisms that mediate the relationship between uric acid and mental health. ⋯ Specifically, activity within the hippocampus and surrounding cortex increased as a function of uric acid level. The current findings suggest that uric acid levels modulate stress-related hippocampal activity. Given that the hippocampus has been implicated in emotion regulation during psychosocial stress, the present findings offer a potential mechanism by which uric acid impacts mental health.