Neuroscience
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Short-term plasticity enables synaptic strength to be dynamically regulated by input timing. Excitatory synapses arising from the same axon can have profoundly different presynaptic forms of short-term plasticity onto inhibitory and excitatory neurons. We previously showed that Schaffer collateral synapses onto most hippocampal CA1 stratum radiatum interneurons have less paired-pulse facilitation than synapses onto CA1 pyramidal cells, but little difference in steady-state short-term depression. ⋯ These target-cell specific differences in short-term plasticity reduce the strength of excitatory input onto interneurons relative to pyramidal cells, and of depression interneurons relative to facilitation interneurons, during high frequency portions of the train. This occurs to a similar extent at 25 °C and at 33 °C, and is even greater at physiological extracellular calcium. Target-cell specific differences in short-term plasticity enable synapses to have different temporal filtering characteristics, which may help to dynamically regulate the balance of inhibition and excitation in CA1.
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Changes in inhibition following traumatic brain injury (TBI) appear to be one of the major factors that contribute to excitation:inhibition imbalance. Neuron pathology, interneurons in particular evolves from minutes to weeks post injury and follows a complex time course. Previously, we showed that in the long-term in diffuse TBI (dTBI), there was select reduction of specific dendrite-targeting neurons in sensory cortex and hippocampus while in motor cortex there was up-regulation of specific dendrite-targeting neurons. ⋯ However, DG of hippocampus now showed reduction of dendrite-targeting inhibitory neurons. Finally, with respect to motor cortex, there was an upregulation of dendrite-targeting interneurons in the supragranular layers at 24 h returning to normal levels by 2 weeks. Overall, our findings reconfirm that dendritic inhibition is particularly susceptible to brain trauma, but also show that there are complex brain-area-specific changes in inhibitory neuronal numbers and in compensatory changes, rather than a simple monotonic progression of changes post-dTBI.
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The aim of this cross-sectional study was to determine the associations of objectively assessed habitual physical activity and physical performance with brain plasticity outcomes and brain-derived neurotrophic factor (BDNF) levels in cognitively healthy older adults. Physical performance was analyzed based on cardiopulmonary exercise-testing data and accelerometer-based physical activity was analyzed as total activity counts, sedentary time, light physical activity and moderate to vigorous physical activity. Brain plasticity outcomes included magnetic resonance spectroscopy (MRS)-based markers, quantitative imaging-based hippocampal volume and BDNF serum levels. ⋯ In this study these associations were not mediated significantly by physical performance. Overall physical activity and exceeding current moderate to vigorous physical activity recommendations were positively associated with BDNF. Sedentary behavior, however, seems to be negatively related to neurotrophic factor bioavailability in the elderly.
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Objects play vital roles in scene categorization. Although a number of studies have researched on the neural responses during object and object-based scene recognition, few studies have investigated the neural mechanism underlying object-masked scene categorization. Here, we used functional magnetic resonance imaging (fMRI) to measure the changes in brain activations and functional connectivity (FC) while subjects performed a visual scene-categorization task with different numbers of 'signature objects' masked. ⋯ Another core hub was found in left middle temporal gyrus (MTG) and its connection with middle cingulate cortex (MCC), supramarginal gyrus (SMG) and insula might serve in the processing of motor response and the semantic relations between objects and scenes. Brain-behavior correlation analysis substantiated the contributions of the FC to the different processes in the object-masked scene-categorization tasks. Altogether, the results suggest that masking of objects significantly affected the object attention, cognitive demand, top-down modulation effect, and semantic judgment.