Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Whether a cortical drive to one limb modulates interhemispheric inhibition (IHI) from the active targeting to the non-active motor cortex (M1) remained unclear. The present study using a conditioning-test transcranial magnetic stimulation (TMS) paradigm aimed to directly demonstrate the modulation of IHI during unilateral voluntary or imagined movement in humans. Subjects were asked to actually perform right index-finger abduction (10-70% of the maximum voluntary contraction) or to imagine the movement. ⋯ Importantly, the MEP inhibition was markedly enhanced during voluntary or imagined movement in comparison with that at rest. The regression analysis revealed that IHI varied depending on the intensity of the impulses conveyed from left to right M1, but not on the corticospinal excitability of the active right hand. Our results suggest that IHI from the active to non-active M1 is enhanced during unilateral volitional motor activity.
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We investigated the processing of self-related information under the prime paradigm using event-related potentials (ERPs) to provide evidence for implicit self-positivity bias in Chinese individuals. Reaction times and ERPs were recorded when participants made positive/negative emotional judgments to personality-trait adjectives about themselves or others. ⋯ Larger N400 amplitudes elicited by words that were inconsistent with the self-positivity bias, suggesting that accessing non-self-relevant information is more difficult than self-relevant information. Thus, P300 and N400 could be used as neuro-indexes of the implicit self-positivity bias.
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Randomized Controlled Trial
Novelty detection is enhanced when attention is otherwise engaged: an event-related potential study.
Novel stimuli are detected and evaluated quickly, suggesting that processing them is a priority for the brain. In the present study, the effects of attention on this early visual novelty processing were investigated in two experiments using the event-related potential (ERP) technique. In the first experiment, participants performed two tasks that varied in the amount of attention available for novel stimuli. ⋯ In a second experiment, a condition was added in which working memory load was low, but visual oddball stimuli were task-irrelevant. Results from this experiment showed that while the reduction in P3a amplitude was due to task irrelevance, the enhanced anterior N2 was linked to a high working memory load. This suggests that novelty detection is enhanced when attention is otherwise engaged.
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In healthy participants, high-frequency electrical stimulation of the forearm not only evokes local hyperalgesia but also inhibits sensitivity to pressure-pain in the ipsilateral forehead, possibly due to activation of ipsilateral inhibitory pain modulation processes. The aim of this study was to compare the effects of high- and low-frequency electrical stimulation of the forearm on sensitivity to pressure-pain in the ipsilateral forehead, as inhibitory pain modulation may be stronger after low- than high-frequency electrical stimulation. Before and after high- and low-frequency electrical stimulation, sensitivity to heat and to blunt and sharp stimuli was assessed at and adjacent to the electrically conditioned site in the forearm. ⋯ This decrease was associated with heightened sensitivity to pressure-pain at the electrically conditioned forearm site and with diminished sensitivity to heat around this site. These findings suggest that sensitisation of pressure-sensitive nociceptive afferents at the site of electrical stimulation is associated with generation of an ipsilateral pain-inhibitory process. This ipsilateral pain-inhibitory process may decrease sensitivity to pressure-pain in the ipsilateral forehead and suppress secondary hyperalgesia to heat.
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Central pain is one of the most important complications after spinal cord injury (SCI), and thereby, its treatment raises many challenges. After SCI, in a cascade of molecular events, a marked increase in glutamate at the injury site results in secondary changes which may impact on supraspinal regions, mainly ventroposterolateral (VPL). There is little information about the changes in glutamate metabolism in the VPL and whether it contributes to SCI-related central pain. ⋯ Glutamate levels were significantly increased in ipsilateral VPL of spinal-cord-injured rats 2 weeks after SCI and remained high up to day 28 post-surgery. The STT lesions had no marked effect on our measures of motor activity, but there was a significant decrease in paw withdrawal threshold in the hind paws at day 14 post-SCI. These findings suggest that an increased release of glutamate in VPL plays a role in secondary pathologic changes, leading to neuronal hyperexcitation and neuropathic pain after SCI.