The European journal of neuroscience
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Experimental studies emphasize the importance of homeostatic plasticity as a mean of stabilizing the properties of neural circuits. In the present work we combined two techniques able to produce short-term (5-Hz repetitive transcranial magnetic stimulation, rTMS) and long-term (transcranial direct current stimulation, tDCS) effects on corticospinal excitability to evaluate whether and how the effects of 5-Hz rTMS can be tuned by tDCS preconditioning. Twelve healthy subjects participated in the study. ⋯ After facilitatory preconditioning with anodal tDCS, 5-Hz rTMS failed to produce progressive MEP facilitation. Conversely, when 5-Hz rTMS was preceded by inhibitory cathodal tDCS, MEP facilitation was not abolished. These findings may give insight into the mechanisms of homeostatic plasticity in the human cerebral cortex, suggesting also more suitable applications of tDCS in a clinical setting.
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We compared the effect of viral administration of brain-derived neurotrophic factor (BDNF) or neurotrophin 3 (NT-3) on locomotor recovery in adult rats with complete thoracic (T10) spinal cord transection injuries, in order to determine the effect of chronic neurotrophin expression on spinal plasticity. At the time of injury, BDNF, NT-3 or green fluorescent protein (GFP) (control) was delivered to the lesion via adeno-associated virus (AAV) constructs. AAV-BDNF was significantly more effective than AAV-NT-3 in eliciting locomotion. ⋯ Elevated nuclear c-Fos expression in interneurons located in the L2 intermediate zone after AAV-BDNF treatment indicated increased activation of interneurons in the vicinity of the locomotor central pattern generator. AAV-NT-3 treatment reduced motoneuron excitability, with little change in c-Fos expression. These results support the potential for BDNF delivery at the lesion site to reorganize locomotor circuits.
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Pain communication is thought to promote automatic vicarious self-protective responses as well as empathic concern towards others' suffering. This duality was recently highlighted in a study showing that highly empathic individuals display increased vicarious facilitation of low-level pain processing (nociceptive flexion reflex, NFR) combined with an unexpected reduced facilitation of self-pain perception (pain ratings) while viewing static pictures evoking pain in others. The present study sought to test further the moderating effects of dispositional empathy on vicarious responses induced by viewing dynamic pain expressions. ⋯ Viewing stronger pain expressions generally increased shock-pain unpleasantness ratings, the amplitude of the NFR, and facial responses (corrugator muscle) to the noxious stimulation. However, self-pain ratings (intensity and unpleasantness) increased less or were reduced following clips of pain expression in individuals scoring higher on the Empathy Quotient. These results suggest that vicarious processes facilitate low-level defensive responses, while the experience of self-pain and the associated negative affect may be partly tuned-down by higher-order empathic processes.
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There is some limited evidence suggesting that the spaced application of repetitive transcranial magnetic stimulation (rTMS) protocols may extend the duration of induced neuroplastic changes. However, this has yet to be demonstrated in the human primary motor cortex (M1). We evaluated whether the paired application of an inhibitory rTMS protocol [continuous theta burst stimulation (cTBS)] at 10-min intervals prolonged the duration of induced M1 plasticity. ⋯ Control experiments suggested that the contraction used to establish active motor threshold prior to cTBS application may be responsible for blocking the effect of paired cTBS trains at AMT(80). The results suggest that the spaced application of cTBS protocols may be an effective approach for establishing long-lasting M1 neuroplasticity only in the absence of prior voluntary motor activation. These findings may have important implications for the therapeutic application of rTMS.