Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Motor skill training induces changes in the excitability of the leg cortical area in healthy humans.
Training-induced changes in cortical excitability may play an important role in rehabilitation of gait ability in patients with neurological disorders. In this study, we investigated the effect of a 32-min period of motor skill, non-skill and passive training involving the ankle muscles on leg motor cortical excitability in healthy humans. Transcranial magnetic stimulation (TMS) at a range of intensities was applied to obtain a recruitment curve of the motor evoked potentials (MEPs) in the tibialis anterior (TA) muscle before and after training. ⋯ SICI was decreased after 32 min of motor skill training but no changes were observed in ICF. We conclude that similar plastic changes as have previously been reported for the hand motor following motor skill training may also be observed for the leg motor area. The observed plastic changes appeared to be related to the degree of difficulty in the motor task, and may be of relevance for rehabilitation of gait disorders.
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Comparative Study
Neuromuscular and biomechanical coupling in human cycling: modulation of cutaneous reflex responses to sural nerve stimulation.
This study tested the hypothesis that the modulation of cutaneous reflexes during human cycling would be dependent on muscle biomechanical function and phase of leg movement. The coupling between neuromuscular (electromyographic, EMG), kinetic and kinematic responses to brief innocuous (75% of the pain threshold PnT) and noxious (125% PnT) sural nerve stimulation were studied. Stimuli were delivered pseudorandomly at eight equidistant (45 degrees) positions of the crank cycle. ⋯ We conclude that sural nerve stimulation during human cycling evokes distinct reflex responses in muscles operating around the knee (BF and RF) and the ankle (TA and SOL). These reflexes are modulated in a phase-dependent manner depending on muscle biomechanical function to generate energy for limb and crank propulsion during a specific region in the cycle. This modulation contributed to a specific adaptation of joint motion and force production in order to maintain task performance.
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Comparative Study
Fooling the brain into thinking it sees both hands moving enhances bimanual spatial coupling.
This study examined the hypothesis that the mirror reflection of one hand's movement directly influences motor output of the other (hidden) hand, during performance of bimanual drawing. A mirror was placed between the two hands during bimanual circle drawing, with one hand and its reflection visible and the other hand hidden. Bimanual spatial coupling was enhanced by the mirror reflection, as shown by measures of circle size. ⋯ There was no evidence of a consistent phase lead of the visible hand, which indicates that the observed effects on spatial coupling were immediate and not based on time-consuming feedback processes. We argue that visual mirror symmetry fools the brain into believing it sees both hands moving rather than one. Consequently, the spatial properties of movement of the two hands become more similar through a process that is virtually automatic.
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Hitherto, it has proven difficult to investigate interactions between cerebral and brainstem motor systems in the human. We hypothesised that transcranial magnetic stimulation (TMS) centred over the dorsal premotor and primary motor cortices might elicit net facilitatory cortico-reticular effects that could interact at the level of the brainstem with a habituated startle to give a reticulospinal discharge and electromyographic (EMG) response with a longer latency than the direct corticospinal response. Conversely, any reticulo-cortical activity evoked by a habituated startle should influence the size of the direct response to cortical TMS. ⋯ Indeed, an actual increase in EMG over baseline levels occurred in the later half of the silent period in all subjects. We conclude that both cortico-reticular and reticular-cortical effects could be elicited in deltoid through the combination of acoustic stimulation and TMS at short interstimulus intervals. Effects were similar with TMS over premotor and primary motor cortex.
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Weak transcranial direct current stimulation (tDCS) can induce long lasting changes in cortical excitability. In the present study we asked whether tDCS applied to the left primary motor cortex (M1) also produces aftereffects distant from the site of the stimulating electrodes. We therefore tested corticospinal excitability in the left and the right M1 and transcallosal excitability between the two cortices using transcranial magnetic stimulation (TMS) before and after applying tDCS. ⋯ MEPs evoked from the right M1 were unchanged whilst the duration of transcallosal inhibition evoked from the right M1 was shortened after cathodal tDCS and prolonged after anodal tDCS. The duration of transcallosal inhibition returned to control values before the effect on the MEPs from the left M1 had recovered. These findings are compatible with the idea that tDCS-induced aftereffects in the cortical motor system are limited to the stimulated hemisphere, and that tDCS not only affects corticospinal circuits involved in producing MEPs but also inhibitory interneurons mediating transcallosal inhibition from the contralateral hemisphere.