Abstract
Previous studies have shown that spinal neural circuits are modulated by motor skill training. However, the effects of task movement speed on changes in spinal neural circuits have not been clarified. The aim of this research was to investigate whether spinal neural circuits were affected by task movement speed. Thirty-eight healthy subjects participated in this study. In experiment 1, the effects of task movement speed on the spinal neural circuits were examined. Eighteen subjects performed a visuomotor task involving ankle muscle slow (nine subjects) or fast (nine subjects) movement speed. Another nine subjects performed a non-visuomotor task (controls) in fast movement speed. The motor task training lasted for 20 min. The amounts of D1 inhibition and reciprocal Ia inhibition were measured using H-relfex condition-test paradigm and recorded before, and at 5, 15, and 30 min after the training session. In experiment 2, using transcranial magnetic stimulation (TMS), the effects of corticospinal descending inputs on the presynaptic inhibitory pathway were examined before and after performing either a visuomotor (eight subjects) or a control task (eight subjects). All measurements were taken under resting conditions. The amount of D1 inhibition increased after the visuomotor task irrespective of movement speed (P < 0.01). The amount of reciprocal Ia inhibition increased with fast movement speed conditioning (P < 0.01), but was unchanged by slow movement speed conditioning. These changes lasted up to 15 min in D1 inhibition and 5 min in reciprocal Ia inhibition after the training session. The control task did not induce changes in D1 inhibition and reciprocal Ia inhibition. The TMS conditioned inhibitory effects of presynaptic inhibitory pathways decreased following visuomotor tasks (P < 0.01). The size of test H-reflex was almost the same size throughout experiments. The results suggest that supraspinal descending inputs for controlling joint movement are responsible for changes in the spinal neural circuits, and that task movement speed is one of the critical factors for inducing plastic changes in reciprocal Ia inhibition.
Highlights
Plastic changes in cortical areas induced by motor skill training have been investigated, and results suggest they are related to the acquisition of motor skills (Karni et al, 1995; Pascual-Leone et al, 1995; Muellbacher et al, 2001, 2002; Perez et al, 2004)
Baseline characteristics of subjects among groups were wellmatched in the Experiment 1 and the Experiment 2 groups (Table 1), and there were no significant differences between all baseline measures
The main findings of our study suggest that: (i) the amount of presynaptic inhibition is increased after visuomotor tasks irrespective of task movement speed; (ii) changes in the reciprocal Ia inhibition are affected by task movement speed, and are increased in fast movement speed conditions, but unchanged in slow movement speed conditions; (iii) nonvisuomotor tasks do not induce any changes in presynaptic inhibition and reciprocal Ia inhibition; and (iv) transcranial magnetic stimulation (TMS) conditioned inhibitory effects on the presynaptic inhibitory pathway are changed following visuomotor tasks
Summary
Plastic changes in cortical areas induced by motor skill training have been investigated, and results suggest they are related to the acquisition of motor skills (Karni et al, 1995; Pascual-Leone et al, 1995; Muellbacher et al, 2001, 2002; Perez et al, 2004). It was reported that active-dependent plasticity develops at cortical levels and at the spinal level (Wolpaw, 2007). In support of this concept, previous studies showed that motor skill training could induce reorganization of the spinal cord, which might account for the improvement of motor performance (Perez et al, 2005; Mazzocchio et al, 2006; Meunier et al, 2007; Roche et al, 2011). Previous studies have shown that presynaptic inhibition is one of the key mechanisms in the spinal cord to regulate these sensory signals (Seki et al, 2003; Seki and Fetz, 2012). Changes in the sensory inputs at preneuron levels contribute to the control of the spinal reflexes, such as the stretch reflex and/or cutaneous reflex (Sinkjaer and Hayashi, 1989; Bawa and Sinkjaer, 1999)
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