Lundbye-Jensen Jesper, Nielsen Jens Bo
Department of Neuroscience and Pharmacology, University of Copenhagen, Panum Institute 22.3, Blegdamsvej 3, Copenhagen 2200, Denmark.
J Appl Physiol (1985). 2008 Jul;105(1):139-51. doi: 10.1152/japplphysiol.00687.2007. Epub 2008 May 1.
Plastic neural changes have been documented in relation to different types of physical activity, but little is known about central nervous system plasticity accompanying reduced physical activity and immobilization. In the present study we investigated whether plastic neural changes occur in relation to 1 wk of immobilization of the nondominant wrist and hand and a corresponding period of recovery in 10 able-bodied volunteers. After immobilization, maximal voluntary contraction torque decreased and the variability of submaximal static contractions increased significantly without evidence of changes in muscle contractile properties. Hoffmann (H)-reflex amplitudes and the ratios of H-slope to M-slope increased significantly in flexor carpi radialis and abductor pollicis brevis at rest and during contraction without changes in corticospinal excitability, estimated from motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation. Corticomuscular coherence measures were derived from EEG and EMG obtained during static contractions. After immobilization, corticomuscular coherence in the 15- to 35-Hz range associated with maximum negative cumulant values at lags corresponding to MEP latencies decreased. One week after cast removal, all measurements returned to preimmobilization levels. The increased H-reflex amplitudes without changes in MEPs may suggest that presynaptic inhibition or postactivation depression of Ia afferents is reduced following immobilization. Reduced corticomuscular coherence may be caused by changes in afferent input at spinal and cortical levels or by changes in the descending drive from motor cortex. Further studies are needed to elucidate the mechanisms underlying the observed increased spinal excitability and reduced coupling between motor cortex and spinal motoneuronal activity following immobilization.
与不同类型的体育活动相关的可塑性神经变化已有文献记载，但对于伴随体育活动减少和固定不动而出现的中枢神经系统可塑性却知之甚少。在本研究中，我们调查了10名身体健全的志愿者非优势手腕和手部固定1周及相应恢复期后是否会发生可塑性神经变化。固定后，最大自主收缩扭矩降低，次最大静态收缩的变异性显著增加，而肌肉收缩特性无变化迹象。在静息和收缩时，桡侧腕屈肌和拇短展肌的霍夫曼（H）反射幅度以及H波斜率与M波斜率之比显著增加，经颅磁刺激诱发的运动诱发电位（MEP）估计皮质脊髓兴奋性无变化。皮质肌肉相干性测量是从静态收缩期间获得的脑电图和肌电图得出的。固定后，与对应于MEP潜伏期的滞后处最大负累积值相关的15至35赫兹范围内的皮质肌肉相干性降低。去除石膏1周后，所有测量值均恢复到固定前水平。H反射幅度增加而MEP无变化可能表明固定后Ia传入神经的突触前抑制或激活后抑制降低。皮质肌肉相干性降低可能是由脊髓和皮质水平的传入输入变化或运动皮层下行驱动变化引起的。需要进一步研究以阐明固定后观察到的脊髓兴奋性增加以及运动皮层与脊髓运动神经元活动之间耦合减少的潜在机制。
