Department of Integrative Physiology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Japan.
BMC Neurosci. 2013 Mar 13;14:28. doi: 10.1186/1471-2202-14-28.
Widespread interlimb reflexes evoked in leg muscles by cutaneous stimulation of the hand are phase-modulated and behaviorally relevant to produce functional changes in ankle trajectory during walking. These reflexes are complementary to the segmental responses evoked by stimulation at the ankle. Despite differences in the expression of reflex amplitude based upon site of nerve stimulation, there are some common features as well, suggesting the possibility of shared interneuronal pathways. Currently little is known about integration or shared reflex systems from interlimb cutaneous networks during human locomotion. Here we investigated convergent reflex effects following cutaneous stimulation of the hand and foot during arm and leg cycling (AL) by using spatial facilitation. Participants performed AL cycling and static activation of the target muscle knee extensor vastus lateralis (VL) in 3 different randomly ordered nerve stimulation conditions: 1) superficial radial nerve (SR; input from hand); 2) superficial peroneal nerve (SP; input from foot); and, 3) combined stimulation (SR + SP). Stimuli were applied around the onset of rhythmic EMG bursts in VL corresponding to the onset of the power or leg extension phase.
During AL cycling, small inhibitory (80 ms) and large facilitatory reflexes (100 ~ 150 ms) were seen in VL. The amplitudes of the facilitatory responses with SR + SP stimulation were significantly larger than those for SP or SR stimulation alone. The facilitation was also significantly larger than the simple mathematical summation of amplitudes from SP and SR trials. This indicates extra facilitation beyond what would be accounted for by serial neuronal processing and was not observed during static activation.
We conclude that AL cycling activates shared interneurons in convergent reflex pathways from cutaneous inputs innervating the hand and leg. This enhanced activity has functional implications for corrective responses during locomotion and for translation to rehabilitation after neurotrauma.
手部皮肤刺激诱发的腿部肌肉广泛的肢体间反射是相位调制的，与行走时踝关节轨迹的功能变化有关。这些反射与刺激踝关节引起的节段性反应互补。尽管基于神经刺激部位的反射幅度表达存在差异，但也存在一些共同特征，这表明存在共享的中间神经元通路的可能性。目前，对于人类运动过程中来自肢体间皮肤网络的整合或共享反射系统知之甚少。在这里，我们通过空间促进研究了手臂和腿部循环（AL）期间手部和足部皮肤刺激后的会聚反射效应。参与者在 3 种不同的随机顺序神经刺激条件下进行 AL 循环和目标肌肉股外侧肌（VL）的静态激活：1）桡神经浅支（SR；手部输入）；2）腓浅神经（SP；足部输入）；3）联合刺激（SR + SP）。刺激在 VL 中的节律性 EMG 爆发开始时施加，对应于功率或腿部伸展阶段的开始。
在 AL 循环期间，VL 中出现小的抑制性（80 ms）和大的易化性反射（100~150 ms）。SR + SP 刺激的易化反应幅度明显大于 SP 或 SR 单独刺激的幅度。易化也明显大于 SP 和 SR 试验的简单数学总和。这表明额外的易化超出了串行神经元处理所能解释的范围，并且在静态激活期间没有观察到。
我们得出结论，AL 循环激活了来自手部和腿部皮肤传入的会聚反射途径中的共享中间神经元。这种增强的活动对运动过程中的矫正反应以及神经创伤后的康复翻译具有功能意义。
