Connecting the micro with the macro level in motor control: unravelling general sensory influences on leg stepping
Connecting the micro with the macro level in motor control: unravelling general sensory influences on leg stepping
复制标题
将运动控制中的微观与宏观联系起来：揭示对腿部迈步的一般感官影响
DOI：
10.1113/jp278031
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
A. Büschges
中科院分区：
文献类型：
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作者：
A. Büschges
动物是如何产生其物种特异性运动活动的？今天，动物王国中众所周知，运动输出的周期性，无论是爬行，游泳，行走还是飞行，都是基于中枢神经系统中神经网络的节律活动，所谓的中枢模式发生器（CPG;关于各种动物准备和方法的评论，请参见Hooper & Büschges，2017）。来自神经系统高级中枢的下行信号启动、维持、调节和停止这些运动CPG的活动，这些CPG位于中枢神经系统下游，紧邻运动器官（例如，Grätsch等人，2019）。通过来自运动器官（例如，附肢）的局部感觉反馈信号以及协调控制各个运动器官的网络之间（例如，控制用于行走的单腿的网络之间）的神经信号，CPG的活动被进一步修改为功能性运动输出。在行走中，已知感觉反馈有助于在迈步的站立和摆动阶段以及两个阶段之间的过渡期间产生和控制肌肉活动（例如Pearson，2004; Büschges等人，2011）。例如，站立的产生通过来自感觉器官的感觉信号来辅助和加强，所述感觉器官监测肢体段的运动和负荷。在哺乳动物中，这些信号由Ia组和II组传入神经（来自所谓的肌梭）和Ib组传入神经（来自所谓的高尔基体腱器官）提供。这些见解通常是从简化的准备工作中获得的，这些准备工作详细关注了对来自臀部、股骨或胫骨肌肉的特定感觉器官进行机械刺激后，腿部肌肉亚组中产生的运动活动，例如在猫中（例如Pearson，2004年的综述）。尽管这些见解的神经元机制有助于控制地面运动，我们的知识的神经反馈信号的一般贡献，从特定类型的感觉器官，如肌梭产生的步进运动，仍然是不完整的。为了填补这一空白，有三种方法的实验是必要的：（i）在体内运动过程中记录大量运动元件的协同动作，（ii）在运动过程中记录腿部运动的运动学参数，以及（iii）在其他完整的动物中选择性地去除一种特定类型的感觉反馈。通过将上述三种方法与计算技术相结合，在本期《生理学杂志》的一篇文章中，Santuz及其同事（2019）讨论了步行过程中肌梭反馈的作用，即来自监测腿部肌肉运动的感觉器官（另见Akay et al. 2014）。作者揭示了与哺乳动物腿部运动相关的感觉反馈在多大程度上有助于协调激活多块肌肉，这些肌肉是功能性步进运动的基础。为此，作者分析和比较了野生型小鼠和骨骼肌中缺乏肌梭传入的突变小鼠Egr 3 −/−小鼠之间的运动活动（Tourtelevision & Milbrandt，1998）。作者通过高速视频记录和同步肌电图记录多达七个腿部肌肉（移动髋关节、膝关节和踝关节）来监测运动活动。他们通过挑战运动输出对扰动的鲁棒性来详细说明肌梭反馈的作用。为此，他们通过隐神经的电刺激来扰乱行走，引起蹒跚的纠正反应（Mayer和Akay，2018），导致动物在刺激之间更加谨慎地行走。最后，作者通过监测游泳过程中的肌肉活动来测试Egr 3 −/−小鼠中高尔基体肌腱器官的力反馈的潜在补偿作用，在这种情况下，由于浮力引起的重力负荷较低，来自这些传入的反馈减少。他们的研究结果为腿部的肌梭反馈提供了证据，有助于在步进过程中以及在更大程度上在游泳过程中腿部运动输出的准确时间协调。重要的是，他们发现肌梭反馈是腿部肌肉控制系统科普外部扰动的先决条件。在缺乏肌梭反馈的小鼠中，与完整条件的偏差对于游泳比步进电机输出更强。这表明，来自高尔基腱器官的力反馈可以补偿在这些条件下缺乏运动反馈，当它们的反馈增益足够高时，由于浮力引起的较低重力负荷，游泳中不存在这种情况。总之，这项研究提出了一个结论性的答案，从腿部肌肉的肌梭反馈的作用，在产生一个功能性运动输出的哺乳动物腿部肌肉控制系统步进的问题。值得注意的是，作者通过描述和分析多块肌肉的运动学和运动输出，利用基于运动活动的神经控制受益于肌肉协同作用的理论框架来实现他们的见解（例如Bizzi et al. 2008; Cappelini et al. 2006）。他们使用评估和分类方案来识别和比较肌肉协同作用的时间依赖性和时间无关性成分（即“运动基元”和“运动模块”）。这一点使得这项研究对于运动控制领域的神经科学家来说非常有趣，特别是那些研究其他动物进行陆地运动的神经科学家。
How do animals generate their speciesspecific locomotor activity? Today it is well known across the animal kingdom that the cyclic nature of a locomotor output, be it for crawling, swimming, walking or flying, is based on rhythmic activity of neural networks in the central nervous system, so-called central pattern generators (CPGs; for review on various animal preparations and approaches see Hooper & Büschges, 2017). Descending signals from higher order centres in the nervous system initiate, maintain, regulate and stop the activity of these locomotor CPGs, which are situated downstream in the central nervous system in close vicinity to the locomotor organs (e.g. Grätsch et al. 2019). The activity of CPGs is further modified towards a functional locomotor output by local sensory feedback signals from the locomotor organs, e.g. appendages, and coordinating neural signals between the networks controlling individual locomotor organs, e.g. between networks controlling single legs for walking. In walking, sensory feedback is known to contribute to generation and control of muscle activity during the stance and swing phases of stepping as well as to the transitions between the two phases (e.g. Pearson, 2004; Büschges et al. 2011). For example, the generation of stance is assisted and reinforced by sensory signals from sense organs monitoring movement and load of limb segments. Those signals are provided in mammals by group Ia and group II afferents, arising from the so-called muscle spindles, and group Ib afferents, arising from the so-called Golgi tendon organs. These insights were often gained from reduced preparations focusing in detail on the motor activity generated in subsets of the leg muscles upon mechanical stimulation of specific sensory organs from the muscles of hip, femur, or the tibia, for example in the cat (e.g. review in Pearson, 2004). Despite these insights on neuronal mechanisms contributing to the control of terrestrial locomotion, our knowledge on the general contribution of the neural feedback signals from specific types of sense organs, e.g. the muscle spindles to the generation of stepping movements, is still incomplete. To fill this gap, experiments with three approaches are necessary: (i) the recording of the concerted action of a large number of motor elements during in vivo locomotion, (ii) the recording of the kinematic parameters of the leg movement during locomotion, and (iii) the selective removal of sensory feedback of one specific kind in an otherwise intact animal. By combining the three approaches described above with computational techniques, in an article in this issue of The Journal of Physiology, Santuz and colleagues (2019) addressed the role of feedback from the muscle spindles during walking, i.e. from sense organs monitoring movements of the leg muscles (see also Akay et al. 2014). The authors unravel to what extent sensory feedback related to movement from a mammalian leg contributes to the coordinated activation of multiple muscles that underlie functional stepping movements. To do so, the authors analyse and compare the locomotor activity between wild-type mice and mutant mice lacking muscle spindle afferents in their skeletal muscles, the Egr3−/− mice (Tourtellotte & Milbrandt, 1998). The authors monitor locomotor activity by means of high-speed viodeographic recording and simultaneous electromyographic recording of up to seven leg muscles that move the hip, knee and ankle joints. They specify the detailed role of muscle spindle feedback by challenging the robustness of the motor output generated against perturbations. To do so, they perturb walking by electrical stimulations of the saphenous nerve that elicit stumbling corrective reactions (Mayer and Akay, 2018) causing the animal to exert a more cautious walking in between the stimulations. Finally, the authors test for the potential compensatory role of force feedback from Golgi tendon organs in the Egr3−/− mice by monitoring muscle activity during swimming, a situation, in which feedback from these afferents is reduced due to the lower gravitational load induced by buoyancy. The results of their study provide evidence for muscle spindle feedback from a leg to be instrumental for accurate temporal coordination of the leg motor output during stepping and to an even larger extent during swimming. Importantly, they found muscle spindle feedback to represent the prerequisite for the leg muscle control system to cope with external perturbations. In mice lacking muscle spindle feedback, deviations from intact conditions were much stronger for the swimming than the stepping motor output. This suggests that force feedback from Golgi tendon organs can compensate for the lack of movement feedback under these conditions, when their feedback gain is high enough, a situation which is not present in swimming due to the lower gravitational load induced by buoyancy. In summary, this study presents a conclusive answer to the question of the role muscle spindle feedback from leg muscles plays in the generation of a functional locomotor output of a mammalian leg muscle control system for stepping. It is important to note that the authors achieve their insights by describing and analysing the movement kinematics and motor output in multiple muscles utilizing a theoretical framework based on the notion that the neural control of motor activity is profiting from muscle synergies (e.g. Bizzi et al. 2008; Cappelini et al. 2006). They use evaluation and classification schemes to identify and compare the time-dependent and time-independent components of muscle synergies (i.e. the ‘motor primitives’ and ‘motor modules’). This aspect renders this study very interesting for neuroscientists in the field of motor control in general, and in particular, for those neuroscientists that work on other animals performing terrestrial locomotion.
在存在或不存在肌梭感觉反馈的情况下小鼠运动模式的模块化组织
DOI：
10.1113/jp277515
发表时间：
2019
期刊：
The Journal of Physiology
影响因子：
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作者：
Santuz A;Akay T;Mayer WP;Wells TL;Schroll A;Arampatzis A
通讯作者：
Arampatzis A