Threshold position control of anticipation in humans: a possible role of corticospinal influences
Threshold position control of anticipation in humans: a possible role of corticospinal influences
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人类预期的阈值位置控制：皮质脊髓影响的可能作用
DOI：
10.1113/jp274309
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
A. Feldman
中科院分区：
文献类型：
--
作者：
L. Zhang;N. Turpin;A. Feldman
要点突然卸载预加载的手腕肌肉会引起手腕运动到新的位置。如果受试者使用对侧手臂卸载肌肉（自卸载），则可以防止这种运动。源自初级运动皮层的皮质脊髓影响在突然卸载之前维持对手腕肌肉运动神经元的强直影响，但在自卸载开始之前和结束之前修改这些影响。结果是基于先前的发现解释的，即有意的动作是由手腕运动神经元的空间阈值的中枢，特别是皮质脊髓的变化引起的。激活，从而预先确定神经肌肉外围与环境力实现机械平衡的吸引点。通过维持或改变阈值，下降系统让身体节段在各自的卸载任务中达到平衡位置，而无需预先编程运动学或肌肉激活模式。这项研究增进了对一般运动动作，特别是预期如何控制的理解。摘要：皮质脊髓（CS）通路在预期运动动作中的作用通过使用评估初级运动皮层的经颅磁刺激（TMS）投射到腕部肌肉的运动神经元（MN）。实验者或受试者用另一只手突然卸载预加载的腕屈肌（自卸载）。突然卸载后，腕关节不由自主地弯曲到新的位置。相反，在自卸过程中，手腕几乎保持不动，这意味着发生了预期的姿势调整。在自卸载任务中，预期表现为在背景肌电图活动变化前约 72 毫秒开始预激活的屈肌 MN 的下降促进减少。约 61 毫秒后，伸肌 MN 的下降促进开始增加。相反，这些影响在突然卸载之前保持不变，意味着缺乏预期。我们还测试了短暂肌肉缩短产生的肌电图静默期的 TMS 反应，在自卸载开始前和结束后短暂地产生相似的肌电图水平。我们发现自卸载后屈肌 MN 的下降促进减少。为了解释为什么由于下降影响的这些变化，手腕偏移在自卸载中被最小化，我们依赖于之前的演示，即下降系统预设了肌肉开始激活的身体部位的阈值位置，从而预先确定了系统被吸引的平衡点。基于这个概念，与运动学和/或肌电图模式的直接预编程的替代概念相比，提出了对两种类型卸载中的运动学、肌电图和下降模式的更一致的解释。
Key pointsSudden unloading of preloaded wrist muscles elicits motion to a new wrist position. Such motion is prevented if subjects unload muscles using the contralateral arm (self‐unloading).Corticospinal influences originated from the primary motor cortex maintain tonic influences on motoneurons of wrist muscles before sudden unloading but modify these influences prior to the onset and until the end of self‐unloading.Results are interpreted based on the previous finding that intentional actions are caused by central, particularly corticospinal, shifts in the spatial thresholds at which wrist motoneurons are activated, thus predetermining the attractor point at which the neuromuscular periphery achieves mechanical balance with environment forces.By maintaining or shifting the thresholds, descending systems let body segments go to the equilibrium position in the respective unloading tasks without the pre‐programming of kinematics or muscle activation patterns.The study advances the understanding of how motor actions in general, and anticipation in particular, are controlled.AbstractThe role of corticospinal (CS) pathways in anticipatory motor actions was evaluated using transcranial magnetic stimulation (TMS) of the primary motor cortex projecting to motoneurons (MNs) of wrist muscles. Preloaded wrist flexors were suddenly unloaded by the experimenter or by the subject using the other hand (self‐unloading). After sudden unloading, the wrist joint involuntarily flexed to a new position. In contrast, during self‐unloading the wrist remained almost motionless, implying that an anticipatory postural adjustment occurred. In the self‐unloading task, anticipation was manifested by a decrease in descending facilitation of pre‐activated flexor MNs starting ∼72 ms before changes in the background EMG activity. Descending facilitation of extensor MNs began to increase ∼61 ms later. Conversely, these influences remained unchanged before sudden unloading, implying the absence of anticipation. We also tested TMS responses during EMG silent periods produced by brief muscle shortening, transiently resulting in similar EMG levels before the onset and after the end of self‐unloading. We found reduced descending facilitation of flexor MNs after self‐unloading. To explain why the wrist excursion was minimized in self‐unloading due to these changes in descending influences, we relied on previous demonstrations that descending systems pre‐set the threshold positions of body segments at which muscles begin to be activated, thus predetermining the equilibrium point to which the system is attracted. Based on this notion, a more consistent explanation of the kinematic, EMG and descending patterns in the two types of unloading is proposed compared to the alternative notion of direct pre‐programming of kinematic and/or EMG patterns.
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