Vibert N, MacDougall H G, de Waele C, Gilchrist D P, Burgess A M, Sidis A, Migliaccio A, Curthoys I S, Vidal P P
Laboratoire de Neurobiologie des Reseaux Sensorimoteurs, CNRS, ESA 7060, 45 rue des Saints-Peres, 75270 Paris cedex 06, France.
J Physiol. 2001 May 1;532(Pt 3):851-68. doi: 10.1111/j.1469-7793.2001.0851e.x.
The aim of this study was to determine how context and on-line sensory information are combined to control posture in seated subjects submitted to high-jerk, passive linear accelerations. Subjects were seated with eyes closed on a servo-controlled linear sled. They were asked to relax and received brief accelerations either sideways or in the fore-aft direction. The stimuli had an abrupt onset, comparable to the jerk experienced during a minor car collision. Rotation and translation of the head and body were measured using an Optotrak system. In some of the subjects, surface electromyographic (EMG) responses of selected neck and/or back muscles were recorded simultaneously. For each subject, responses were highly stereotyped from the first trial, and showed little sign of habituation or sensitisation. Comparable results were obtained with sideways and fore-aft accelerations. During each impulse, the head lagged behind the trunk for several tens of milliseconds. The subjects' head movement responses were distributed as a continuum in between two extreme categories. The 'stiff' subjects showed little rotation or translation of the head relative to the trunk for the whole duration of the impulse. In contrast, the 'floppy' subjects showed a large roll or pitch of the head relative to the trunk in the direction opposite to the sled movement. This response appeared as an exaggerated 'inertial' response to the impulse. Surface EMG recordings showed that most of the stiff subjects were not contracting their superficial neck or back muscles. We think they relied on bilateral contractions of their deep, axial musculature to keep the head-neck ensemble in line with the trunk during the movement. About half of the floppy subjects displayed reflex activation of the neck muscles on the side opposite to the direction of acceleration, which occurred before or during the head movement and tended to exaggerate it. The other floppy subjects seemed to rely on only the passive biomechanical properties of their head-neck ensemble to compensate for the perturbation. In our study, proprioception was the sole source of sensory information as long as the head did not move. We therefore presume that the EMG responses and head movements we observed were mainly triggered by the activation of stretch receptors in the hips, trunk and/or neck. The visualisation of an imaginary reference in space during sideways impulses significantly reduced the head roll exhibited by floppy subjects. This suggests that the adoption by the central nervous system of an extrinsic, 'allocentric' frame of reference instead of an intrinsic, 'egocentric' one may be instrumental for the selection of the stiff strategy. The response of floppy subjects appeared to be maladaptive and likely to increase the risk of whiplash injury during motor vehicle accidents. Evolution of postural control may not have taken into account the implications of passive, high-acceleration perturbations affecting seated subjects.
本研究的目的是确定在遭受高加速度、被动线性加速的坐姿受试者中，情境和在线感官信息是如何结合以控制姿势的。受试者闭眼坐在伺服控制的线性滑板上。他们被要求放松，并接受侧向或前后方向的短暂加速。刺激具有突然的起始，类似于轻微汽车碰撞时所经历的加速度变化率。使用Optotrak系统测量头部和身体的旋转与平移。在一些受试者中，同时记录选定颈部和/或背部肌肉的表面肌电图（EMG）反应。对于每个受试者，从第一次试验开始反应就高度定型，几乎没有习惯化或敏感化的迹象。侧向和前后加速获得了类似的结果。在每次脉冲期间，头部比躯干滞后几十毫秒。受试者的头部运动反应分布在两个极端类别之间的连续体中。“僵硬”的受试者在脉冲的整个持续时间内，头部相对于躯干几乎没有旋转或平移。相比之下，“松弛”的受试者在与滑板运动相反的方向上，头部相对于躯干表现出较大的滚动或俯仰。这种反应表现为对脉冲的夸张“惯性”反应。表面肌电图记录显示，大多数僵硬的受试者没有收缩其颈部或背部浅层肌肉。我们认为他们依靠深层轴向肌肉组织的双侧收缩，在运动过程中使头颈整体与躯干保持一致。大约一半的松弛受试者在与加速方向相反的一侧颈部肌肉出现反射性激活，这发生在头部运动之前或期间，并倾向于夸大这种运动。其他松弛受试者似乎仅依靠头颈整体的被动生物力学特性来补偿扰动。在我们的研究中，只要头部不移动，本体感觉就是感官信息的唯一来源。因此，我们推测我们观察到的肌电图反应和头部运动主要是由髋部、躯干和/或颈部的牵张感受器激活触发的。在侧向脉冲期间想象空间中的一个虚拟参考物，显著减少了松弛受试者表现出的头部滚动。这表明中枢神经系统采用外在的“异我中心”参考系而非内在的“自我中心”参考系，可能有助于选择僵硬策略。松弛受试者的反应似乎是适应不良的，并且可能会增加机动车事故中颈部挥鞭伤的风险。姿势控制的进化可能没有考虑到影响坐姿受试者的被动高加速度扰动的影响。
