Shupert C L, Horak F B
R. S. Dow Neurological Sciences Institute, Portland, OR 97209, USA.
J Vestib Res. 1996 Nov-Dec;6(6):423-37.
Control of head position during postural responses is important to facilitate both the interpretation of vestibular signals and the stabilization of gaze. In these experiments, we compared head stabilization for two different postural tasks: 1) in response to perturbations at the head, and 2) in response to perturbations induced at the support surface, which perturb both body and head position. To determine whether normal vestibular function is necessary for head stabilization in these two tasks, responses to forward and backward mechanical perturbations of the head and body were compared for 13 normal subjects and 4 patients with profound bilateral vestibular loss (two with vestibular loss in adulthood and two in infancy). Normal subjects showed little neck muscle activity for body perturbations, but large, early activations in both neck extensors and flexors for head perturbations. In contrast, vestibular patients showed excessive neck muscle activation for body perturbations and reduced or absent neck muscle activity for head perturbations. Patients with vestibular loss in adulthood also showed increased head acceleration in response to both head and body perturbations, but patients with vestibular loss in infancy showed more normal head accelerations. For body perturbations, the differences in head acceleration between patients and normals were greater for later head acceleration peaks, indicating poor head control during the execution of the postural response. Trunk angle changes were also higher in the patients for forward body perturbations, indicating that poorer control of trunk position could have contributed to their poorer head stabilization. These results indicate that the vestibular system plays an important role in head and trunk stabilization for both head and body perturbations. However, the more normal head accelerations of the patients with infant vestibular loss also indicate that other mechanisms, possibly involving neck reflexes, can at least partially substitute for the vestibular system to provide head and trunk stabilization.
在姿势反应过程中控制头部位置对于促进前庭信号的解读和稳定注视都很重要。在这些实验中，我们比较了两种不同姿势任务下的头部稳定情况：1）对头部扰动的反应，以及2）对支撑面诱发的扰动的反应，支撑面的扰动会同时影响身体和头部位置。为了确定正常的前庭功能对于这两项任务中的头部稳定是否必要，我们比较了13名正常受试者和4名双侧前庭功能严重丧失患者（两名成年期前庭丧失患者和两名婴儿期前庭丧失患者）对头部和身体向前和向后机械扰动的反应。正常受试者在身体受到扰动时颈部肌肉活动很少，但在头部受到扰动时，颈部伸肌和屈肌都会出现强烈的早期激活。相比之下，前庭功能障碍患者在身体受到扰动时颈部肌肉激活过度，而在头部受到扰动时颈部肌肉活动减少或缺失。成年期前庭丧失的患者在头部和身体受到扰动时头部加速度也会增加，但婴儿期前庭丧失的患者头部加速度更接近正常。对于身体扰动，患者和正常受试者之间头部加速度的差异在后期头部加速度峰值时更大，这表明在姿势反应执行过程中头部控制较差。在患者中，向前身体扰动时躯干角度变化也更大，这表明躯干位置控制较差可能导致了他们较差的头部稳定。这些结果表明，前庭系统在头部和身体受到扰动时的头部和躯干稳定中起着重要作用。然而，婴儿期前庭丧失患者更接近正常的头部加速度也表明，其他机制，可能涉及颈部反射，至少可以部分替代前庭系统来提供头部和躯干稳定。
