Blouin Jean-Sébastien, Siegmund Gunter P, Timothy Inglis J
School of Human Kinetics, University of British Columbia, Vancouver, Canada.
J Appl Physiol (1985). 2007 Apr;102(4):1574-86. doi: 10.1152/japplphysiol.00703.2006. Epub 2006 Dec 14.
Postural and startle responses rapidly habituate with repeated exposures to the same stimulus, and the first exposure to a seated forward acceleration elicits a startle response in the neck muscles. Our goal was to examine how the acoustic startle response is integrated with the habituated neck postural response elicited by forward accelerations of seated subjects. In experiment 1, 14 subjects underwent 11 sequential forward accelerations followed by 5 additional sled accelerations combined with a startling tone (124-dB sound pressure level) initiated 18 ms after sled acceleration onset. During the acceleration-only trials, changes consistent with habituation occurred in the root-mean-square amplitude of the neck muscles and in the peak amplitude of five head and torso kinematic variables. The subsequent addition of the startling tone restored the amplitude of the neck muscles and four of the five kinematic variables but shortened onset of muscle activity by 9-12 ms. These shortened onset times were further explored in experiment 2, wherein 16 subjects underwent 11 acceleration-only trials followed by 15 combined acceleration-tone trials with interstimulus delays of 0, 13, 18, 23, and 28 ms. Onset times shortened further for the 0- and 13-ms delays but did not lengthen for the 23- and 28-ms delays. These temporal and spatial changes in EMG can be explained by a summation of the excitatory drive converging at or before the neck muscle motoneurons. The present observations suggest that habituation to repeated sled accelerations involves extinguishing the startle response and tuning the postural response to the whole body disturbance.
姿势和惊吓反应会随着对相同刺激的反复暴露而迅速习惯化，并且首次暴露于坐姿向前加速会引发颈部肌肉的惊吓反应。我们的目标是研究听觉惊吓反应如何与坐姿受试者向前加速引发的习惯化颈部姿势反应相结合。在实验1中，14名受试者接受了11次连续的向前加速，随后是5次额外的雪橇加速，并在雪橇加速开始后18毫秒启动一个惊吓音调（124分贝声压级）。在仅加速试验期间，颈部肌肉的均方根振幅以及五个头部和躯干运动学变量的峰值振幅出现了与习惯化一致的变化。随后添加的惊吓音调恢复了颈部肌肉的振幅以及五个运动学变量中的四个，但肌肉活动的起始时间缩短了9 - 12毫秒。在实验2中进一步探究了这些缩短的起始时间，其中16名受试者接受了11次仅加速试验，随后是15次联合加速 - 音调试验，刺激间隔延迟分别为0、13、18、23和28毫秒。对于0毫秒和13毫秒的延迟，起始时间进一步缩短，但对于23毫秒和28毫秒的延迟没有延长。肌电图的这些时间和空间变化可以通过在颈部肌肉运动神经元处或之前汇聚的兴奋性驱动的总和来解释。目前的观察结果表明，对重复雪橇加速的习惯化涉及消除惊吓反应并调整对全身干扰的姿势反应。
