Eichenberger A, Rüegg D G
J Physiol. 1984 Feb;347:545-59. doi: 10.1113/jphysiol.1984.sp015082.
In a reaction-time situation, the monosynaptic spinal reflex (H reflex) is facilitated before the onset of an electromyographic (e.m.g.) response. The aim of the present investigation was to study aspects of this facilitation. Human subjects were required to perform isometric plantarflexions of the foot in response to a visual stimulus. The movement was always on the same side in the simple reaction-time situation, and randomly with the right or left foot in the choice reaction-time situation. Stimuli to evoke H reflexes were applied bilaterally 40-400 ms after the onset of the visual stimulus. Pre-motor time, i.e. the interval between the onset of the visual stimulus and the e.m.g. response, and reaction time, i.e. the interval between the onset of the visual stimulus and the response on the torque recording, were computed. In both reaction-time situations, there was a significant facilitation of the ipsilateral H reflex 100-160 ms before e.m.g. onset and, in some subjects, a small facilitation of the contralateral H reflex. The specific facilitation, i.e. the difference between the facilitation on the ipsi- and contralateral side relative to the movement, was not significantly different on the right and left side. Pre-motor time was divided into the interval from the light onset until the onset of the specific facilitation, and the interval from the onset of the facilitation until the onset of the voluntary response. Both intervals increased, and the slope and the amplitude of the facilitation decreased with increasing pre-motor time and reaction time. The specificity of the H reflex facilitation in a choice reaction-time situation implies that the interval from light onset until the onset of the facilitation includes stimulus identification and response selection, and the interval from the onset of the facilitation until the e.m.g. response preparation of the motor system for the required movement. The present results suggest that the specific facilitation of the H reflex before a movement is caused by removal of presynaptic inhibition at I a terminals or by activation of interneurones intercalated in polysynaptic components of the H reflex rather than by a subthreshold activation of motoneurones.
在反应时的情况下，单突触脊髓反射（H反射）在肌电图（e.m.g.）反应开始之前就得到了易化。本研究的目的是探讨这种易化的各个方面。要求人类受试者对视觉刺激做出足部等长跖屈反应。在简单反应时情况下，动作总是在同一侧进行，而在选择反应时情况下，则随机用右脚或左脚进行。在视觉刺激开始后40 - 400毫秒双侧施加诱发H反射的刺激。计算运动前时间，即视觉刺激开始到e.m.g.反应之间的间隔，以及反应时间，即视觉刺激开始到扭矩记录上的反应之间的间隔。在两种反应时情况下，在e.m.g.开始前100 - 160毫秒同侧H反射有显著易化，并且在一些受试者中，对侧H反射有轻微易化。特定易化，即相对于动作同侧和对侧易化之间的差异，在左右两侧没有显著差异。运动前时间被分为从光刺激开始到特定易化开始的间隔，以及从易化开始到自主反应开始的间隔。随着运动前时间和反应时间的增加，这两个间隔都增加，并且易化的斜率和幅度减小。选择反应时情况下H反射易化的特异性意味着从光刺激开始到易化开始的间隔包括刺激识别和反应选择，以及从易化开始到e.m.g.反应的间隔包括运动系统为所需动作做准备。目前的结果表明，运动前H反射的特定易化是由Ia终末突触前抑制的解除或H反射多突触成分中介入的中间神经元的激活引起的，而不是由运动神经元的阈下激活引起的。
