Keck M E, Pijnappels M, Schubert M, Colombo G, Curt A, Dietz V
Swiss Paraplegic Center, University Hospital Balgrist, University of Zürich.
Electroencephalogr Clin Neurophysiol. 1998 Jun;109(3):215-23. doi: 10.1016/s0924-980x(98)00009-5.
The aim of this study was to evaluate the degree of contribution of supraspinal input to the generation of the compensatory leg muscle activation following stance perturbation. Therefore, evoked motor response (EMR) input-output relations of two different motor tasks were compared at 3 distinct periods: (1) the basic period of muscular activity during standing, i.e. when no additional cortical or spinal activity due to the different tasks is to be expected, (2) the pre-movement period with low background activity, when different spinal and cortical inputs to the motoneuronal pool can be assumed and (3) the period of plateau EMG activity of compensatory and voluntary motor task. Transcranial magnetic stimulation (TMS) just below the motor threshold was applied randomly at 19 different time-intervals before and during the onset of stance perturbation and for comparison during an equivalent voluntary foot-dorsiflexion task. Recordings of electromyographic (EMG) activity from the tibialis anterior (TA) and corresponding ankle-joint movements were made from both legs. Forward-directed displacements were induced by randomly-timed ramp impulses of constant acceleration upon a moveable platform. For comparison, leg muscle EMG was recorded during isometric foot dorsiflexion during stance while leaning back against a support. The stance perturbations were followed by a compensatory response (CR) in the TA with a mean onset time of 81 ms. During the basic period of muscular activity and the period of plateau EMG activity there was no significant difference of the input-output relation between stance perturbation and the voluntary motor task. However, in the voluntary task compared with the CR, there was significantly greater input-output relation (facilitation) of the EMR in the TA following TMS, which may be related to an increased cortical influence. In contrast to this result of the CR following stance perturbation, a facilitation of the EMR was described for hand muscles under corresponding conditions of automatic compensation for muscle stretch, suggesting a transcortical reflex loop. This difference in the results from upper and lower extremity muscles favors the assumption of a predominantly spinal generation of the TA-CR following stance perturbation.
本研究的目的是评估脊髓上输入对姿势扰动后代偿性腿部肌肉激活产生的贡献程度。因此，在3个不同时期比较了两种不同运动任务的诱发运动反应（EMR）输入-输出关系：（1）站立时肌肉活动的基础期，即预计不会因不同任务而产生额外皮质或脊髓活动时；（2）背景活动较低的运动前期，此时可假定有不同的脊髓和皮质输入至运动神经元池；（3）代偿性和自主性运动任务的肌电图（EMG）活动平稳期。在姿势扰动开始前和开始期间，于19个不同时间间隔随机施加略低于运动阈值的经颅磁刺激（TMS），并在等效的自主性足背屈任务期间进行比较。记录双侧胫前肌（TA）的肌电图（EMG）活动及相应的踝关节运动。在可移动平台上通过随机定时的恒定加速度斜坡脉冲诱发向前位移。作为比较，在站立时靠在支撑物上向后倾斜的同时进行等长足背屈时记录腿部肌肉的EMG。姿势扰动后TA出现代偿反应（CR），平均起始时间为81 ms。在肌肉活动基础期和平稳期EMG活动期间，姿势扰动和自主性运动任务之间的输入-输出关系无显著差异。然而，与CR相比，在自主性任务中，TMS后TA中EMR的输入-输出关系（易化）显著更大，这可能与皮质影响增加有关。与姿势扰动后CR的这一结果相反，在肌肉牵张自动代偿的相应条件下，手部肌肉的EMR出现易化，提示存在皮质下反射环。上下肢肌肉结果的这种差异支持以下假设：姿势扰动后TA-CR主要由脊髓产生。
