Roick H, von Giesen H J, Benecke R
Department of Neurology, Heinrich-Heine-Universität, Düsseldorf, Germany.
Exp Brain Res. 1993;94(3):489-98. doi: 10.1007/BF00230207.
Non-invasive transcranial magnetic stimulation (TMS) of motor cortex induces motor evoked potentials in contralateral muscles which are thought to be conducted by the corticospinal tract. Furthermore, inhibitory actions can be elicited by TMS which appear directly after the motor evoked potential (postexcitatory inhibition, PI) and can be visualized by blockade of tonic voluntary EMG activity. It was the aim of the present study to answer the questions of whether this inhibitory action is mainly of cortical or of spinal origin, which brain area generates this inhibition, and whether the duration of PI differs between proximal and distal muscles. Experiments were performed on a total of 34 healthy volunteers. Brain stimuli were delivered with a Novametrix Magstim 200HP with a maximum output of 2.0 T, and stimulation was performed during tonic voluntary activation of the muscle under study. Stimulation strength was 1.5 times threshold level. Duration of PI was defined as the time from the onset of the motor evoked potential to the reoccurrence of the EMG background activity. PI was found more pronounced in distal hand muscles than in proximal arm and leg muscles. The largest PI values were observed when the primary motor cortex was stimulated. To test the excitability of the spinal motoneurones during PI, cortical double stimulation at various intervals was performed and the soleus H-reflex was evoked at different intervals after cortical stimulation. Neither test revealed a decrease in the excitability of the spinal motoneurones during PI. These findings imply that spinal segmental inhibitory action cannot account for PI and that, most probably, inhibitory actions within the motor cortex play a major role in the genesis of PI.
对运动皮层进行无创性经颅磁刺激（TMS）可在对侧肌肉中诱发运动诱发电位，这些电位被认为是由皮质脊髓束传导的。此外，TMS可引发抑制作用，该作用在运动诱发电位之后直接出现（兴奋后抑制，PI），并且可通过阻断持续性随意肌电图活动来显示。本研究的目的是回答以下问题：这种抑制作用主要源于皮层还是脊髓，哪个脑区产生这种抑制，以及PI的持续时间在近端和远端肌肉之间是否存在差异。总共对34名健康志愿者进行了实验。使用最大输出为2.0 T的诺瓦梅克斯Magstim 200HP进行脑刺激，并在对所研究肌肉进行持续性随意激活期间进行刺激。刺激强度为阈值水平的1.5倍。PI的持续时间定义为从运动诱发电位开始到肌电图背景活动再次出现的时间。发现PI在手部远端肌肉中比在手臂和腿部近端肌肉中更为明显。当刺激初级运动皮层时观察到最大的PI值。为了测试PI期间脊髓运动神经元的兴奋性，以不同间隔进行皮层双重刺激，并在皮层刺激后的不同间隔诱发比目鱼肌H反射。两项测试均未显示PI期间脊髓运动神经元的兴奋性降低。这些发现表明，脊髓节段性抑制作用不能解释PI，并且很可能运动皮层内的抑制作用在PI的产生中起主要作用。
