EVOKED EMG of THE MASTICATORY MUSCLES by TRANSCRANIAL MAGNETIC STIMULATION IN MAN

用经颅磁刺激方法，对人咬肌外周或中枢诱发的肌电反应进行了分析。将刺激线圈的中心沿颅骨轮廓置于距颅顶沿着下外侧9 cm处，从同侧咬肌诱发了4种反应。将线圈中心分别置于距头顶外侧3 ~ 5.5cm和前方2.5cm处，从对侧咬肌记录到两种反应，同侧反应的潜伏期依次为6 msec、10- 13 msec和2- 3 msec。这些反应被认为分别是M波、与肢体肌肉S波相对应的波、皮层驱动的波和H波，对侧反应的潜伏期分别为11- 13毫秒和23毫秒。前者最可能是由皮层驱动的I波（Amassian：1987）或D波（Edyly：1990），当刺激在咀嚼口香糖时无预期地施加时，中风的周期时间显著延长，随后2-3次中风的节律变得不稳定。这被认为是由于皮层刺激对节律发生器的干扰的影响。通过磁刺激，咬肌肌电图上出现了一个不完全的抑制相，潜伏期约为80毫秒。这种长潜伏期的抑制可能与大脑皮层有关。

Using a transcranial magnetic stimulation, peripherally or centrally induced responses of the masseter muscle were electromyographically analized in man.By positioning the center of a stimulating coil at 9cm far inferolaterally from the vertex along a contour of the skull, four responses were induced from the ipsilateral masseter muscle. Other two responses were recorded from the contralatera masseter muscle by positioning the coil center at 3-5.5cm laterally and 2.5cm anteroirly from the vertex.latencies of the ipsilateral responses were 6msec, 10-13msec and 2-3msec in the order of threshold level. These responses were thought to be M-wave, a wave corresponding to S-wave in the extremity muscles, one drived from the cortex, and H-wave, respectively.Latencies of the contralateral responses were 11-13msec and 23msec. The former is the most likely to be I-wave (Amassian : 1987) drived from the cortex, or D-wave (Edyly : 1990).When the stimulus was applied during a gum-chewing without any expectations, a cycle time of the stroke was remarkably prolonged, and the rhythm of following 2-3 strokes became unstable. This is thought to e an effect of the disturbance on a rhythm generator due to cortical stimulation.By magnetic stimulation, an incomplete depression phase appeared on the masseter EMG with a latency of approximately 80msec. This long-latency depression might related to the cortex in the orign.