Wilson S A, Lockwood R J, Thickbroom G W, Mastaglia F L
Department of Medicine, University of Western Australia, Nedlands.
J Neurol Sci. 1993 Feb;114(2):216-22. doi: 10.1016/0022-510x(93)90301-e.
Transcranial magnetic stimulation (TMS) of the motor cortex during tonic muscle contraction produces a motor evoked potential followed by a silent period in the electromyogram. We sought to characterize the TMS induced silent period and to compare it to the silent period induced by supramaximal peripheral nerve stimulation. TMS was delivered to the motor cortex using a 9 cm diameter circular coil and the surface electromyogram was recorded from the contralateral abductor pollicis brevis muscle in six normal subjects. Increasing TMS stimulus intensity from 10 to 50% above threshold resulted in an increase in the duration of the silent period from a mean of 50 ms to 185 ms. Increasing the level of tonic muscle contraction from 5% of maximum to maximum resulted in a decrease in silent period duration from a mean of 155 ms to 133 ms. In contrast, the duration of the silent period following supramaximal median nerve stimulation showed greater shortening under similar conditions, from a mean of 160 ms at 5% of maximum contraction to 99 ms at 75% of maximum contraction. The TMS induced silent period was present during a TMS induced increase in the reaction time for a ballistic movement, the onset of movement being delayed until the end of the silent period. Peripheral nerve stimulation did not produce a delay in movement onset. The present findings favour a cortical origin for the TMS induced silent period, probably on the basis of intracortical inhibition, rather than peripheral inhibition of spinal motoneurones which is considered to be the basis for the silent period following peripheral nerve stimulation.
在肌肉强直性收缩期间对运动皮层进行经颅磁刺激（TMS）会产生运动诱发电位，随后在肌电图中出现静息期。我们试图对TMS诱导的静息期进行特征描述，并将其与超强外周神经刺激诱导的静息期进行比较。使用直径9厘米的圆形线圈对6名正常受试者的运动皮层进行TMS刺激，并从对侧拇短展肌记录表面肌电图。将TMS刺激强度从阈值以上10%增加到50%，导致静息期持续时间从平均50毫秒增加到185毫秒。将强直性肌肉收缩水平从最大收缩力的5%增加到最大收缩力，导致静息期持续时间从平均155毫秒减少到133毫秒。相比之下，在类似条件下，超强正中神经刺激后的静息期持续时间缩短更为明显，从最大收缩力5%时的平均160毫秒缩短到最大收缩力75%时的99毫秒。在TMS诱导的弹道运动反应时间增加期间，TMS诱导的静息期存在，运动开始延迟到静息期结束。外周神经刺激并未导致运动开始延迟。目前的研究结果支持TMS诱导的静息期起源于皮层，可能是基于皮层内抑制，而不是外周神经刺激后静息期所认为的脊髓运动神经元的外周抑制。
