Di Lazzaro V, Restuccia D, Oliviero A, Profice P, Ferrara L, Insola A, Mazzone P, Tonali P, Rothwell J C
Istituto di Neurologia, Università Cattolica, Rome, Italy.
Exp Brain Res. 1998 Mar;119(2):265-8. doi: 10.1007/s002210050341.
A magnetic transcranial conditioning stimulus given over the motor cortex at intensities below threshold for obtaining electromyographical (EMG) responses in active hand muscles can suppress responses evoked in the same muscles at rest by a suprathreshold magnetic test stimulus given 1-5 ms later. In order to define the mechanism of this inhibitory effect, we recorded descending volleys produced by single and paired magnetic transcranial stimulation of motor cortex through high cervical, epidural electrodes implanted for pain relief in two conscious subjects with no abnormality of the central nervous system. The conditioning stimulus evoked no recognisable descending activity in the spinal cord, whilst the test stimulus evoked 3-4 waves of activity (I-waves). Conditioning stimulation suppressed the size of both the descending spinal cord volleys and the EMG responses evoked by the test stimulus. Inhibition of the descending spinal volleys was most pronounced at ISI 1 ms and had disappeared by ISI 5 ms. It was evident for all components following the I1-wave, while the I1-wave itself was not inhibited at all. We conclude that a small conditioning magnetic stimulus can suppress the excitability of human motor cortex, probably by activating local corticocortical inhibitory circuits.
在主动手部肌肉中，给予运动皮层低于引发肌电图（EMG）反应阈值强度的磁经颅条件刺激，可抑制1-5毫秒后给予的阈上磁测试刺激在同一肌肉静息时诱发的反应。为了确定这种抑制作用的机制，我们通过植入高位颈段硬膜外电极记录了两名中枢神经系统无异常的清醒受试者在接受单次和配对磁经颅刺激运动皮层时产生的下行冲动，这些电极是为缓解疼痛而植入的。条件刺激在脊髓中未诱发可识别的下行活动，而测试刺激诱发了3-4波活动（I波）。条件刺激抑制了下行脊髓冲动的大小以及测试刺激诱发的EMG反应。下行脊髓冲动的抑制在刺激间隔（ISI）为1毫秒时最为明显，在ISI为5毫秒时消失。对于I1波之后的所有成分都有明显抑制，而I1波本身完全未被抑制。我们得出结论，小的条件磁刺激可能通过激活局部皮质-皮质抑制回路来抑制人类运动皮层的兴奋性。
