Jennum P, Winkel H, Fuglsang-Frederiksen A
Department of Clinical Neurophysiology, Hvidovre Hospital, University of Copenhagen, Denmark.
Electromyogr Clin Neurophysiol. 1996 Sep;36(6):341-8.
We studied the effect of varying interstimulus intervals (ISI) on the motor evoked potentials (MEP) using paired transcranial magnetic stimulation (PTMS) during relaxation and voluntary contraction of the abductor pollicis brevis. At ISI > or = 10 ms two independent MEPs could be evoked. At ISIs between 12-30 ms the amplitudes of the MEPs evoked by the second (test) stimuli had larger amplitude and shorter latencies than the MEPs evoked by the first (conditioning) stimuli. At an ISI of 50 ms the second MEP were similar to the first, between 75 and 100 ms the second MEPs were inhibited and at ISI of 200 and 400 ms the second MEPs showed almost similar amplitudes and latencies compared to the first. During voluntary contraction, the amplitudes of the first MEPs was higher compared to relaxed responses. The amplitudes of the second MEPs showed a similar pattern as the relaxed responses, but with a relatively smaller increase between 12-30 ms (p < 0.01), and less inhibition at 75 and 100 ms (p < 0.01). The study shows that conditioning stimuli 12-30 ms before the test stimulus facilitates the second MEP, and an ISI between 75-100 ms inhibit the second MEP. Voluntary contraction exerts a facilatory effect and reduce inhibition in the corticospinal neurons. These findings may reflects the changes in excitability and inhibition in the cortico-spinal neurons.
我们使用配对经颅磁刺激（PTMS）研究了不同刺激间隔（ISI）对拇短展肌在放松和自主收缩期间运动诱发电位（MEP）的影响。当ISI≥10 ms时，可诱发两个独立的MEP。当ISI在12 - 30 ms之间时，由第二个（测试）刺激诱发的MEP的振幅比由第一个（条件）刺激诱发的MEP更大，潜伏期更短。当ISI为50 ms时，第二个MEP与第一个相似，在75至100 ms之间第二个MEP受到抑制，当ISI为200和400 ms时，第二个MEP与第一个相比显示出几乎相似的振幅和潜伏期。在自主收缩期间，第一个MEP的振幅比放松反应时更高。第二个MEP的振幅显示出与放松反应相似的模式，但在12 - 30 ms之间增加相对较小（p < 0.01），在75和100 ms时抑制作用较小（p < 0.01）。该研究表明，在测试刺激前12 - 30 ms的条件刺激可促进第二个MEP，而75 - 100 ms之间的ISI会抑制第二个MEP。自主收缩发挥促进作用并减少皮质脊髓神经元的抑制。这些发现可能反映了皮质脊髓神经元兴奋性和抑制性的变化。
