Kaneko K, Kawai S, Fuchigami Y, Shiraishi G, Ito T
Department of Orthopedic Surgery, University of Yamaguchi, School of Medicine, Japan.
J Neurol Sci. 1996 Jul;139(1):131-6.
Following magnetic transcranial stimulation, motor-evoked potentials (MEPs) from the abductor digiti minimi muscle, and evoked spinal cord potentials (ESCPs) from the cervical epidural space were recorded simultaneously in 9 subjects in the awake and anesthetized condition. In the awake condition, during voluntary contraction, one (n = 5) or two (n = 4) components of the ESCPs were elicited at the threshold stimulus intensity of the MEPs. As the stimulus intensity increased, an early response (n = 7) and multiple late components were recorded. The first component at high stimulus output (average 80%) preceded the small potentials elicited at threshold stimulus intensity. The latency of each component of the ESCPs during voluntary contraction was the same as that during the resting condition. In addition, the enhancement of amplitude of the ESCPs during voluntary contraction was not significant compared with that recorded at rest. During general anesthesia with volatile anesthetics, the first component of the ESCPs could be elicited at high stimulus intensity, but later components were markedly attenuated. In paired transcranial magnetic stimulation, the amplitude of this first potential following the test stimulus completely recovered within the 2 ms interstimulus interval. From these results, we hypothesized that the first component was generated non-synaptically (D-wave), but later components were generated transsynaptically (I-waves). Compound muscle action potentials (CMAPs) and F-waves also were recorded following supramaximal ulnar nerve stimulation at the wrist. Peripheral conduction time, which included synaptic delay in spinal motor neurons, was measured as follows (latency of CMAPs+ latency of F-wave + 1)/2 (ms). The central motor conduction time (CMCT) was measured by subtracting the peripheral conduction time from the onset latency of the MEP at high stimulus intensity in the awake state. During voluntary contraction, the calculated CMCT (4.9 +/- 1.0 ms) was the same as the onset latency of the second component of the ESCPs (I-wave, 4.3 +/- 0.2 ms) recorded from the C6-C6/7 epidural space. These results suggest that transcranial magnetic stimulation generates I-waves preferentially when the stimulus intensity was set at just the threshold level of the MEPs during voluntary contraction in the awake condition. At high stimulus intensity, transcranial magnetic stimulation can elicit both D- and I-waves, but most spinal cells require I-wave activation to fire. Facilitatory effects of voluntary contraction on the muscle response following transcranial magnetic stimulation mainly originates at a spinal level.
在9名受试者处于清醒和麻醉状态时，同步记录了磁刺激经颅刺激后小指展肌的运动诱发电位（MEP）以及颈段硬膜外间隙的脊髓诱发电位（ESCP）。在清醒状态下，自主收缩时，在MEP的阈刺激强度下可引出ESCP的一个成分（n = 5）或两个成分（n = 4）。随着刺激强度增加，可记录到一个早期反应（n = 7）和多个晚期成分。高刺激输出时的第一个成分（平均80%）先于阈刺激强度时引出的小电位。自主收缩时ESCP各成分的潜伏期与静息状态时相同。此外，与静息时记录的相比，自主收缩时ESCP的波幅增强不显著。在使用挥发性麻醉剂进行全身麻醉期间，ESCP的第一个成分可在高刺激强度时引出，但晚期成分明显衰减。在配对经颅磁刺激中，测试刺激后的第一个电位的波幅在2毫秒的刺激间隔内完全恢复。根据这些结果，我们推测第一个成分是非突触性产生的（D波），但晚期成分是经突触产生的（I波）。在腕部对尺神经进行超强刺激后，还记录了复合肌肉动作电位（CMAP）和F波。外周传导时间（包括脊髓运动神经元中的突触延迟）的测量方法如下：（CMAP潜伏期+ F波潜伏期+ 1）/2（毫秒）。中枢运动传导时间（CMCT）通过从清醒状态下高刺激强度时MEP的起始潜伏期减去外周传导时间来测量。自主收缩时，计算出的CMCT（4.9±1.0毫秒）与从C6 - C6/7硬膜外间隙记录到的ESCP第二个成分（I波，4.3±0.2毫秒）的起始潜伏期相同。这些结果表明，在清醒状态下自主收缩时，当刺激强度设定为刚好是MEP的阈水平时，经颅磁刺激优先产生I波。在高刺激强度时，经颅磁刺激可引出D波和I波，但大多数脊髓细胞需要I波激活才能放电。自主收缩对经颅磁刺激后肌肉反应的促进作用主要起源于脊髓水平。
