Triggs W J, Cros D, Macdonell R A, Chiappa K H, Fang J, Day B J
Department of Neurology, University of Florida, Gainesville.
Brain Res. 1993 Nov 19;628(1-2):39-48. doi: 10.1016/0006-8993(93)90935-g.
We investigated the electromyographic silent period in abductor pollicis brevis (APB) and flexor carpi radialis muscles following transcranial magnetic stimulation of human motor cortex. In APB, we measured cortical stimulation silent period (CSSP) duration as a function of stimulus intensity, motor-evoked potential (MEP) amplitude and muscle twitch force. We used peri-stimulus-time histograms to study the effect of cortical stimulation on single-motor unit firing patterns. We compared F-waves, H-reflexes and magnetic MEPs elicited during the CSSP to control responses elicited at rest and during voluntary contraction. CSSP duration depended on the intensity of cortical stimulation. However, we found no relationship between CSSP duration and MEP amplitude or muscle twitch force, thus the CSSP is not dependent solely on Renshaw cell inhibition or on changes in Ia and Ib afferent activity following the cortically induced muscle twitch. At low intensities of stimulation, the interval to resumption of motor unit firing following the peak in the peri-stimulus-time histogram corresponding to MEP latency sometimes exceeded that which could be accounted for by the motor unit's firing rate prior to the stimulus, suggesting that synchronization of motor unit firing by cortical stimulation cannot account for the CSSP. We found brief inhibition of F-waves during the CSSP in some subjects, reflecting activation of inhibitory corticospinal projections or segmental effects. In contrast, we observed longer inhibition of H-reflexes during the CSSP in all subjects, perhaps resulting from presynaptic inhibition of Ia afferents. Magnetic MEPs also were inhibited during the CSSP, suggesting inhibition of cortical elements by transcranial magnetic stimulation.
我们研究了经颅磁刺激人类运动皮层后，拇短展肌（APB）和桡侧腕屈肌的肌电图静息期。在APB中，我们测量了皮层刺激静息期（CSSP）的持续时间，作为刺激强度、运动诱发电位（MEP）幅度和肌肉抽搐力的函数。我们使用刺激周围时间直方图来研究皮层刺激对单个运动单位放电模式的影响。我们比较了CSSP期间诱发的F波、H反射和磁MEP与静息和自主收缩期间诱发的对照反应。CSSP持续时间取决于皮层刺激的强度。然而，我们发现CSSP持续时间与MEP幅度或肌肉抽搐力之间没有关系，因此CSSP并非仅依赖于闰绍细胞抑制或皮层诱发肌肉抽搐后Ia和Ib传入活动的变化。在低刺激强度下，与MEP潜伏期相对应的刺激周围时间直方图峰值后运动单位放电恢复的间隔有时超过刺激前运动单位放电频率所能解释的范围，这表明皮层刺激使运动单位放电同步无法解释CSSP。我们发现一些受试者在CSSP期间F波受到短暂抑制，这反映了抑制性皮质脊髓投射的激活或节段效应。相比之下，我们观察到所有受试者在CSSP期间H反射受到更长时间的抑制，这可能是由于Ia传入纤维的突触前抑制所致。CSSP期间磁MEP也受到抑制，这表明经颅磁刺激对皮层成分有抑制作用。
