Topka H, Mescheriakov S, Boose A, Kuntz R, Hertrich I, Seydel L, Dichgans J, Rothwell J
Departments of Neurology and Neuroradiology, University of Tübingen, Germany.
Brain. 1999 Aug;122 ( Pt 8):1551-62. doi: 10.1093/brain/122.8.1551.
Trains of repetitive transcranial magnetic stimulation (TMS) at 10-30 Hz and intensities of 90-120% motor threshold were delivered through a figure of eight coil over the motor cortex while normal subjects made either rapid, self-terminated (ballistic) wrist movements or maintained the position of their wrist at a fixed angle. Movement kinematics and EMG activity in antagonistic forearm muscles were analysed. In the ballistic task, repetitive TMS had little effect on the velocity or acceleration of the initial segment of the movement, although it induced large terminal oscillations (tremor) around the target position at frequencies between 4.4 and 7.2 Hz. The likelihood that tremor would occur increased with increasing stimulus intensities or frequencies. It was maximal with stimulation over the forearm area, and decreased with stimulation over the leg area, or over parietal sites; there was no tremor during stimulation of cervical nerve roots. The frequency of the induced tremor was independent of the rate of stimulation and did not depend on the presence of excitatory and inhibitory motor responses to the stimulus. Stimulation could also induce tremor of the same frequency in the fixed task, but only during co-contraction of forearm muscles. The amplitude of tremor was proportional to the level of co-contraction. Clinically, the tremor induced by repetitive TMS appeared very similar to cerebellar tremors. In order to confirm this we investigated two cerebellar patients, one with autosomal dominant cerebellar ataxia and the other with multiple sclerosis. Both of them had a terminal tremor of 6-7 Hz in the wrist movement task. In the holding task, the amplitude of their postural tremor increased with the level of co-contraction in forearm muscles. Since the frequency of repetitive TMS-induced tremor was independent of stimulus parameters, we conclude that it represents some intrinsic property of the CNS. We suggest that the tremor is caused by disruption of cortical processes involved in terminating a voluntary movement or maintaining a posture. Similarities to cerebellar patients suggest that repetitive TMS may cause tremor by interfering with adaptive cerebellar afferent inflow to motor cortex. Repetitive TMS-induced tremor, therefore, may represent a model of some forms of cerebellar tremor in man.
在正常受试者进行快速、自我终止（弹道式）腕部运动或保持腕部处于固定角度的姿势时，通过置于运动皮层上方的8字形线圈，施加频率为10 - 30Hz、强度为运动阈值90% - 120%的重复经颅磁刺激（TMS）脉冲序列。分析了运动学以及拮抗的前臂肌肉的肌电图活动。在弹道式任务中，重复TMS对运动起始段的速度或加速度影响很小，尽管它会在目标位置周围诱发频率介于4.4至7.2Hz之间的大幅度终末振荡（震颤）。震颤发生的可能性随刺激强度或频率的增加而增大。在前臂区域进行刺激时震颤最为明显，在腿部区域或顶叶部位进行刺激时震颤减弱；刺激颈神经根时不出现震颤。诱发震颤的频率与刺激速率无关，也不依赖于对刺激的兴奋性和抑制性运动反应的存在。在固定任务中，刺激也能诱发相同频率的震颤，但仅在前臂肌肉共同收缩时出现。震颤的幅度与共同收缩的程度成正比。临床上，重复TMS诱发的震颤与小脑震颤非常相似。为了证实这一点，我们研究了两名小脑疾病患者，一名患有常染色体显性遗传性小脑共济失调，另一名患有多发性硬化症。他们两人在腕部运动任务中均出现了6 - 7Hz的终末震颤。在保持任务中，他们姿势性震颤的幅度随前臂肌肉共同收缩程度的增加而增大。由于重复TMS诱发震颤的频率与刺激参数无关，我们得出结论，它代表了中枢神经系统的某种内在特性。我们认为，震颤是由参与终止自主运动或维持姿势的皮层过程受到干扰所致。与小脑疾病患者的相似性表明，重复TMS可能通过干扰小脑向运动皮层的适应性传入信息流而导致震颤。因此，重复TMS诱发的震颤可能代表了人类某些形式小脑震颤的模型。
