Levit-Binnun Nava, Handzy Nestor Z, Peled Avi, Modai Ilan, Moses Elisha
The Weizmann Institute of Science, Rehovot, Israel.
J Cogn Neurosci. 2007 May;19(5):721-33. doi: 10.1162/jocn.2007.19.5.721.
We study the interplay between motor programs and their timing in the brain by using precise pulses of transcranial magnetic stimulation (TMS) applied to the primary motor cortex. The movement of the finger performing a tapping task is periodically perturbed in synchronization with a metronome. TMS perturbation can profoundly affect both the finger trajectory and its kinematics, but the tapping accuracy itself is surprisingly not affected. The motion of the finger during the TMS perturbation can be categorized into two abnormal behaviors that subjects were unaware of: a doubling of the frequency of the tap and a stalling of the finger for half the period. More stalls occurred as the tapping frequency increased. In addition, an enhancement of the velocity of the finger on its way up was observed. We conclude that the timing process involved in controlling the tapping movement is separate from the motor processes in charge of execution of the motor commands. We speculate that the TMS is causing a release of the motor plan ahead of time into activation mode. The observed doubles and stalls are then the result of an indirect interaction in the brain, making use of an existing motor plan to correct the preactivation and obtain the temporal goal of keeping the beat.
我们通过对初级运动皮层施加精确的经颅磁刺激（TMS）脉冲，来研究大脑中运动程序及其时间安排之间的相互作用。执行敲击任务的手指运动与节拍器同步受到周期性干扰。TMS干扰会深刻影响手指轨迹及其运动学，但令人惊讶的是敲击精度本身并未受到影响。TMS干扰期间手指的运动可分为两种受试者未意识到的异常行为：敲击频率加倍以及手指在半个周期内停顿。随着敲击频率增加，停顿现象更多。此外，还观察到手指向上运动时速度有所增强。我们得出结论，控制敲击运动所涉及的时间安排过程与负责执行运动指令的运动过程是分开的。我们推测TMS导致运动计划提前释放到激活模式。观察到的频率加倍和停顿现象是大脑中一种间接相互作用的结果，利用现有的运动计划来校正预激活并实现保持节拍的时间目标。
