Müller K, Schmitz F, Schnitzler A, Freund H J, Aschersleben G, Prinz W
Heinrich-Heine University, Düsseldorf, Germany.
J Cogn Neurosci. 2000 Jul;12(4):546-55. doi: 10.1162/089892900562282.
Sensorimotor synchronization tasks, in which subjects have to tap their finger in synchrony with an isochronous auditory click, typically reveal a synchronization error with the tap preceding the click by about 20 to 50 msec. Although extensive behavioral studies and a number of different explanatory accounts have located the cause of this so-called "negative asynchrony" on different levels of processing, the underlying mechanisms are still not completely understood. Almost nothing is known about the central processes, in particular, which sensory or motor events are synchronized by subjects. The present study examined central-level processing in synchronization tasks with magnetoencephalography (MEG). Eight subjects synchronized taps with their right index finger to an isochronous binaural pacing signal presented at an interstimulus interval of 800 msec. To gain information on central temporal coupling between "tap" and "click," evoked responses were averaged time-locked to the auditory signal and the tap onset. Tap-related responses could be explained with a three dipole model: One source, peaking at approximately 77 msec before tap onset, was localized in contralateral primary motor cortex (MI); the two other sources, peaking approximately at tap onset and 75 msec after tap onset, in contralateral primary somatosensory cortex (SI). Temporal coupling of these sources was compared in relation to different trigger points. The second SI source was equally well time-locked to the tap and to the auditory click. Furthermore, analysis of the time locking of this source activity as a function of the temporal order of tap and click showed that the second event - irrespective whether tap or click - was decisive in triggering the second SI source. This suggests that subjects use mainly sensory feedback in judging and evaluating whether they are "keeping time."
感觉运动同步任务要求受试者将手指敲击与等时的听觉滴答声同步，通常会显示出敲击比滴答声提前约20至50毫秒的同步误差。尽管广泛的行为研究和许多不同的解释性说明已在不同处理水平上找到了这种所谓“负异步”的原因，但其潜在机制仍未完全理解。关于中枢过程几乎一无所知，特别是受试者同步的是哪些感觉或运动事件。本研究使用脑磁图（MEG）检查了同步任务中的中枢水平处理。八名受试者用右手食指将敲击与以800毫秒的刺激间隔呈现的等时双耳起搏信号同步。为了获取有关“敲击”和“滴答声”之间中枢时间耦合的信息，将诱发反应与听觉信号和敲击开始时间锁定后进行平均。与敲击相关的反应可以用一个三偶极子模型来解释：一个源在敲击开始前约77毫秒达到峰值，位于对侧初级运动皮层（MI）；另外两个源分别在敲击开始时和敲击开始后75毫秒达到峰值，位于对侧初级体感皮层（SI）。比较了这些源在不同触发点的时间耦合情况。第二个SI源与敲击和听觉滴答声的时间锁定情况同样良好。此外，对该源活动的时间锁定作为敲击和滴答声时间顺序的函数进行分析表明，第二个事件——无论敲击还是滴答声——在触发第二个SI源方面起决定性作用。这表明受试者在判断和评估自己是否“保持时间同步”时主要使用感觉反馈。
