Department of Psychiatry, University of Wisconsin-Madison, 53719, USA.
Brain Topogr. 2010 Jan;22(4):281-93. doi: 10.1007/s10548-009-0118-1. Epub 2009 Nov 14.
A commonly held view is that, when delivered during the performance of a task, repetitive TMS (rTMS) influences behavior by producing transient "virtual lesions" in targeted tissue. However, findings of rTMS-related improvements in performance are difficult to reconcile with this assumption. With regard to the mechanism whereby rTMS influences concurrent task performance, a combined rTMS/EEG study conducted in our lab has revealed a complex set of relations between rTMS, EEG activity, and behavioral performance, with the effects of rTMS on power in the alpha band and on alpha:gamma phase synchrony each predicting its effect on behavior. These findings suggest that rTMS influences performance by biasing endogenous task-related oscillatory dynamics, rather than creating a "virtual lesion". To further differentiate these two alternatives, in the present study we compared the effects of 10 Hz rTMS on neural activity with the results of an experiment in which rTMS was replaced with 10 Hz luminance flicker. We reasoned that 10 Hz flicker would produce widespread entrainment of neural activity to the flicker frequency, and comparison of these EEG results with those from the rTMS study would shed light on whether the latter also reflected entrainment to an exogenous stimulus. Results revealed pronounced evidence for "entrainment noise" produced by 10 Hz flicker-increased oscillatory power and inter-trial coherence (ITC) at the driving frequency, and increased alpha:gamma phase synchronization-that were nonetheless largely uncorrelated with behavior. This contrasts markedly with 10-Hz rTMS, for which the only evidence for stimulation-induced noise, elevated ITC at 30 Hz, differed qualitatively from the flicker results. Simultaneous recording of the EEG thus offers an important means of directly testing assumptions about how rTMS exerts its effects on behavior.
一种普遍的观点认为，在执行任务期间进行重复经颅磁刺激（rTMS）会通过在靶向组织中产生短暂的“虚拟损伤”来影响行为。然而，rTMS 相关的性能改善发现很难与这一假设相协调。关于 rTMS 影响并发任务性能的机制，我们实验室进行的一项 rTMS/EEG 联合研究揭示了 rTMS、EEG 活动和行为表现之间复杂的关系，rTMS 对 alpha 波段功率和 alpha:gamma 相位同步的影响都预测了其对行为的影响。这些发现表明，rTMS 通过偏向内源性与任务相关的振荡动力学来影响性能，而不是产生“虚拟损伤”。为了进一步区分这两种选择，在本研究中，我们比较了 10Hz rTMS 对神经活动的影响与 rTMS 被 10Hz 亮度闪烁取代的实验结果。我们推断，10Hz 闪烁会使神经活动广泛地与闪烁频率同步，并且将这些 EEG 结果与 rTMS 研究的结果进行比较，可以揭示后者是否也反映了对外部刺激的同步。结果显示，10Hz 闪烁产生了明显的“同步噪声”证据——增加了驱动频率的振荡功率和试验间相干性（ITC），以及增加了 alpha:gamma 相位同步——尽管这些与行为基本上没有相关性。这与 10Hz rTMS 形成鲜明对比，对于后者，唯一证明刺激诱导噪声的证据是 30Hz 时 ITC 的升高，这与闪烁结果在性质上有所不同。因此，同时记录 EEG 提供了一种直接测试关于 rTMS 如何对行为产生影响的假设的重要手段。
