BACKGROUND Cortical oscillatory activities play a role in regulating several brain functions in humans. However, whether motor resonant oscillations (i.e. β and γ) modulate long-term depression (LTD)-like plasticity of the primary motor cortex (M1) is still unclear. OBJECTIVE To address this issue, we combined transcranial alternating current stimulation (tACS), a technique able to entrain cortical oscillations, with continuous theta burst stimulation (cTBS), a transcranial magnetic stimulation (TMS) protocol commonly used to induce LTD-like plasticity in M1. METHODS Motor evoked potentials (MEPs) elicited by single-pulse TMS, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated before and 5, 15 and 30 min after cTBS alone or cTBS delivered during β-tACS (cTBS-β) or γ-tACS (cTBS-γ). Moreover, we tested the effects of β-tACS (alone) on short-latency afferent inhibition (SAI) and γ-tACS on SICI in order to verify whether tACS-related interneuronal modulation contributes to the effects of tACS-cTBS co-stimulation. RESULTS cTBS-γ turned the expected after-effects of cTBS from inhibition to facilitation. By contrast, responses to cTBS-β were similar to those induced by cTBS alone. β- and γ-tACS did not change MEPs evoked by single-pulse TMS. β-tACS reduced SAI and γ-tACS reduced SICI. However, the degree of γ-tACS-induced modulation of SICI did not correlate with the effects of cTBS-γ. CONCLUSION γ-tACS reverses cTBS-induced plasticity of the human M1. γ-oscillations may therefore regulate LTD-like plasticity mechanisms.

中文翻译：

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γ-tACS 可以逆转人类初级运动皮层的 LTD 样可塑性

背景皮质振荡活动在调节人类的若干脑功能中起作用。然而，运动共振振荡（即β和γ）是否调节初级运动皮层（M1）的长期抑郁（LTD）样可塑性尚不清楚。目的为了解决这个问题，我们将经颅交流电刺激 (tACS)，一种能够夹带皮层振荡的技术，与连续θ脉冲刺激 (cTBS)，一种常用于诱导 LTD 样可塑性的经颅磁刺激 (TMS) 方案相结合。 M1。方法 在单独使用 cTBS 或在 β-tACS (cTBS) 期间递送 cTBS 之前和之后 5、15 和 30 分钟评估由单脉冲 TMS、短间隔皮质内抑制 (SICI) 和皮质内促进 (ICF) 引起的运动诱发电位 (MEP) -β) 或 γ-tACS (cTBS-γ)。而且，我们测试了 β-tACS（单独）对短延迟传入抑制（SAI）和 γ-tACS 对 SICI 的影响，以验证 tACS 相关的神经元间调节是否有助于 tACS-cTBS 共刺激的影响。结果 cTBS-γ 将 cTBS 的预期后效从抑制转变为促进。相比之下，对 cTBS-β 的反应与单独由 cTBS 诱导的反应相似。β- 和 γ-tACS 没有改变单脉冲 TMS 诱发的 MEP。β-tACS 降低 SAI，γ-tACS 降低 SICI。然而，γ-tACS 诱导的 SICI 调制程度与 cTBS-γ 的影响无关。结论 γ-tACS 逆转 cTBS 诱导的人类 M1 可塑性。因此，γ 振荡可能会调节类似 LTD 的可塑性机制。