BACKGROUND A single session of anodal tDCS induces LTP-like plasticity which lasts for about one hour, while repetition of stimulation within a time interval of 30 minutes results in late-phase effects lasting for at least 24 hours with standard stimulation protocols. OBJECTIVE In this pilot study, we explored if the after-effects of a recently developed intensified single session stimulation protocol are relevantly prolonged in the motor cortex by repetition of this intervention. METHODS 16 healthy right-handed subjects participated in this study. The effects of an intensified (3mA-20min) and a standard anodal tDCS protocol (1mA-15min) with short (20 minutes) and long (3 hours) repetition intervals were compared with the effects of respective single session tDCS protocols (3mA-20min, 1mA-15min, and Sham). Cortical excitability alterations were monitored by single-pulse TMS-elicited MEPs. RESULTS Compared to sham, both single session tDCS protocols (1mA-15min, and 3mA-20min) resulted in cortical excitability enhancements lasting for about 30 minutes after stimulation. The short repetition interval (20 minutes) resulted in a prolongation of after-effects for the standard protocol, which lasted for more than 24 hours after stimulation. For the intensified protocol, the prolongation of after-effects was limited to 120 mins after stimulation. The long repetition interval (3 hours) resulted in no excitability-enhancing after-effects for the intensified, and only minor excitability enhancement within the first 30 min after the intervention for the standard protocol. CONCLUSION These results suggest a non-linearity of late-phase LTP-like plasticity induction, which was dependent not only on the interval of intervention repetition, but also on other protocol characteristics, including intensity, and duration of tDCS. Further studies in larger samples are needed to confirm these results.

中文翻译：

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通过反复阳极经颅直流电刺激诱导初级运动皮层中的长期增强样可塑性——强化方案效果更好？

背景 单次阳极 tDCS 诱导持续约一小时的 LTP 样可塑性，而在 30 分钟的时间间隔内重复刺激导致晚期效应持续至少 24 小时，使用标准刺激方案。目标在这项试点研究中，我们探讨了最近开发的强化单次刺激方案的后遗症是否通过重复这种干预在运动皮层中得到相应延长。方法 16 名健康的右手受试者参与了这项研究。将具有短（20 分钟）和长（3 小时）重复间隔的强化（3mA-20 分钟）和标准阳极 tDCS 协议（1mA-15 分钟）的效果与各自单次 tDCS 协议（3mA-20 分钟）的效果进行比较、1mA-15 分钟和假）。皮质兴奋性改变由单脉冲 TMS 引发的 MEP 监测。结果 与假手术相比，单次 tDCS 协议（1mA-15 分钟和 3mA-20 分钟）都导致皮层兴奋性增强，刺激后持续约 30 分钟。短的重复间隔（20 分钟）导致标准方案的后遗症延长，刺激后持续超过 24 小时。对于强化方案，后效的延长仅限于刺激后 120 分钟。长重复间隔（3 小时）导致没有增强兴奋性的后遗症，并且在标准协议干预后的前 30 分钟内只有轻微的兴奋性增强。结论 这些结果表明晚期 LTP 样可塑性诱导的非线性，这不仅取决于干预重复的间隔，还取决于其他协议特征，包括强度和 tDCS 的持续时间。需要对更大样本的进一步研究来证实这些结果。