Background

Advances in the control of transcranial magnetic stimulation (TMS) have enabled greater randomisation of stimulus intensity. It is unclear if such randomisation improves assessments of corticospinal excitability.

New Method

We recorded the amplitude of TMS-induced motor evoked potentials (MEPs) from the first dorsal interosseous muscle of eleven participants, during three TMS protocols: blocks of increasing intensity (IB), randomised blocks (RB) and inter-stimulus randomisation (IR). Stimulus intensities from 90-140% of active motor threshold described corticospinal input-output (I/O) properties. The experiment was repeated in five participants.

Results

Although MEP amplitudes did not differ between IB, RB and IR stimulation protocols, variability was lowest in the IR protocol, compared to IB and RB protocols. Reliability was highest in the IR protocol, compared to IB and IR protocols.

Comparison with existing methods

Randomising TMS intensity between each trial produces less variable and more reliable estimates of corticospinal excitability than previously used blocked protocols and produces the same I/O measures.

Conclusions

Inter-trial randomization of TMS intensities appears to be the most reliable method for constructing I/O curves at multiple time points and decreases the variability of responses.

中文翻译：

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随机刺激强度改善了皮质脊髓兴奋性评估的可变性和可靠性。

背景

经颅磁刺激（TMS）的控制方面的进展已使刺激强度的更大随机化。尚不清楚这种随机化是否能改善对皮质脊髓兴奋性的评估。

新方法

我们在三种TMS方案中记录了11位参与者的第一背骨间背肌的TMS诱发的运动诱发电位（MEP）的幅度：强度增加的块（IB），随​​机块（RB）和刺激间随机化（IR） 。主动运动阈值的90-140％的刺激强度描述了皮质脊髓输入输出（I / O）属性。在五名参与者中重复了该实验。

结果

尽管IB，RB和IR刺激方案之间的MEP幅度没有差异，但与IB和RB方案相比，IR方案中的可变性最低。与IB和IR协议相比，IR协议中的可靠性最高。

与现有方法的比较

与以前使用的封闭方案相比，在每个试验之间使TMS强度随机产生的皮质脊髓兴奋性估计值变化较小且更可靠，并且产生相同的I / O措施。

结论

TMS强度的试验间随机化似乎是在多个时间点构建I / O曲线的最可靠方法，并且降低了响应的可变性。