Is the “end‐of‐study guess” a valid measure of sham blinding during transcranial direct current stimulation?,European Journal of Neuroscience

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Is the “end‐of‐study guess” a valid measure of sham blinding during transcranial direct current stimulation?
European Journal of Neuroscience ( IF 2.7 ) Pub Date : 2020-10-24 , DOI: 10.1111/ejn.15018
Christopher Turner ₁ , Catherine Jackson ₁ , Gemma Learmonth _{1,

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Affiliation

Studies using transcranial direct current stimulation (tDCS) typically incorporate a fade‐in, short‐stimulation, fade‐out sham (placebo) protocol, which is assumed to be indistinct from a 10–30 min active protocol on the scalp. However, many studies report that participants can dissociate active stimulation from sham, even during low‐intensity 1 mA currents. We recently identified differences in the perception of an active (10 min of 1 mA) and a sham (20 s of 1 mA) protocol that lasted for 5 min after the cessation of sham. In the present study we assessed whether delivery of a higher‐intensity 2 mA current would exacerbate these differences. Two protocols were delivered to 32 adults in a double‐blinded, within‐subjects design (active: 10 min of 2 mA, and sham: 20 s of 2 mA), with the anode over the left primary motor cortex and the cathode on the right forehead. Participants were asked “Is the stimulation on?” and “How sure are you?” at 30 s intervals during and after stimulation. The differences between active and sham were more consistent and sustained during 2 mA than during 1 mA. We then quantified how well participants were able to track the presence and absence of stimulation (i.e. their sensitivity) during the experiment using cross‐correlations. Current strength was a good classifier of sensitivity during active tDCS, but exhibited only moderate specificity during sham. The accuracy of the end‐of‐study guess was no better than chance at predicting sensitivity. Our results indicate that the traditional end‐of‐study guess poorly reflects the sensitivity of participants to stimulation, and may not be a valid method of assessing sham blinding.

中文翻译：

“研究终点”是否是经颅直流电刺激过程中假盲致盲的有效措施？

使用经颅直流电刺激（tDCS）进行的研究通常采用渐入，短刺激，渐隐假手术（安慰剂）方案，假定与头皮上的10-30分钟有效方案没有区别。但是，许多研究报告称，即使在1mA低强度电流下，参与者也可以使假刺激脱离主动刺激。我们最近发现了在停止假动作后持续5分钟的主动（10分钟的1 mA）和假（20 s的1 mA）协议的感知上的差异。在本研究中，我们评估了传递更高强度的2 mA电流是否会加剧这些差异。通过双盲，主题内设计向32名成年人提供了两种方案（有效：10分钟2 mA，假时间： 20 s 2 mA），阳极在左主电动机皮质上，阴极在右前额上。参与者被问到“刺激还在吗？” 和“您确定吗？在刺激期间和刺激之后以30 s的间隔间隔。主动和假动作之间的差异在2 mA期间比在1 mA期间更为一致和持续。然后，我们使用交叉相关性量化了参与者在实验过程中追踪刺激的存在与否（即他们的敏感性）的能力。电流强度是活动tDCS期间敏感性的良好分类，但在假手术期间仅表现出中等特异性。研究结束猜测的准确性没有比预测灵敏度更好的机会了。我们的结果表明，传统的研究结局猜测不能很好地反映参与者对刺激的敏感性，并且可能不是评估假盲的有效方法。

更新日期：2020-10-24

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