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

Turner, Christopher W.; Jackson, Catherine; Learmonth, Gemma

doi:10.1111/ejn.15018

Cited by 26 publications

(24 citation statements)

References 37 publications

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“…The sham stimulation consisted of a 1 s fade in followed by a 1 s fade out at a fixed frequency. This application of a current every 8 s in all three conditions should ensure a better blinding than established methods of only comparatively very short placebo-conditions, which have been recently criticized ( Turner et al, 2021 ).…”

Section: Methodsmentioning

confidence: 99%

A Comparison of Closed Loop vs. Fixed Frequency tACS on Modulating Brain Oscillations and Visual Detection

Stecher

Notbohm²,

Kasten

et al. 2021

Front. Hum. Neurosci.

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Transcranial alternating current stimulation has emerged as an effective tool for the exploration of brain oscillations. By applying a weak alternating current between electrodes placed on the scalp matched to the endogenous frequency, tACS enables the specific modulation of targeted brain oscillations This results in alterations in cognitive functions or persistent physiological changes. Most studies that utilize tACS determine a fixed stimulation frequency prior to the stimulation that is kept constant throughout the experiment. Yet it is known that brain rhythms can encounter shifts in their endogenous frequency. This could potentially move the ongoing brain oscillations into a frequency region where it is no longer affected by the stimulation, thereby decreasing or negating the effect of tACS. Such an effect of a mismatch between stimulation frequency and endogenous frequency on the outcome of stimulation has been shown before for the parietal alpha-activity. In this study, we employed an intermittent closed loop stimulation protocol, where the stimulation is divided into short epochs, between which an EEG is recorded and rapidly analyzed to determine a new stimulation frequency for the next stimulation epoch. This stimulation protocol was tested in a three-group study against a classical fixed stimulation protocol and a sham-treatment. We targeted the parietal alpha rhythm and hypothesized that this setup will ensure a constant close match between the frequencies of tACS and alpha activity. This closer match should lead to an increased modulation of detection of visual luminance changes depending on the phase of the tACS and an increased rise in alpha peak power post stimulation when compared to a protocol with fixed pre-determined stimulation frequency. Contrary to our hypothesis, our results show that only a fixed stimulation protocol leads to a persistent increase in post-stimulation alpha power as compared to sham. Furthermore, in none of the stimulated groups significant modulation of detection performance occurred. While the lack of behavioral effects is inconclusive due to the short selection of different phase bins and trials, the physiological results suggest that a constant stimulation with a fixed frequency is actually beneficial, when the goal is to produce persistent synaptic changes.

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Section: Methodsmentioning

confidence: 99%

A Comparison of Closed Loop vs. Fixed Frequency tACS on Modulating Brain Oscillations and Visual Detection

Stecher

Notbohm²,

Kasten

et al. 2021

Front. Hum. Neurosci.

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“…Another limitation of this study is that the blinding protocol may not have been successful, which is common in tDCS research, especially when higher intensities (≥2 mA) are used [51][52][53]. Therefore, more research is needed on ways to improve blinding protocols, such as the use of topical anesthetic creams (e.g., EMLA cream) [54,55] and/or assessing blinding during the stimulation rather than the common end-of-study guess [56]. Lastly, we did not assess environmental changes, psychological stress, or how the participants perceived PPE was affecting their performance (e.g., more difficult breathing), which may have influenced the subjects' fatigue profiles.…”

Section: Discussionmentioning

confidence: 99%

Personal Protective Equipment Alters Leg Muscle Fatigability Independent of Transcranial Direct Current Stimulation: A Comparison with Pre-COVID-19 Pandemic Results

et al. 2021

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In response to the COVID-19 pandemic, the use of personal protective equipment (PPE; e.g., face mask) has increased. Mandating subjects to wear PPE during vigorous exercise might affect the fatigue outcomes of transcranial direct current stimulation (tDCS) studies. The purpose of this study was to investigate whether the use of PPE affected the performance of a tDCS-influenced fatigue task in healthy adults. A total of 16 young and healthy subjects were recruited and wore PPE during an isokinetic fatigue task in conjunction with sham, 2 mA, and 4 mA tDCS conditions. Subjects were matched to subjects who did not wear PPE during our previous pre-pandemic study in which right knee extensor fatigability increased under these same conditions. The results show that right knee extensor fatigability, derived from torque and work (FI-T and FI-W, respectively), was higher in the PPE study compared to the No PPE study in the sham condition. Additionally, there were no differences in knee extensor fatigability or muscle activity between sham, 2 mA, and 4 mA tDCS in the present study, which contrasts with our previous results. Thus, PPE worn by subjects and researchers might have a detrimental effect on fatigue outcomes in tDCS studies irrespective of the stimulation intervention.

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“…Some authors advocate for a more comprehensive blinding evaluation which would include asking the participants if they think the stimulation is on while receiving it and to estimate how confident they are in their answer [ 28 , 32 , 34 , 61 ]. However, this may cause participants to overly focus on side-effects throughout the session, which can itself compromise blinding as well as the outcome measures of interest.…”

Section: Discussionmentioning

confidence: 99%

“…To estimate whether blinding was successful, researchers typically adopt the end-of-study guess approach, when participants in both active and control groups are asked to guess if they have received the active or sham stimulation after the session [ 34 ] or, in crossover designs, to try to guess in which session they have received the sham stimulation [ 44 ]. Utilization of the end-of-study guess to assess the successfulness of blinding is a frequent approach in tDCS studies [ 28 , 32 , 33 , 45 , 46 , 47 ].…”

Section: Methodsmentioning

confidence: 99%

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Blinding in tDCS Studies: Correct End-of-Study Guess Does Not Moderate the Effects on Associative and Working Memory

et al. 2021

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Transcranial direct current stimulation (tDCS) has become a valuable tool in cognitive neuroscience research as it enables causal inferences about neural underpinnings of cognition. However, studies using tDCS to modulate cognitive functions often yield inconsistent findings. Hence, there is an increasing interest in factors that may moderate the effects, one of which is the participants’ beliefs of the tDCS condition (i.e., real or sham) they received. Namely, whether participants’ correct guessing of sham condition may lead to false-positive tDCS effects. In this study, we aimed to explore if participants’ beliefs about received stimulation type (i.e., the success of blinding) impacted their task performance in tDCS experiments on associative (AM) and working memory (WM). We analyzed data from four within-subject, sham-controlled tDCS memory experiments (N = 83) to check if the correct end-of-study guess of sham condition moderated tDCS effects. We found no evidence that sham guessing moderated post-tDCS memory performance in experiments in which tDCS effects were observed as well as in experiments that showed null effects of tDCS. The results suggest that the correct sham guessing (i.e., placebo-like effect) is unlikely to influence the results in tDCS memory experiments. We discuss the results in light of the growing debate about the relevance and effectiveness of blinding in brain stimulation research.

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

Cited by 26 publications

References 37 publications

A Comparison of Closed Loop vs. Fixed Frequency tACS on Modulating Brain Oscillations and Visual Detection

A Comparison of Closed Loop vs. Fixed Frequency tACS on Modulating Brain Oscillations and Visual Detection

Personal Protective Equipment Alters Leg Muscle Fatigability Independent of Transcranial Direct Current Stimulation: A Comparison with Pre-COVID-19 Pandemic Results

Blinding in tDCS Studies: Correct End-of-Study Guess Does Not Moderate the Effects on Associative and Working Memory

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