The Time Course of Ineffective Sham Blinding During 1mA tDCS

Greinacher, Robert; Buhôt, Larissa; Möller, Lisa; Learmonth, Gemma

doi:10.1101/462424

Cited by 5 publications

(21 citation statements)

References 35 publications

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“…One important difference is the duration of the real tDCS: Whereas in our study it was 20 min, Greinacher et al. () used 10 min. Blinding efficacy of FSF protocols seems to be better for real tDCS protocols with shorter stimulation durations (e.g., 10 min).…”

Section: Discussionmentioning

confidence: 77%

“…The stimulation parameters used in this study were similar to the ones reported here: Both used 1 mA tDCS, comparable electrode montage and a FSF protocol (with identical fade-in/out periods and similar shortstimulation periods: 15 vs. 20 s). One important difference is the duration of the real tDCS: Whereas in our study it was 20 min, Greinacher et al (2018) used 10 min. Blinding efficacy of FSF protocols seems to be better for real tDCS protocols with shorter stimulation durations (e.g., 10 min).…”

Section: Discussionmentioning

confidence: 87%

“…FSF protocols in this stimulation parameter range were previously assumed to be effective for maintaining blinding (Ambrus et al., ). Contrary to the expectations, participants were able to correctly identify active sham and real tDCS protocols based on the differences in the time‐course of the subjectively perceived cutaneous discomfort (Greinacher et al., ). The stimulation parameters used in this study were similar to the ones reported here: Both used 1 mA tDCS, comparable electrode montage and a FSF protocol (with identical fade‐in/out periods and similar short‐stimulation periods: 15 vs. 20 s).…”

Section: Discussionmentioning

confidence: 94%

“…In a recent pre‐registered study it was shown that the blinding efficacy of the FSF protocol is compromised even for the most frequently used 1 mA and 10 minute‐long real tDCS protocol, when a repeated‐measure study design is used (Greinacher et al., ). In this study, tDCS was applied over the left primary motor cortex (anode) and over the right supraorbital region (cathode).…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, the results of this study may have overestimated the degree to which subjects are able to distinguish sham from real stimulation in most common study setups that do not feature repeated evaluations. In our study, participants performed a cognitive task while receiving the stimulation and they were only asked about blinding retrospectively (as, indeed, subjects in Greinacher et al., , also were). This assessment method is the most common way in studies aiming to measure the possible cognitive effects of tDCS.…”

Section: Discussionmentioning

confidence: 99%

See 4 more Smart Citations

Blinding is compromised for transcranial direct current stimulation at 1 mA for 20 min in young healthy adults

Turi

Csifcsák

Boayue

et al. 2019

Eur J of Neuroscience

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Transcranial direct current stimulation (tDCS) is a non‐invasive brain stimulation method that is frequently used to study cortical excitability changes and their impact on cognitive functions in humans. While most stimulators are capable of operating in double‐blind mode, the amount of discomfort experienced during tDCS may break blinding. Therefore, specifically designed sham stimulation protocols are being used. The “fade‐in, short‐stimulation, fade‐out” (FSF) protocol has been used in hundreds of studies and is commonly believed to be indistinguishable from real stimulation applied at 1 mA for 20 min. We analysed subjective reports of 192 volunteers, who either received real tDCS (n = 96) or FSF tDCS (n = 96). Participants reported more discomfort for real tDCS and correctly guessed the condition above chance‐level. These findings indicate that FSF does not ensure complete blinding and that better active sham protocols are needed.

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Section: Discussionmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 87%

Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 3 more Smart Citations

Blinding is compromised for transcranial direct current stimulation at 1 mA for 20 min in young healthy adults

Turi

Csifcsák

Boayue

et al. 2019

Eur J of Neuroscience

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show abstract

Investigating the Effects of tDCS on Visual Orientation Discrimination Task Performance: “the Possible Influence of Placebo”

et al. 2019

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The non-invasive neuromodulation technique tDCS offers the promise of a low-cost tool for both research and clinical applications in psychology, psychiatry, and neuroscience. However, findings regarding its efficacy are often equivocal. A key issue is that the clinical and cognitive applications studied are often complex and thus effects of tDCS are difficult to predict given its known effects on the basic underlying neurophysiology, namely alterations in cortical inhibition-excitation balance. As such, it may be beneficial to assess the effects of tDCS in tasks whose performance has a clear link to cortical inhibition-excitation balance such as the visual orientation discrimination task (ODT). In prior studies in our laboratory, no practice effects were found during 2 consecutive runs of the ODT, thus in the current investigation, to examine the effects of tDCS, subjects received 10 min of 2 mA occipital tDCS (sham, anode, cathode) between a first and second run of ODT. Surprisingly, subjects' performance significantly improved in the second run of ODT compared to the first one regardless of the tDCS stimulation type they received (anodal, cathodal, or sham-tDCS). Possible causes for such an improvement could have been due to either a generic "placebo" effect of tDCS (as all subjects received some form of tDCS) or an increased delay period between the two runs of ODT of the current study compared to our previous work (10-min duration required to administer tDCS as opposed to~2 min in previous studies as a "break"). As such, we tested these two possibilities with a subsequent experiment in which subjects received 2-min or 10-min delay between the 2 runs (with no tDCS) or 10 min of sham-tDCS. Only sham-tDCS resulted in improved performance thus these data add to a growing literature suggesting that tDCS has powerful placebo effect that may occur even in the absence of active cortical modulation.

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Role of skin tissue layers and ultra-structure in transcutaneous electrical stimulation including tDCS

Khadka

Bikson²

2020

Phys. Med. Biol.

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Background. During transcranial electrical stimulation (tES), including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), current density concentration around the electrode edges that is predicted by simplistic skin models does not match experimental observations of erythema, heating, or other adverse events. We hypothesized that enhancing models to include skin anatomical details, would alter predicted current patterns to align with experimental observations. Method. We develop a high-resolution multi-layer skin model (epidermis, dermis, and fat), with or without additional ultra-structures (hair follicles, sweat glands, and blood vessels). Current flow patterns across each layer and within ultra-structures were predicted using finite element methods considering a broad range of modeled tissue parameters including 78 combinations of skin layer conductivities (S m–1): epidermis (standard: 1.05 × 10−5; range: 1.05 × 10−6 to 0.465); dermis (standard: 0.23; range: 0.0023 to 23), fat (standard: 2 × 10−4; range: 0.02 to 2 × 10−5). The impact of each ultra-structures in isolation and combination was evaluated with varied basic geometries. An integrated final model is then developed. Results. Consistent with prior models, current flow through homogenous skin was annular (concentrated at the electrode edges). In multi-layer skin, reducing epidermis conductivity and/or increasing dermis conductivity decreased current near electrode edges, however no realistic tissue layer parameters produced non-annular current flow at both epidermis and dermis. Addition of just hair follicles, sweat glands, or blood vessels resulted in current peaks around each ultrastructure, irrespective of proximity to electrode edges. Addition of only sweat glands was the most effective approach in reducing overall current concentration near electrode edges. Representation of blood vessels resulted in a uniform current flow across the vascular network. Finally, we ran the first realistic model of current flow across the skin. Conclusion. We confirm prior models exhibiting current concentration near hair follicles or sweat glands, but also exhibit that an overall annular pattern of current flow remains for realistic tissue parameters. We model skin blood vessels for the first time and show that this robustly distributes current across the vascular network, consistent with experimental erythema patterns. Only a state-of-the-art precise model of skin current flow predicts lack of current concentration near electrode edges across all skin layers.

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The Time Course of Ineffective Sham Blinding During 1mA tDCS

Cited by 5 publications

References 35 publications

Blinding is compromised for transcranial direct current stimulation at 1 mA for 20 min in young healthy adults

Blinding is compromised for transcranial direct current stimulation at 1 mA for 20 min in young healthy adults

Investigating the Effects of tDCS on Visual Orientation Discrimination Task Performance: “the Possible Influence of Placebo”

Role of skin tissue layers and ultra-structure in transcutaneous electrical stimulation including tDCS

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