PONE-D-21-37330Transcutaneous spinal direct current stimulation (tsDCS) does not affect postural sway during quiet upright standingPLOS ONE

Dear Dr. Fava de Lima,

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Support of the State of S˜ao Paulo (FAPESP 2016/10614-4) and by the Brazilian 369

Council of Science and Technology (CNPq, 303809/2016-7)."

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The paper by de Lima and co-workers reports interesting findings about the possibility to modulate postural sway by using spinal tDCS. The methods are sound and the paper requires only minor revisions:

- The Introduction needs a language editing;

- Did Authors use a questionnaire to assess possible side-effects of tsDCS?

- Though do not statistically significant, the results may depend on the montage used and probably differ between health and disease. The uthors should discuss both these critical points in detail.

- Which are the putative supraspinal pathways modulated by this particular montage?

Reviewer #2: The authors present their findings related to the change in static balance performance in conjunction with transcutaneous direct current spinal stimulation. This investigation was performed in a young healthy sample and while there report negative findings the authors have proposed a novel sham method. One factor that reduces my enthusiasm for the manuscript is that the authors do not report how they determined their sham was as and/or more effective than traditional tsDCS methods. Adding this information would increase the beneficial information disseminated and help other investigators perform more rigorous future tsDCS studies. To strengthen the manuscript's importance to the greater body of research the authors should also better justify their sample selection. Typically the young healthy population performs well on tests of static balance, making this population a less than ideal population to sample from. However, because there are not many tsDCS studies one could better justify this sample by including tests of safety, tolerability, etc. Another point that could be better justified is the eyes closed methodology. This was likely done to increase the difficulty of the balance test in turn leading to a greater probability of detecting an effect.

In general, I believe the manuscript possesses merit for publication but believe it can be significantly strengthened by addressing the above comments. A list of specific comments is presented below.

Title and Abstract: I suggest characterizing the sample as young and healthy in the title and abstract. Readers will likely acknowledge that the lack of tsDCS effect is because of the sample and not because the technology doesn’t work.

Introduction:

Line 70: Your null hypothesis is misstated

Methods:

L117: Report the range of stimulation/current densities in the literature with references. This will allow readers to understand where/how your protocol fits into what has previously been done.

Report the balance of the groups. With a small sample, randomization may lead to an imbalance in the order of the performed simulations. Is there an order effect because more sham procedures were done before actual stimulation trials?

Better describe why some data was excluded. The figure provided shows an example of excluded data but explain to the reader why that pattern is abnormal. Provide references to justify if possible.

Better describe the identification of T10, I assume it was through palpation? Was it supervised by physical therapists or other clinicians? If the research staff is properly trained or has experience please cite a reference.

Results:

L214: Report Ht and Wt. BMI reflects health status and is not relevant to this investigation.

L225: Null hypothesis doesn’t match the intro, ensure consistency (intro null hypothesis is not correct)

L230: Indicate where in the figure this significant finding is. Added letters or numbers to each panel of the figure to allow more clear references between the text and figure.

Report if your novel blinding technique worked. How many participants were able to correctly identify if they received active or sham stimulation.

Report all minor and major adverse events. This will help establish the safety of the technique and add importance to your negative findings.

Discussion:

Line 241-252: It is unclear why AC is mentioned. There is no information about AC in the intro. The discussion would be more clear if you restated your hypotheses and findings.

L320: No data presented to support your blinding method

L342: You present no effect sized in your results and you did not say you calculated them in your methods. Either remove from your discussion or add the information to the previous sections. If you discuss data from the study it should be reported in the appropriate sections. (it can be supplementary data if you so choose)

You report several significant interactions but there is no mention of them in your discussion. You cannot ignore findings that you report even if they may not have much clinical relevance. Discuss why/what those findings may or may not signify

Discuss how much of an effect you might have found in young healthy individuals. Cite previous works showing young healthy balance can be improved and why this was the proper population to test your hypotheses.

Figure 3: Added identifiers to each panel for easy reference from the test. You state significant results but did not indicate them in the figure or figure legend (F50p_PSD…)

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Reviewer #1: Yes: Tommaso Bocci

Reviewer #2: Yes: John H. Kindred

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Transcutaneous spinal direct current stimulation (tsDCS) does not affect postural sway of young and healthy subjects during quiet upright standing

PONE-D-21-37330R1

Dear Dr. Fava de Lima,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

François Tremblay, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Please make sure that the manuscript is properly edited for grammatical and typographical errors when preparing the final version.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: I thank the authors for putting in the work to improve their submission. The authors have addressed all of my concerns and I look forward to seeing more of their work in the future.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: Yes: John H. Kindred, Ph.D.