Exploring neural entrainment and synchrony in response to repeated 60 Hz flickering white light in healthy volunteers

MohammadAmin Alamalhoda; Friederike Leesch; Francesca Giovanetti; Eoghan Dunne; Giuseppina Pilloni; Mark Caffrey; Jack O’Keeffe; Alessandro Venturino; Maria Teresa Ferretti

doi:10.1371/journal.pone.0332310

Peer Review History

Original SubmissionFebruary 26, 2025
15 May 2025 Decision Letter - Gennady Cymbalyuk, Editor PONE-D-25-10411Flickering white light stimulation at 60 Hz induces strong, widespread neural entrainment and synchrony in healthy subjectsPLOS ONE Dear Dr. ferretti, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Reviewers agree the topic is interesting but identify several critical shortcomings that preclude acceptance in its current form. First, the choice of sixty hertz is weakly justified because the established forty hertz control is absent and supporting citations are missing. Second, the sample size of six completers per arm is too small to sustain claims about adaptation or safety, so the authors must recruit more participants or temper their conclusions. Third, the methods are not described in enough detail; information on light-intensity calibration, full EEG preprocessing, questionnaire content, and statistical decision rules is required to rule out confounds such as day-to-day intensity drift. These gaps undermine the reported decline in entrainment because adaptation is not tracked daily, across weekends, or after the treatment ends. Electrode-level differences remain qualitative, and demographic balance after dropouts is unclear. Addressing these points is essential before the work can be considered further.. Please submit your revised manuscript by Jun 29 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . 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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: No Reviewer #2: Partly ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: No ****** 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 ****** 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 ****** 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: Major comments: 1. The choice of 60 Hz for stimulation requires clearer justification. Given the growing body of evidence supporting 40 Hz entrainment in modulation neural activity, a comparison between 40 Hz and 60 Hz stimulation would provide a more informative perspective. The rationale for selecting 60 Hz should be explicitly discussed, particularly in relation to known effects. 2. The final sample size (n = 6 per group after dropouts) is small, particularly for EEG-based study on younger adults. Furthermore, the observed subject variability in entrainment strength across the 3 EEG sessions makes drawing any strong conclusions about the habituation effect difficult. 3. It is unclear whether light intensity was adjusted on each day and how this was accounted for in the analyses. If intensity varied across days or between participants, this could have confounded the results. As stimulus intensity can influence the response, it is important to confirm that the total stimulus power was comparable between sessions and conditions. Without this control, it is difficult to determine whether reduced entrainment strength is due to habituation or changes in stimulus intensity. 4. The Methods section lacks a description of EEG preprocessing and analysis steps, which are critical for interpreting the EEG findings. Additionally, the questionnaires used for assessing tolerability and other outcomes are not described. These methodological omissions should be addressed to ensure reproducibility and transparency. 5. The manuscript would benefit from additional analysis of the temporal dynamics of the observed effects (comparing pre-, during, and post-stimulation). This would provide additional insight into whether such stimulation has transient or longer-lasting effects. 6. Demographic comparisons appear to have been conducted on the full sample, but two participants in the Active group were excluded from EEG and biomarker analysis. It would be helpful to clarify whether the demographic balance remained after these dropouts, especially since the final analysis excluded their data. 7. The authors mention that statistical test selection was based on the outcome of normality tests. However, repeated measures were analyzed with two-way ANOVA, which assumes normality. It should be clarified whether ANOVA was applied only to variables that passed normality checks, or if a non-parametric alternative was considered when assumptions were violated. 8. The Discussion references “quality-of-life” assessments, but these are not clearly defined or discussed elsewhere in the manuscript. It is important to distinguish between assessing tolerability/safety and evaluating quality of life, as these represent different outcomes. Minor comments: 1. Several sentences should be revised. E.g., “Additional infos on light stimulation device and the mini-Faraday cage in Supplementary Methods”, “Additional infos and EEG data analysis in Supplementary Methods”. 2. Some sections include excessive technical detail (e.g. manufacturer part numbers, catalog numbers) that could be moved to the Supplementary Materials to improve readability and flow. Reviewer #2: The authors investigated the effect of 20-minute, 60 Hz light flickering stimulation applied on a daily basis for the first 5 days during 3 consecutive weeks on EEG activity measured with an 8-channel system in 8(6) healthy young volunteers versus 6 controls. They also collected saliva samples to evaluate CRP and cortisol levels immediately after light stimulation, which were not elevated in either of the two groups. There was no task or behavioural assessment involved, other than general questions about well-being, which did not show any systematic difference between the active and the sham groups. Participants receiving flicker stimulation presented 60 Hz entrainment on all 8 electrodes, as revealed by power spectral density measures and overall synchrony between the signals for all electrodes studied using pairwise phase-locking values. By the 5th day of light treatment, there was a significant decline in the 60 Hz-related power on the electrodes, and an apparently even stronger decline by the 19th day. The authors conclude that this decline may reflect adaptation and/or plasticity, that the protocol has no harmful effects and that it might thus be suitable for clinical treatment. General comments 1. The choice of 60 Hz is not sufficiently justified. One of the reasons the authors cite is that this frequency was not explored in humans before, but they fail to cite other studies using 60 Hz sensory stimulation who also compare effects of other frequencies (e.g., Manippa et al., 2024) and their effects on task performance. This set of studies suggested a positive effect of 60 Hz auditory stimulation on executive functions such as cognitive control and attention (not memory). 2. At least one lower frequency should have been tested as a control. In the cited animal study (Venturino et al., 2021), 60 Hz—compared to 40 Hz—had a specific effect on PNN/microglia, which could have been directly contrasted. 3. The number of participants who completed the EEG study is too low, with only 6 in the active group. Since the protcol is not harmful, this low number might be reconsidered. Maybe, because of that, the data also seem under-analysed with regard to effects within individuals over time, and analysis of differences between electrodes. Given that there are reports that gamma stimulation does not even reach the hippocampus that point might be important to adress. 4. The protocol does not appear fully consistent. What was the reason for not stimulating on weekends? One would expect daily stimulation to observe adaptation dynamics more precisely. 5. EEG recordings should have been conducted on consecutive days during at least one week to investigate the timeline of entrainment decline. For example, was there any recovery over the weekend, or was the decline sharper during consecutive days? 6. It remains unclear how long the adaptation effect lasted after the flicker stimulation ended. One could have included a follow-up. 7. There are references missing on the impact of sensory gamma stimulation on the glymphatic system. Detailed comments 1. Figure 1G: which electrode is shown? Please show at least two different ones. 2. Although the overall analysis suggests entrainment and adaptation across all electrodes, there seem to be considerable differences between them as suggested by the images. These differences should be quantified (for example, in Figure 2A, active group day 1). 3. A comment should be made on why the frontal or temporal electrodes seem to adapt more than the occipital ones, which are closer to the flickering visual input. 4. A discussion and citations should be included on which stimulation frequencies are able to induce entrainment in the visual system. 5. How much decline in 60 Hz entrainment occurred during a single 20-minute session after 5 and 19 days? ****** 6. 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 #1: No Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0332310.r001
Revision 1
14 Jul 2025 Author Response Reviewer #1 Major comments: 1. The choice of 60 Hz for stimulation requires clearer justification. Given the growing body of evidence supporting 40 Hz entrainment in modulation neural activity, a comparison between 40 Hz and 60 Hz stimulation would provide a more informative perspective. The rationale for selecting 60 Hz should be explicitly discussed, particularly in relation to known effects. We thank the Reviewer for this important comment. In the revised introduction, we clarified and expanded the rationale for selecting 60 Hz stimulation and included relevant citations demonstrating its emerging significance. Specifically, we now reference recent studies using 60 Hz transcranial alternating current stimulation (tACS) and auditory stimulation in humans, including those by: Manippa et al. (2024), who reported reduced intrusion errors and enhanced cognitive control in healthy adults following 60 Hz auditory stimulation, Nomura et al. (2019), who demonstrated that 60 Hz tACS over the dorsolateral prefrontal cortex (DLPFC) enhances declarative long-term memory (LTM). These additions provide context regarding the functional relevance of 60 Hz gamma-band activity in executive and memory-related processes and address the concern that the original text lacked supporting human data. Further, we emphasize that while 60 Hz has been tested in auditory and electrical protocols, its use in visual entrainment, especially over multiple weeks, remains largely unaddressed. Our study aims to explore this area. This point has been explicitly stated in the revised introduction (page 5 lines 97-105). We agree that a lot is known on the effects of 40 Hz and a direct comparison with 60 Hz would be interesting to perform. Our goal for the present study was to generate a knowledge base with a full characterization of 60 Hz light stimulation over time – something that is missing in the literature. As a subsequent study, a direct comparison with 40 Hz would be highly relevant. To acknowledge this, in the Limitations section, we added a paragraph acknowledging the limitations of our study, such as the absence of 40 Hz for direct comparison of effects, as well as the broader absence of comparable human data on the effects of different frequency visual stimulation. By clearly outlining these gaps and open questions, we hope to facilitate future research on frequency-specific neuromodulation. 2. The final sample size (n = 6 per group after dropouts) is small, particularly for EEG-based study on younger adults. Furthermore, the observed subject variability in entrainment strength across the 3 EEG sessions makes drawing any strong conclusions about the habituation effect difficult. We acknowledge the Reviewer's concerns about the small sample size and its implications for statistical power. Our study was designed (and approved by the Ethics Commission of Lower Austria) to be an initial, pilot investigation to evaluate the feasibility, safety and neurological effects of 60 Hz flickering light stimulation over an extended period, which was never done before in the literature. Such a small sample size has been previously used in some EEG studies, such as Sharpe et al., 2020 and Mangia et al., PLOS ONE 2014 (now quoted). We also agree with the Reviewer on the high variability in entrainment strength, which limits our ability to make strong conclusions about habituation. In response, we have revised the manuscript to temper these claims, emphasising the exploratory nature of our findings and the necessity for larger-scale studies to validate and extend our results. These clarifications have been incorporated into the abstract (page 2, line 40-43 and 48-49) and discussion section (pages 31- 35, sections 4.2 to 4.5, and especially 4.6 limitations pages 36-37). We have also modified the title accordingly, which now reads ´Exploring Neural Entrainment and Synchrony in Response to Repeated 60 Hz Flickering White Light in Healthy Volunteers´. 3. It is unclear whether light intensity was adjusted on each day and how this was accounted for in the analyses. If intensity varied across days or between participants, this could have confounded the results. As stimulus intensity can influence the response, it is important to confirm that the total stimulus power was comparable between sessions and conditions. Without this control, it is difficult to determine whether reduced entrainment strength is due to habituation or changes in stimulus intensity. We thank the Reviewer for this valuable feedback, indeed this is an important point to clarify. The stimulation protocol was designed to ensure safety and comfort, allowing for individualised light intensity settings (within a given range) based on verbal feedback from participants. To assess whether the intensity chosen could influence the entrainment and habituation observed, we have now performed an additional analysis to explore the changes in intensity levels selected by participants across the days. This analysis (presented in SI 1Fig D-E) revealed that participants chose an average light intensity of approximately 80 μW (SD: 7 μW). Notably, intra-individual variation over the 15 stimulation days was minimal, with a maximum SD of 9 μW for any single participant, representing less than 11% of the mean intensity. No decline in light intensity was observed over the days of stimulation, suggesting that this is not a factor involved in the observed habituation. Given this consistency across subjects and days, and the absence of a reduction in intensity over time, we believe it is unlikely that small day-to-day variations in stimulus power explain the observed reduction in entrainment strength over time. This important point has now been clarified in both the Methods and Discussion sections. 4. The Methods section lacks a description of EEG preprocessing and analysis steps, which are critical for interpreting the EEG findings. Additionally, the questionnaires used for assessing tolerability and other outcomes are not described. These methodological omissions should be addressed to ensure reproducibility and transparency. We thank the Reviewer for this valuable observations regarding the Materials and Methods section, giving us an opportunity to improve its readability and transparency. We agree that the choice to place some of the key information in Supplementary might not have been ideal, so we have significantly restructured the M&M section accordingly. First, we have incorporated the supplementary materials and methods section into the main text – this includes thorough details on EEG preprocessing (Page 11 lines 248-260) and tolerability and blinding questionnaires (page 16, lines 353-367). In addition, to increase readability, in the revised manuscript, we have thoroughly restructured several paragraphs, including the Signal Processing and Analysis section, and added clearly labeled subheadings for each step of the EEG pipeline: “EEG Preprocessing,” “FFT Analysis,” “Topoplots,” “STFT,” and “PLV Calculation.”. Also, addressing Minor Comment 2 below, we have moved the technical details (manufacturer´s names and catalogue numbers of device components) to a separate table (SI Table 2), to improve the flow. 5. The manuscript would benefit from additional analysis of the temporal dynamics of the observed effects (comparing pre-, during, and post-stimulation). This would provide additional insight into whether such stimulation has transient or longer-lasting effects. We thank the Reviewer for this suggestion regarding a further exploration of our data to assess the temporal dynamics of neural entrainment. Each EEG session included three consecutive recording phases: a five-minute baseline period (no light), a five-minute period of constant light exposure, and a 20-minute stimulation phase (60-Hz flickering light or constant light). This design enabled us to compare neural activity pre-stimulation and during stimulation within each session. Following the Reviewer’s comment, we have performed an additional temporal analysis to characterize the dynamics of entrainment during stimulation with more granularity. Specifically, we have divided the 20 min stimulation period into five non-overlapping, 4 minute intervals and analyzed the normalized 60-Hz power within each segment. The results showed that entrainment strength remained stable throughout the 20-minute stimulation phase, across all three days (Day 1, Day 5, and Day 19). This suggests sustained entrainment, with no evidence of decay or rapid adaptation during the stimulation period. This new analysis is included as SI Fig 3. However, we acknowledge that our protocol did not include EEG recordings after the stimulation phase. Consequently, we cannot directly assess post-stimulation effects or the potential persistence of entrainment. We now explicitly state this limitation in the Results section (page 33, lines 755-758). The Results paragraph now reads: Our experimental design allowed us to study in detail the changes in entrainment power comparing pre-stimulation and during stimulation conditions. We must note that post-stimulation effects or the potential persistence of entrainment were not explored in this experiment and would be the subject of subsequent studies. 6. Demographic comparisons appear to have been conducted on the full sample, but two participants in the Active group were excluded from EEG and biomarker analysis. It would be helpful to clarify whether the demographic balance remained after these dropouts, especially since the final analysis excluded their data. We thank the Reviewer for highlighting this important aspect. Although initially conducted on the full randomized sample (N = 14), we agree that it is important to assess demographic balance within the final analysis cohort (N = 12), which comprises only participants with complete EEG and biomarker data. A re-analysis of the data was therefore performed. As a result we found that the 2 drop outs did not substantially affect the group balance, since there were no statistically significant differences between the groups in the final analysis sample in terms of age, sex, race or years of education. Updated group statistics and comparisons are included now in Table 1 for transparency and a clarification has been added in the accompanying text and caption (page 18) as follows: Two participants in the active group discontinued the study for personal reasons. Because of incomplete data, their EEG and biochemical measurements were excluded from the data analysis. However, both individuals completed the final questionnaire, and their responses on subjective tolerability, blinding and side effects were included in the relevant analyses. The groups remained balanced also after the two dropouts (Table 1). 7. The authors mention that statistical test selection was based on the outcome of normality tests. However, repeated measures were analyzed with two-way ANOVA, which assumes normality. It should be clarified whether ANOVA was applied only to variables that passed normality checks, or if a non-parametric alternative was considered when assumptions were violated. We thank the Reviewer for pointing this to us. We are sorry that our text in the Statistic section was not clear in this regard. Indeed all data have been tested for normality and parametric tests have been used only when the normality was ensured. We have now edited the section (page 17) to clarify this, as follows: ´Statistical analysis for biomarker, demographic and questionnaire data were performed using GraphPad (versions 5 and 10.4) The Shapiro-Wilk test was used to assess the normality of the data. Age and years of education did not show a normal distribution and were analyzed with a Wilcoxon rank-sum test. Cortisol levels followed a normal distribution and were analyzed using a two-way ANOVA to evaluate the interaction between group (active versus sham) and time. Since CRP levels did not meet the normality assumption, they were analyzed using the Kruskal–Wallis test. Ordinal questionnaire responses were evaluated using the Wilcoxon rank-sum test. Proportions (race, sex and blinding efficacy) were compared using Fisher's exact test. A significance threshold of p < 0.05 was applied to all tests.´ 8. The Discussion references “quality-of-life” assessments, but these are not clearly defined or discussed elsewhere in the manuscript. It is important to distinguish between assessing tolerability/safety and evaluating quality of life, as these represent different outcomes. We thank the Reviewer for highlighting this distinction. We acknowledge that the term 'quality of life' was used inaccurately in the Discussion, as we did not administer any standardised instruments that would enable us to assess quality of life. In our study, we collected subjective reports related to tolerability and perceived well-being, including minor side effects, willingness to continue stimulation and overall participant impressions. To address this, we have revised the relevant sentence in the Discussion section to reflect the scope of the data collected. The term 'quality of life' has been replaced with a more appropriate description of tolerability and subjective experience (page 35). Reviewer 1 Minor comments: 1. Several sentences should be revised. E.g., “Additional infos on light stimulation device and the mini-Faraday cage in Supplementary Methods”, “Additional infos and EEG data analysis in Supplementary Methods”. Thanks for this comment. We have revised the text to reflect the fact that the additional methods are now in the main manuscript text, and edited those sentences accordingly. 2. Some sections include excessive technical detail (e.g. manufacturer part numbers, catalog numbers) that could be moved to the Supplementary Materials to improve readability and flow. We concur with the Reviewer and have moved the technical details (manufacture´s names and catalogue numbers for device components) to a separate Supplementary table (SI Table 2), to improve the flow and readability. Reviewer #2 General comments 1. The choice of 60 Hz is not sufficiently justified. One of the reasons the authors cite is that this frequency was not explored in humans before, but they fail to cite other studies using 60 Hz sensory stimulation who also compare effects of other frequencies (e.g., Manippa et al., 2024) and their effects on task performance. This set of studies suggested a positive effect of 60 Hz auditory stimulation on executive functions such as cognitive control and attention (not memory). Thanks for this important comment. We acknowledge that the rationale for chosing 60 Hz might have not been sufficiently explained in the original version of the manuscript. In the revised introduction, we now clarify and expand the rationale for selecting 60 Hz. We emphasize that while 60 Hz has been tested in auditory and electrical protocols, its use in visual entrainment, especially over multiple weeks, remains largely unaddressed. Our study aims to explore this area. This point has been explicitly stated in the revised introduction (page 5 lines 97-105). We also thank the Reviewer for pointing us to key references in this field. These are very useful to provide context to our findings and support an interesting role of 60 Hz modulation in humans. Accordingly, we now reference: Manippa et al. (2024), who reported reduced intrusion errors and enhanced cognitive control in healthy adults following 60 Hz auditory stimulation, Nomura et al. (2019) who demonstrated that 60 Hz tACS over the dorsolateral prefrontal cortex (DLPFC) enhances declarative long-term memory (LTM). We still note that much less literature exists on 60 Hz entrainment (especially driven by flickering light) as compared to 40 Hz, which has been extensively studied. Given its functional relevance in executive and memory related processes, its role in PNN remodelling (based on our preclinical data) and the paucity of data currently existing, we think there is a strong rationale for exploring the effects on 60 Hz in humans further. 2. At least one lower frequency should have been tested as a control. In the cited animal study (Venturino et al., 2021), 60 Hz—compared to 40 Hz—had a sp Attachments Attachment Submitted filename: Response to Reviewers_Alamalhoda et al.docx https://doi.org/10.1371/journal.pone.0332310.r002
20 Aug 2025 Decision Letter - Gennady S. Cymbalyuk, Editor <div>PONE-D-25-10411R1Exploring Neural Entrainment and Synchrony in Response to Repeated 60 Hz Flickering White Light in Healthy VolunteersPLOS ONE Dear Dr. ferretti, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please, address the following minor concerns:- In the abstract (line 35), there appears to be a typo: "flicking light across multiple cortical regions" should likely read "flickering light". - The naming of temporal channels is inconsistent throughout the manuscript and figures (e.g., sometimes Tp7-Tp8, Tp5-Tp6, or T5-T6). Please, unify this notation. - In the caption for SI Figure 6 (lines 1425-1427), the statement "The observed statistically significant differences are driven primarily by the large sample size (n), rather than any meaningful biological variation..." could be misleading. Please, clarify this point in the text to avoid confusion. Please submit your revised manuscript by Oct 04 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols . We look forward to receiving your revised manuscript. Kind regards, Gennady S. Cymbalyuk, Ph.D. Academic Editor PLOS ONE Journal Requirements: If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. [Note: HTML markup is below. Please do not edit.] 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 #1: All comments have been addressed Reviewer #2: All comments have been addressed ******** 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 #1: Yes Reviewer #2: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 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 #1: Yes Reviewer #2: Yes ****** 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 #1: Yes Reviewer #2: Yes ****** 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 #1: The authors have addressed my previous comments and improved the manuscript accordingly. A few minor suggestions remain: - In the abstract (line 35), there appears to be a typo: "flicking light across multiple cortical regions" should likely read "flickering light". - The naming of temporal channels is inconsistent throughout the manuscript and figures (e.g., sometimes Tp7-Tp8, Tp5-Tp6, or T5-T6). I advise unifying this notation. - In the caption for SI Figure 6 (lines 1425-1427), the statement "The observed statistically significant differences are driven primarily by the large sample size (n), rather than any meaningful biological variation..." could be misleading. I suggest clarifying this point in the text to avoid confusion. Reviewer #2: The majority of my concerns have been adressed and additional analyses included. As I understand that addiing further partcipants will not change the result I approve publication. ****** 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 #1: No Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0332310.r003
Revision 2
26 Aug 2025 Author Response - In the abstract (line 35), there appears to be a typo: "flicking light across multiple cortical regions" should likely read "flickering light". We thank the Reviewer for highlighting this typo. This has been corrected. - The naming of temporal channels is inconsistent throughout the manuscript and figures (e.g., sometimes Tp7-Tp8, Tp5-Tp6, or T5-T6). Please, unify this notation. Thanks for pointing us to this inconsistency. We have now edited the text throughout the manuscript, using T5-T6 to refer to temporal channels. - In the caption for SI Figure 6 (lines 1425-1427), the statement "The observed statistically significant differences are driven primarily by the large sample size (n), rather than any meaningful biological variation..." could be misleading. Please, clarify this point in the text to avoid confusion. We concur with the Reviewer that this sentence might have been misleading. We have now edited as follows: ´The statistically significant differences in PLV observed under constant light conditions are likely attributable to the large number of channel pair comparisons (n) rather than meaningful biological variation, since the average PLV values across groups and days remain comparable.´ Attachments Attachment Submitted filename: Second Response to Reviewers_Alamalhoda et al.docx https://doi.org/10.1371/journal.pone.0332310.r004
29 Aug 2025 Decision Letter - Gennady S. Cymbalyuk, Editor Exploring Neural Entrainment and Synchrony in Response to Repeated 60 Hz Flickering White Light in Healthy Volunteers PONE-D-25-10411R2 Dear Dr. ferretti, 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. An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support . 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, Gennady S. Cymbalyuk, Ph.D. Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0332310.r005
Formally Accepted
Acceptance Letter - Gennady S. Cymbalyuk, Editor PONE-D-25-10411R2 PLOS ONE Dear Dr. Ferretti, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. 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. You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Gennady S. Cymbalyuk Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0332310.r006

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