The Effect of Circadian Photoreceptors Stimulation on the Stress Response of Subjects with High Anxiety: A Pilot Study

Round 1

Reviewer 1 Report

The manuscript “The Effect of Circadian Photoreceptors Stimulation on the Stress Response of Subjects with High Anxiety” studied the impact of circadian system activation on heart rate variability in female medical students with high anxiety while performing a cognitive task. I have identified several areas that need to be addressed before the manuscript can be considered for publication.

Firstly, the statistics used in the study are based on a small sample size of only 17 female students. This limitation raises concerns about the reliability and generalizability of the findings. I suggest expanding the sample size to enhance the statistical power of the results.

Secondly, while the authors present the results by statistical analysis, there is a lack of possible biological mechanisms that can explain the changes upon the blue light stimulation. I recommend that the authors provide more information on the underlying mechanisms that could account for the observed outcomes.

Lastly, the timing of the cognitive task is a crucial factor that should be considered in the experiment. As the research is about the impact of circadian system activation, it is essential to consider the timing of the cognitive task in relation to the participants' circadian rhythms. Thus, it is essential to evaluate the impact of the timing of the cognitive task on the results.

In conclusion, I recommend that the authors address these concerns before resubmitting the manuscript for further consideration.

Author Response

Dear Reviewer!

Thank you for your suggestions to improve the quality of the manuscript of our paper.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Major concerns and suggestions to improve the manuscript:

This manuscript shows that blue light exposure produces HRV modulation in subjects with high anxiety levels during cognitive tasks. However, although this finding is interesting, the authors wrote their manuscript assuming that the blue light stimulation with “Blue Sky Pro glasses” affected the circadian and autonomic nervous systems and the psycho-emotional and cognitive functions. Hence, the authors wrote a narrative throughout the entire manuscript regarding these systems and their relationships, neglecting the original experimental variables and parameters (blue light exposure with the Blue Sky Pro glasses and HRV parameters; the data shown in the results section).

The manuscript could be of interest in diverse interdisciplinary fields and relevant to this journal; however, it requires improvements by rewriting the manuscript in plain terms, just modifying the title, abstract, and introduction in terms of the effects of the intervention with a blue light on the HRV parameters. In addition, the authors could send all the speculations described in the title, abstract, and introduction to the discussion section, in which it is possible to make speculations regarding the circadian and autonomic systems and proposals for future experiments to demonstrate them.

 

Specific concerns:

-The authors should include the units and number of samples in all figures and tables.

-In the abstract, the authors wrote the terms “monochromatic blue light” and “Blue Sky Pro glasses” without mentioning they are synonyms. Therefore, this reviewer suggests using only one of both terms to avoid the necessity to read the methods section to understand the abstract.

-The intensity of the emitted blue light with the Blue Sky Pro glasses was not mentioned. Please mention the intensity of light exposure in units of optical power (Watts units). Which is the temperature of the emitters during 20 minutes? Which kind of emitters did the authors employ? Are there photodiode LEDs? Which model of LED was employed? How many of them were mounted on the glasses? Is there a safety certification to use these photodiodes on the Blue Sky Pro glasses?

-How could the results in this manuscript change if the light exposure is increased or decreased; please comment in the discussion section?

-Lines 151, 179-180, and 189-191. These sentences in the results section are speculative and not directly associated with the results illustrated in figures and tables.

-The cited references in the Methods section supporting that “melanopsin-containing retinal ganglion cells were stimulated using the Blue Sky Proglasses” (11 and 12) are not related to this claim, which makes this assumption a speculation. Reference 11 is just a patent and reference 12 is a Russian article with a translated title: “Control of the management of the functional state of the human body by the circadian system in the early morning hours.” This manuscript does not directly obtain electrophysiological recordings of specific ”melanopsin-containing retinal ganglion cells” that could be stimulated using these Blue Sky Pro glasses. This claim could be sent to the discussion section, mentioning the potential uses of this type of glasses.

-Only a single sentence in lines 327-329 mentions the limitations. The authors could include a limitations section to provide arguments of potential experiments to demonstrate that blue light exposure with “Blue Sky Pro glasses” could affect the circadian and autonomic nervous systems, as well as the psycho-emotional and cognitive functions. Here the authors could also include the limitation of the necessity to examine optimal light intensities and the low sample of subjects.

Minor editing of English language required

Author Response

Dear Reviewer!

Thank you for your suggestions to improve the quality of the manuscript of our paper.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors Sergeeva et al present results from a study wherein they investigated the effects of blue light on HRV and other stress parameters during the execution of a cognitive task in 17 selected female volunteers prone to anxiety. 

My comments are:

- Please revise the entire introduction and provide a clearer path to your study. The introduction of circadian clock genes does not at all fit to the contents of your study. CLOCK  or BMAL1 were not studied. Also the neuron morphology of the prefrontal cortex was not investigated in this study population.  

Materials/Methods:

- Please place your ethics statement first before all other explanations

- Provide a clearer explanation why you only chose 17 females and no men. To generate a homogeneous group is not really an explanation. If none of the male volunteers fit the parameters than this fact needs to go to the section of study limitations. 

- There are several flaws in the study design since you did not control for pre-test anxiety and test experience in this study. You select subjects that are prone to test anxiety, therefore it can be expected that the first time they perform the test, anxiety is higher than during the second time after the blue light. It is also possible that relieve happens after the end of the first test which produces a significant bias to the "effects of blue light". During the second time of the test, the subject knows the situation and therefore is per definition less stressed. A cross-over design would have been an alternative and better choice.  Moreover, this study lacks of a control group of females not prone to anxiety further limiting the study results.

These flaws need to be addressed to be able to evaluate the results properly. If a control group is not possible, than an critical discussion of the results is necessary together with a very clear description of all limitation.

Discussion:

-The discussion reads more like a review than like a discussion, please discuss in detail what your results mean compared to what is known.

- The section of the study limitations needs to be expanded to cover all the methodological limitations and the small study population. 

Author Response

Dear Reviewer!

Thank you for your suggestions to improve the quality of the manuscript of our paper.

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

While the authors added some limitations regarding the small sample size in the revised manuscript, I still maintain that a statistically significant conclusion cannot be drawn from data collected from only 17 individuals. 

Therefore, I suggest that the authors consider expanding their sample size or modifying their research design to address this concern.

Author Response

Dear Reviewer!

Thank you for your suggestions to improve the quality of the manuscript of our paper.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have satisfactorily responded to all my comments.

Author Response

Dear Reviewer!

Thank you for your suggestions to improve the quality of the manuscript of our paper.

Reviewer 3 Report

The Introduction has improved and the limitation section has been expanded.

The lack of the control group is still an issue that limits the conclusions that can be drawn from the observed results. Please provide a statement exactly why you are unable to investigate a control group and add the data.

Author Response

Dear Reviewer!

Thank you for your suggestions to improve the quality of the manuscript of our paper.

Please see the attachment.

Author Response File: Author Response.pdf