PONE-D-24-32615Assessing white matter plasticity in a randomized controlled trial of early literacy training in preschoolersPLOS ONE

Dear Dr. Caffarra,

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“SC conducted this research as part of the projects FAR Mission Oriented 2022 and PRIN PNRR 2022 P2022SMEJW, which were funded by the European Union – Next Generation EU. IK was supported by the Stanford Maternal and Child Health Research Institute award. AR and JK were funded by NSF grant 1934292 and NIH grants RF1 MH121868 and R01EB027585. JK was additionally supported through the NSF Graduate Research Fellowship DGE-2140004, NIH grants R21HD092771 and R01HD095861.”

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Additional Editor Comments:

This work has now been reviewed by two experts in the field. While both reviewers felt that this work addresses an important topic, they have several suggestions to improve context, clarity and interpretation.

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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: Yes

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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?

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Reviewer #1: No

Reviewer #2: No

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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: Reviewer Comments

The manuscript “Assessing white matter plasticity in a randomized controlled trial of early literacy training in preschoolers” describes a randomly controlled trial which showed literacy skill improvement in preschool children who participated in letter-focused literacy training, but not those who participated in oral language training. This study supports the efficacy of short-term literacy training in typically developing children. No corresponding changes in diffusion-tensor imaging metrics of white matter microstructure were found. This study fills a gap in the literature, which has mainly focused on training and intervention programs for children with or at-risk for reading disabilities. This manuscript would benefit from further development of the methods to provide clarity. My specific comments are detailed below:

Major Comments:

1. Were the same versions/forms of the assessments used for behavioral assessment before and after the training period? Were any measures taken to account for practice effects on the assessments?

2. Please provide a detailed description of the statistical analysis (LME models for both behavioral and dMRI measures) in the Methods section. How many total models were tested? Were multiple comparisons controlled? Were any model fitting parameters computed to verify whether including random slopes improved model fit (was there substantial random effects variance in the models)? Please also justify why random slopes were included in the behavioral models but not the dMRI models. Sharing code would be helpful here.

3. Were any analyses conducted to test whether the groups were well-matched on language and reading abilities at baseline? Were the numbers of males and females matched across groups (This is relevant given that girls tend to perform better than boys on language measures at this young age)? It would be helpful to include a table indicating the demographic and behavioral characteristics of the groups prior to training, including whether the time between MRI sessions and training (pre & post) were similar across groups.

4. The distinction between the “profile reliability” and “subject reliability” is not clear. Specifically, please clarify what value(s) is used to calculate profile reliability and what is meant by “tract profile”. Is an average taken across nodes to calculate this reliability, or does the profile reliability describe reliability within nodes across participants?

5. Please clarify in the Results whether there were any significant main effects of time (i.e., improvement regardless of training group).

6. In the methods section, it is stated that DTI metrics were weighted by streamlines’ distance from the tract core. Based on examination of the tract profiles, FA values at the tails are much lower than along the main body of the tract; some tracts (e.g. ILF) show extremely high values for MD at the tails. Was any weighting applied to account for averaging across nodes along the tract to account for distance from the central node and the extreme FA/MD values observed at the tails for many tracts?

7. For the follow-up analysis “Linking training effects between behavioral and dMRI measures”, please clarify why this analysis focused only on alphabet knowledge (not other behavioral measures) and only on the left AF and ILF. Please also include a description of this analysis in the methods section.

8. In the discussion, please consider whether the lack of dMRI affects in this typically developing preschool sample could be because the children’s brains are already well-wired for reading before formal reading instruction begins. This would be consistent with evidence that white matter differences in children with and without (risk for) dyslexia are observed prior to formal reading instruction, and even in infancy. Thus, dramatic and rapid reading-instruction-related white matter plasticity may not be expected in this sample, in contrast to children at risk for dyslexia who may require white matter adaptation to support development of an adequate reading network.

Minor comments:

1. In the introduction, only the AF and ILF are introduced as important tracts for reading, however, several other tracts have been linked to reading and this study includes 18 white matter pathways within and outside the reading network. Additional tracts including the SLF and IFOF should be mentioned.

2. Table 1 provides a helpful summary of the prior literature, it would be useful to index the papers by author & year in addition to the reference numbers.

3. In the “behavioral data acquisition” section (page 11), please include the names of the full assessments in the main text along with their citations.

4. Please provide a reference for the OASIS target template (page 12).

5. In Figure 1, it appears that pre-training and post training sessions occurred immediately at the onset and completion of the 2-week training. For clarity, please show in the figure that these sessions occurred over a range of time prior to and after training.

Reviewer #2: This randomized controlled study investigated the effects of two training programs—language and literacy—on reading-related skills in English-speaking preschoolers. The authors evaluated behavioral outcomes and changes in white matter integrity using diffusion MRI (dMRI) metrics, specifically fractional anisotropy (FA) and mean diffusivity (MD) across 18 white matter tracts, including the left arcuate fasciculus and left inferior longitudinal fasciculus. Forty-eight preschoolers (mean age 5 years) were randomly assigned to either a Letter Program or a Language Program, both conducted in a summer camp format over two weeks, totaling 30 hours of training. Behavioral and MRI data were collected before and after the intervention.

Linear mixed-effects models revealed a significant interaction between Training Type and Time for alphabet knowledge and decoding skills. Post-hoc analyses indicated that children in the Letter Program showed significant improvements in both alphabet knowledge and decoding skills, whereas no such effects were observed in the Language Program. In contrast, dMRI analyses showed no significant interaction effects or main effects of Time or Training Type, indicating no structural changes in the white matter. Bayesian analyses further supported the null hypothesis, with Bayes factors providing small-to-moderate evidence against structural changes in most of the white matter tracts examined.

Given the limited research on structural brain changes in typically developing preschoolers, this study contributes to the literature by showing that a relatively short, intensive intervention (30 hours over two weeks) can lead to behavioral improvements without corresponding structural changes in the brain. These findings highlight the need for further research to explore how the duration and intensity of interventions impact both behavioral outcomes and brain structure over time.**

Suggestions for Strengthening the Manuscript:

Introduction:

The study's hypotheses and predictions are not clearly articulated. In Table 1, only Study [3] reported structural changes in preschoolers following a reading intervention, while another study in the same age group did not. Other studies listed in Table 1 reported structural changes only with higher dosage interventions (>100 hours) and in school-aged children. It would be helpful to clarify whether structural changes were anticipated in this study's preschool cohort, particularly in relation to findings from [21] and [20]. Although the two-week, 30-hour intervention is intensive for preschoolers, the relationship between dosage, intervention length, and observed effects should be more explicitly discussed. Clarifying these concepts, as well as outlining the study's hypotheses and predictions, would enhance the theoretical framework of the manuscript.

Participants:

To better contextualize the sample, the manuscript should provide demographic details, including the mean age (with standard deviations) and gender distribution for both groups. Although the inclusion criteria are well defined, it is unclear whether the groups were balanced on behavioral measures before the intervention. Presenting descriptive statistics for pre-intervention behavioral measures would clarify this. Additionally, the authors should explicitly confirm whether raw scores were used for analyses. It would be beneficial to include both pre- and post-intervention descriptive statistics for all behavioral measures, even for those that did not show significant changes. Including effect sizes is critical, as this would help address whether the absence of structural changes is due to the short intervention period or because the treatment effect was too small to induce measurable structural changes.

Program Fidelity:

The manuscript would benefit from more details on how program fidelity was assessed to ensure that the training was consistently delivered across participants.

Measure and Figure:

It is unclear which task the authors refer to as “decoding skills” in the results. Is this referring to the phonological awareness literacy screening task? Regarding Figure 2, distinguishing between uppercase and lowercase letters may not add value if the analysis is based on their average score. Since significant results were found for alphabet knowledge (using the average score of uppercase and lowercase letters) and decoding skills, it would be more informative to present these two variables in the figure.

Results and Interpretation (Linking Training Effects to dMRI Measures):

The factor controlled for in the Bonferroni correction in Table 3 is not clear. Providing a more detailed explanation of the correction method would enhance clarity. Additionally, given that the correlation coefficients (-0.38, -0.41, 0.36) are moderate, the non-significant results could be attributed to the limited sample size. Since correlation coefficients can be interpreted as effect sizes, these moderate values suggest the potential need for further exploration. The authors may consider running Bayesian analyses as a validation step to provide additional insight into these findings.

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Reviewer #1: No

Reviewer #2: Yes: Silvia Clement-Lam

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PONE-D-24-32615R1Assessing white matter plasticity in a randomized controlled trial of early literacy training in preschoolersPLOS ONE

Dear Dr. Caffarra,

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.

 Both reviewers feel that the manuscript is substantially improved and have requested only very minor changes in a revision.

Please submit your revised manuscript by Jan 24 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,

Signe Bray

Academic Editor

PLOS ONE

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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.

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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: (No Response)

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 #1: Yes

Reviewer #2: Yes

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

Reviewer #1: Yes

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 #1: No

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 #1: Yes

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 #1: The reviewers have carefully addressed all of my initial queries. I have several small suggestions pertaining to the revised version of the manuscript:

Data Availability: I attempted to access the data at doi: 10.18112/openneuro.ds005572.v1.0.0 and received the error “403: You do not have access to this page, you may need to sign in.” I was still unable to access the data after signing in with my ORCID.

Table 2.

- Typo: Post MRI-camp time different (days)

- Please indicate whether Raw or Standard/Scaled scores are reported (also for the PPVT inclusion criteria, p.8 l. 147).

Methods

- Please cite software and packages used for statistical analysis.

- Thank you for providing additional clarity regarding the reliability analyses. The inclusion of scan-rescan reliability analysis conducted over the two experimental sessions seems counterintuitive given the hypothesis that the DTI metrics would change rapidly with reading training. In other words, if the results had shown significant training-related changes in DTI measures, the reliability tests would not have shown strong scan-rescan reliability. I suggest further justification and discussion of the reliability analysis, or restructuring to include the reliability analysis in the supplementary materials to show the stability of the DTI metrics over time, rather than as a preliminary analysis. Otherwise, please clarify if I am misunderstanding the implementation of the reliability analysis in this study.

Results

- Please clarify the direction of change in left ILF FA that is potentially associated with Alphabet Knowledge improvement. The statement that “BFs signaled a moderate support for the presence of a link between Alphabet knowledge improvement and an FA reduction of the left ILF (BF>3).” (P. 23, lines 392-394) seems to indicate that children who improved more on Alphabet knowledge showed a decrease in FA of the left ILF over time, but this does not seem to be consistent with the explanation in the text or the response to Reviewer 2, in which it seems that the negative correlation between Alphabet Knowledge change and FA change indicates that children with greater Alphabet Knowledge improvement showed smaller increases in FA. It would be helpful to include Figure S3 in the main text to support interpretation of these results.

Reviewer #2: The authors have made a commendable effort in addressing the feedback provided by the reviewers. I have minor feedback regarding the description of the behavioral measures: instead of combining everything into one paragraph, I suggest listing the measures separately for greater clarity and readability.

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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.

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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: Yes: Silvia Clement-Lam

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[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.]

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Assessing white matter plasticity in a randomized controlled trial of early literacy training in preschoolers

PONE-D-24-32615R2

Dear Dr. Caffarra,

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.

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Signe Bray

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments: