To Nap or to Rest? The Influence of a Sixty-Minute Intervention on Verbal and Figural Convergent and Divergent Thinking

Round 1

Reviewer 1 Report

Revision 1

The topic of this study is very interesting and little investigated. Although several studies have focused on the role of sleep in some cognitive functions such as memory, few studies have specifically investigated creative processes. However, there seems to be a strong relationship between sleep (specifically some stages of sleep) and creativity.

The results presented are interesting, unfortunately no significant results emerge in relation to the main hypothesis of the study, therefore it cannot be concluded that a period of sleep is more effective in determining a better creative performance than a period of rest (awake). In my opinion it would be interesting to make a comparison, within the group with the sleep intervention between REM and nREM participants, in fact it seems that the REM phase is particularly important for creativity. See for example the study by D'Anselmo et al, 2020, which finds interesting results on the relationship between narcoleptic symptomatology and creativity, where some narcolepsy symptoms strongly correlated to the dream phase seem to determine greater success and creative performance in these patients.

 

Below I list some recommendations that could contribute to the improvement of the work:

- pay more attention to the way in which the names of the great artists mentioned are written: Salvator Dalì and Leonardo da Vinci.

- the sentence “Somewhat contrary to these results, in their review Faraut et al. [17] reported a link between an increased prevalence of cerebrovascular diseases and regular and longer napping (>60 minutes) in elderly individuals.” seems poorly related to the concepts described above.

- In the introduction I recommend presenting the concept of convergent and divergent thinking, since the studies presented below on sleep and creativity describe both studies that have investigated divergent thinking and studies that have investigated problem solving tasks.

- “In this context, Drago et al. [24] studied the influence of REM and non-REM (NREM) sleep, on creativity performance as assessed by the Abbreviated Torrance Test for Adults 67 (ATTA).” In this study the results refer to the difference between REM and nREM this should be better explained.

- I suggest to the authors to describe the hypothesis of the study at the end of the paragraph of the Introduction.

- Line 151: “(Lenovo active pen)” could be removed since it was already described before.

- As for the results, I suggest describing them all in one paragraph and not divided by test. I also think it would be helpful for the reader to include a table of test scores.

- It would be interesting to do a further analysis to verify if there are differences between the participants of the sleep group, between nREM and REM.

- I was wondering if the differential effects obtained on the figural creativity tasks in the test with respect to the baseline could be due to the one-week interval that elapsed between these two moments, during which the participants could have continued to process information.

Author Response

The topic of this study is very interesting and little investigated. Although several studies have focused on the role of sleep in some cognitive functions such as memory, few studies have specifically investigated creative processes. However, there seems to be a strong relationship between sleep (specifically some stages of sleep) and creativity.

The results presented are interesting, unfortunately no significant results emerge in relation to the main hypothesis of the study, therefore it cannot be concluded that a period of sleep is more effective in determining a better creative performance than a period of rest (awake). In my opinion it would be interesting to make a comparison, within the group with the sleep intervention between REM and nREM participants, in fact it seems that the REM phase is particularly important for creativity.

See for example the study by D'Anselmo et al, 2020, which finds interesting results on the relationship between narcoleptic symptomatology and creativity, where some narcolepsy symptoms strongly correlated to the dream phase seem to determine greater success and creative performance in these patients.

 

We would like to thank the Reviewer for the positive feedback and for bringing our attention to the relevant paper by D'Anselmo et al, 2020, which we refer to in the revised Introduction.

 

 

Below I list some recommendations that could contribute to the improvement of the work:

 

- pay more attention to the way in which the names of the great artists mentioned are written: Salvator Dalì and Leonardo da Vinci.

 

Yes, indeed! We corrected the typos.

 

- the sentence “Somewhat contrary to these results, in their review Faraut et al. [17] reported a link between an increased prevalence of cerebrovascular diseases and regular and longer napping (>60 minutes) in elderly individuals.” seems poorly related to the concepts described above.

 

We reformulated this sentence. The idea was to also mention that naps may not always be beneficial.

 

- In the introduction I recommend presenting the concept of convergent and divergent thinking, since the studies presented below on sleep and creativity describe both studies that have investigated divergent thinking and studies that have investigated problem solving tasks.

 

We agree with the Reviewer. In the revised Introduction we added a passage detailing the concept of convergent and divergent thinking.

 

- “In this context, Drago et al. [24] studied the influence of REM and non-REM (NREM) sleep, on creativity performance as assessed by the Abbreviated Torrance Test for Adults (ATTA).” In this study the results refer to the difference between REM and nREM this should be better explained.

 

Thank you for this comment, we added more details about the difference between the REM and nREM effects found in this study.

 

 

- I suggest to the authors to describe the hypothesis of the study at the end of the paragraph of the Introduction.

 

Following the Reviewer’s suggestion, we moved the hypotheses to the end of the revised Introduction.

 

- Line 151: “(Lenovo active pen)” could be removed since it was already described before.

 

Thank you, this was corrected in the revised Methods.

 

- As for the results, I suggest describing them all in one paragraph and not divided by test. I also think it would be helpful for the reader to include a table of test scores.

 

This is a good idea. We have removed the subheadings of the “Between-group analysis”, and summarize its results in Table 2 of the revised results.

 

- It would be interesting to do a further analysis to verify if there are differences between the participants of the sleep group, between nREM and REM.

 

As suggested, for the nap group we compared the subjects with REM sleep versus subjects with nREM sleep. The REM subgroup included only 7 subjects, the nREM group included 17 subjects. Using Mann-Whitney non-parametric testing, we found no significant differences between the subgroups for the four creativity tests. This lack of significant differences may be due to the very small size of the subgroups.

 

- I was wondering if the differential effects obtained on the figural creativity tasks in the test with respect to the baseline could be due to the one-week interval that elapsed between these two moments, during which the participants could have continued to process information.

 

This assumption may be possible. Nevertheless, we found no hints with respect to such a mechanism in the literature. While one may speculate that participants “trained” during the one-week interval separating the sessions, the question arises as to which, why would this be the case for the figural but not for the verbal tests? Finally, the study participants did not receive any feedback concerning their performance in the baseline session, which further minimizes the wish to train performance.

 

 

Reviewer 2 Report

This is an interesting study that compares the outcomes of verbal and creativity tasks after either a nap or being awake in resting. The study did not find any differences between the two groups. The manuscript is well written. English is fine. The study, albeit very simple, was conducted without any significant flaws. Results were not remarkable, but still interesting to know that after all, a rest is good enough as a nap in terms of the tasks involved. Further metrics of cognitive tasks might be needed for a thorough assessment. But the current results and the study itself is well enough for reporting.

Author Response

This is an interesting study that compares the outcomes of verbal and creativity tasks after either a nap or being awake in resting. The study did not find any differences between the two groups. The manuscript is well written. English is fine. The study, albeit very simple, was conducted without any significant flaws. Results were not remarkable, but still interesting to know that after all, a rest is good enough as a nap in terms of the tasks involved. Further metrics of cognitive tasks might be needed for a thorough assessment. But the current results and the study itself is well enough for reporting.

 

We would like to thank the Reviewer for the positive evaluation of our study.

 

Reviewer 3 Report

Review Results

Manuscript entitled: To Nap or to Rest? The influence of a 60-minute intervention on verbal and figural convergent and divergent thinking

In this manuscript, the authors explain that the relationship between sleep and creativity is a topic of much controversy. Although several studies on napping have been conducted, only a few have investigated the relationship between napping and creativity. In this manuscript, 42 participants took part in two experimental sessions (i.e., baseline and intervention) with divergent and convergent verbal and figural creativity tasks. The authors found that no significant group differences were found for either divergent or convergent creativity tasks, suggesting that the interventions had similar effects in both groups. The authors recommend that further studies are needed to confirm these findings.

Generally, the authors try to explore the significance of napping in relation to creativity by linking it to human brain mechanisms. The authors tried to apply several methods and tasks but could not get the expected outcome. There are some issues concerning the methodology that might be the cause of unexpected outcomes.

Issue 1: In this study, 42 participants, with a mean age of 24 years old, participated in both experimental sessions. Why do the authors recruit younger participants but not older ones? What are the criteria the authors used while recruiting participants for whom the benefit of napping and creativity might be seen, i.e., shift workers, etc.?

Issue 2: In the PSG measurements as shown in table 1, the authors reported that the number of participants for the napping session was 24, while the resting session was only 18. The authors also mentioned that participants were randomized to either resting or napping sessions. As the total number of participants was 42, why did they not assign an equal number to each group? How were they assigned by randomized assignment?

Issue 3: In Table 1, the authors reported the percentage of each sleep cycle but did not report the number of participants involved. Why?

Issue 4: In Table 1, why do the authors report the outcome in percentage?

Issue 5: The authors mentioned that on the individual level, more than half of the participants assessed (i.e., 10 out of 24) were awake for more than 40% of the entire 60-minute nap time (range: 40%–79%). Where is this information in the manuscript?

Issue 6: The authors mentioned that, more importantly, 17 out of 24 participants showed no REM sleep, and N3 sleep was observed in 14 out of 24 participants. In which group? Where is this information in the manuscript?

In Issue 7: Line No. 279–280, the authors mentioned that indeed, the analysis of sleep stages indicated that in the nap group, barely 7 out of 24 participants had REM sleep and only 14 out of 24 had N3 sleep. How about the other stages? Is it possible to report these numbers in Table 1?

Issue 8: What is the purpose of applying the PSG measurement in this study? It seems the authors collected several important pieces of data, but some information was not linked to each other, causing the authors to conclude that their findings remain speculative.

After declaring all the above concerns, this manuscript might be re-reviewed for further decision.

Author Response

Manuscript entitled: To Nap or to Rest? The influence of a 60-minute intervention on verbal and figural convergent and divergent thinking

 

In this manuscript, the authors explain that the relationship between sleep and creativity is a topic of much controversy. Although several studies on napping have been conducted, only a few have investigated the relationship between napping and creativity. In this manuscript, 42 participants took part in two experimental sessions (i.e., baseline and intervention) with divergent and convergent verbal and figural creativity tasks. The authors found that no significant group differences were found for either divergent or convergent creativity tasks, suggesting that the interventions had similar effects in both groups. The authors recommend that further studies are needed to confirm these findings.

 

Generally, the authors try to explore the significance of napping in relation to creativity by linking it to human brain mechanisms. The authors tried to apply several methods and tasks but could not get the expected outcome. There are some issues concerning the methodology that might be the cause of unexpected outcomes.

 

Issue 1: In this study, 42 participants, with a mean age of 24 years old, participated in both experimental sessions. Why do the authors recruit younger participants but not older ones? What are the criteria the authors used while recruiting participants for whom the benefit of napping and creativity might be seen, i.e., shift workers, etc.?

 

The participants were recruited through the students’ pool of the University of Bern, which explains the mean age of 24 years. This information was added to the revised “Participants” section (section 2.1).

Our study started during the COVID-19 pandemic, which largely influenced the recruitment and deemed it impossible to recruit elderly participants. As it was not possible to recruit participants with a wide age-range (i.e., ranging from young adults to elderly subjects), we decided to restrict our sample to a homogenous group of university students. This choice is further supported by the notion that sleep behavior varies throughout life span, and sleep studies including participants of different age ranges shall address this phenomenon by carefully balancing the participants recruited.

 

Issue 2: In the PSG measurements as shown in table 1, the authors reported that the number of participants for the napping session was 24, while the resting session was only 18. The authors also mentioned that participants were randomized to either resting or napping sessions. As the total number of participants was 42, why did they not assign an equal number to each group? How were they assigned by randomized assignment?

 

Yes, we do not have equal sample sizes. This is due to the randomization procedure applied in this study, i.e., simple (unrestricted) randomization. When we realized that both samples will not have equal group sizes, we did a literature search whether unequal group sizes may pose an issue for the study. We found a paper by Schulz and Grimes, two eminent epidemiologists, which was published 2002 in Lancet with the provocative title “Unequal group sizes in randomised trials: guarding against guessing”. Concerning unequal sample sizes let us cite their statement: “We cringe at the pervasive notion that a randomised trial needs to yield equal sample sizes in the comparison groups. Unfortunately, that conceptual misunderstanding can lead to bias by investigators who force equality, especially if by non-scientific means. In simple, unrestricted, randomised trials …  some discrepancy between the numbers in the comparison groups would be expected. The appeal of equal group sizes in a simple randomised controlled trial is cosmetic, not scientific.”

 

We therefore abstained from adding participants in the rest group to obtain equal group sizes.

 

Reference: Kenneth F Schulz, David A Grimes. Unequal group sizes in randomised trials: guarding against guessing. Lancet 2002; 359: 966–70

 

 

 

Issue 3: In Table 1, the authors reported the percentage of each sleep cycle but did not report the number of participants involved. Why?

 

Thank you for the comment. We have added the number of participants to the revised Table 1. We have also added a supplementary Table S1a that reports the number of participants from the nap group, who reached the different sleep stages. This may help clarifying some Issues raised by the Reviewer, and which are also addressed below (points 4-7). Also, following Reviewer’s 1 suggestion, we have rewritten section 3.2. of the revised Results.

 

 

Issue 4: In Table 1, why do the authors report the outcome in percentage?

 

We believe that reading percentages is easier for the reader than to comparing the duration in minutes. For the sake of completeness and clarity, in the revised manuscript, next to percentages, we also report participant numbers.

 

Issue 5: The authors mentioned that on the individual level, more than half of the participants assessed (i.e., 10 out of 24) were awake for more than 40% of the entire 60-minute nap time (range: 40%–79%). Where is this information in the manuscript?

 

Thank you for spotting this mismatch. We have corrected this sentence and added a supplementary Table S1a reporting more details.

 

Chapter about individuals and Duration

 

Issue 6: The authors mentioned that, more importantly, 17 out of 24 participants showed no REM sleep, and N3 sleep was observed in 14 out of 24 participants. In which group? Where is this information in the manuscript?

 

We have clarified this in the revised section 3.1 and added it in the supplementary  Table S1a.

 

 

In Issue 7: Line No. 279–280, the authors mentioned that indeed, the analysis of sleep stages indicated that in the nap group, barely 7 out of 24 participants had REM sleep and only 14 out of 24 had N3 sleep. How about the other stages? Is it possible to report these numbers in Table 1?

 

This is a good idea; this is information is now included in the revised Table 1

 

 

Issue 8: What is the purpose of applying the PSG measurement in this study? It seems the authors collected several important pieces of data, but some information was not linked to each other, causing the authors to conclude that their findings remain speculative.

 

The purpose of the PSG measurement in our study was to include an objective parameter for the quality of the nap and  the rest behavior. We believe that the data of the PSG measurement not only quantifies the macrostructure of the interventions (among others ensuring that the participants in the rest condition stayed predominantly awake), but it also provides an important piece of information that may help explaining the effects observed. We discuss that the nap condition may not have been optimal, i.e., large percentage of wake, and N3 and REM sleep that were not present in all participants of the nap group, which may possibly explain the lack of significant group differences.

Since the finding concerning the differential effects of the intervention on figural and verbal creativity is novel (i.e., has never been described to date), we prefer to stay careful in the interpretation.

 

 

 

Round 2

Reviewer 1 Report

The changes to the manuscript are exhaustive for me.

Reviewer 3 Report

It seems the authors can answer all of my conserns and clarify what I was questioning to them, especially the their research methodology. However, there is a limitation of this study, but the authors can keep further study on it especially the PSG data in order to confirm their current findings.