The Intention to React to Sounds Induces Sleep Disturbances and Alters Brain Responses to Sounds during Sleep: A Pilot Study

Round 1

Reviewer 1 Report

This study investigated the effect of pre-sleep intention to react to auditory stimuli in 26 subjects, divided in two groups (“sound” group, “no sound” group), and in different conditions (“on call” condition, “neutral” condition).

The authors found that the instruction to be “on call” altered objective sleep quality (decreased sleep efficiency, increased time spent awake and the number of awakenings, with more N1 and less N3) compared to the control condition, and this independently of sounds physically present during sleep or not. They also analyzed many other parameters, but they did not find differences in subjective sleep quality, power analysis, heart rate variability, indicators of parasympathetic and sympathetic activity, vigilance or memory consolidation due to the “on call” instruction.

Unfortunately, reaction time to stimuli in both conditions could not be analyzed, but it is without doubt an original piece of research, well conducted and also well written, which shows that voluntary focusing of attention seems to be preserved during sleep, and address important questions for the consequences for real-life « on call situations ». I don't have major comments.

Minor/typos:

see Figure 1, or an overview of the procedure  >> see Figure 1, for an overview of the procedure

2.3. EEG Power Analysis : the main effect reached a statistical trend (F(1,24)=3.84, p=062, n2 = 0.12; (See Table 2). >>> the main effect reached a statistical trend (F(1,24)=3.84, p=.062, n2 = 0.12; (See Table 2).

Author Response

We thank the reviewer for his/her positive evaluation of our manuscript. And we would like to say special thanks for his/her careful reading. We corrected the typos spotted by the reviewer.

Reviewer 2 Report

This pilot study taps on a very central aspect of sleep – conscious information processing capacity. It replicates the study of Wuyts and colleagues but adds a central methodological aspect to it by the randomized interplay of expectations on sounds and actual sounds heard during night. The study tests the assumption that presleep intentions to be on call affect the sleep quality independently of the experimental sleep disturbance. In contrast, presentation of the same sounds without the instruction to react will cause no, or only minor, sleep impairments. The research question is well-motivated and soundly supported by literature on the topic.

The results are well outlined with adequate details.

The FDR correction would be recommendable though due to the long list of analyses done. if not used, please argument.

As stated in Figure 2 text, the sleep efficiency parameter is actually reducible to WASO, as the sleep latency was not affected – please reconsider its usefulness then.

Please remove a doubled sentence: We extracted the mean power of different frequency bands for each brain hemisphere. We  extracted the mean power of different frequency bands for both brain hemisphere separately.

While the amount of sleep stages did not differ in great extent between the conditions, a way to analyze the data further would be using sleep stage transition probabilities – or, it too demanding statistically, the length of continuous stage duration. Would the sleep be more fragmented in relation to stage transitions if “on call”?

The discussion is well-targeted and efficient. However, a wider implication related to the question of sleep and consciousness  is not focused? I was also longing for suggestions for some future lines of research, not only focused on increasing sample sizes or increasing ecological validity.

Were there any participants so disturbed that their sleep was interrupted for longer (to be defined) periods?

Methods:

Did you see any “friend of the experimenter” effect in sleep quality or other central parameters?

How did you define the stage after the two humans and one automated algorithm (?siesta?) doing their job? What was the interrater and human-machine correlation?

The justification for analyzing only N2+N3 power (not REM) is missing?

In summary, the pilot study is well-performed with sound design and methodological choices. The data analyses and indicators are well-justified, and in their well-thought simplicity, the design and results contribute essentially to understanding consciousness in sleep.

Author Response

Please see the attachement.

Author Response File: Author Response.pdf