The effects of prolonged single night session of videogaming on sleep and declarative memory.

Use of electronic media is widespread among adolescents. Many male adolescents spend a major part of their evenings playing video games. The increased exposure to artificial light as well as the exciting nature of this pastime is under suspicion to impair sleep. Sleep is considered to be important for memory consolidation, so there is also a potential risk for memory impairment due to video gaming. As learning and gaining knowledge is a very important part of adolescence, we decided to study the effects of prolonged video gaming on sleep and memory. The study was structured in a repeated measures design. Eighteen male participants played either the violent video game "Counter Strike: Global Offensive" or the board game "Monopoly" for five hours each on two Saturday nights. The game evenings were followed by sleep studies. Memory testing and vigilance evaluation was performed the next morning. During the course of the study, saliva samples were taken to determine melatonin and cortisol levels. The results of this crossover study showed slightly reduced sleep efficiency after "Counter Strike: Global Offensive" (-3.5%, p = .017) and impaired declarative memory recall (p = .005) compared to "Monopoly". Melatonin levels at bedtime were lower after "Counter Strike: Global Offensive" (p = .005), cortisol levels were elevated while playing the video game (p = .031). Negative effects on sleep were not strong but consistent with more wake after sleep onset (+12 min) and a higher arousal index after "Counter Strike: Global Offensive". We conclude that excessive video gaming in the evening can contribute to worsened sleep and impaired memory in male adolescents.

Introduction

Usage of digital media is a part of the day-to-day life in industrialized countries [1]. Children's and adults’ free time is largely spent using smartphones, computers and games consoles [2-4]. The innovation of electrical light and later the intense use of digital media is another general behavioral change, humans have not been geared for by evolution and which has potential effects on sleep, wellbeing and learning performance [5]. Artificial light during the dark phase is known to impair melatonin secretion. This is especially true for light emitted by electronic screens which typically contains bluish light known to affect the internal clock and impair sleep quality [6]. Playing violent video games requires intense continuous screen observation. A recent large scale study [7] has shown, that 70% of the German male and 16% of the female adolescents play video games almost every day. 163 minutes of average gaming time per weekend day and 124 minutes per week day have been reported for male adolescents. In 2013 the American Psychiatric Association included Internet Gaming Disorder (IGD) in section III of the Diagnostic and Statistical Manual (DSM-5) [8]. The Worlds Health Organization also included Gaming Disorders in the actual version of the International Classification of Diseases (ICD-11) [9]. The measurement instruments and the consequences of Gaming Disorders are widely debated [10, 11]. Studies investigating video gaming (gaming time between 50 and 165 minutes) and sleep have shown variable effects on sleep and stress, the latter typically expressed as heart rate changes [12, 13]. Further studies showed inconclusive effects on sleep; most of them showed a modest effect [12, 14, 15]. Cortisol levels after videogaming were typically not higher than before videogaming [16] but until now cortisol levels during videogaming have not been measured. Sleep is closely associated with memory function and cerebral development of adolescents [17, 18]. Declarative learning and consolidation of knowledge is a key factor for successful school performance. Memory consolidation can be modulated by interfering activities between acquisition and reproduction. There is evidence for external disturbers like videogames or music during learning breaks [19] and also internal factors like cortisol levels [18, 20] interacting with memory consolidation. To our knowledge, there is no conclusive data about the effect of prolonged evening video gaming on memory function. Working in clinical sleep medicine we noted an increase in circadian sleep-wake-rhythm-disorders, type delayed sleep phase, over recent years, especially in male adolescents and young adults. Many of these patients reported excessive gaming time sometimes >8 hours per day, even on weekdays. We therefore decided to investigate effects of rather long gaming times. This study aims to collect data on the effects of prolonged time playing “Counter Strike: Global Offensive” (300 minutes) compared to playing “Monopoly” for the same duration in the evening before bed time. Measures included sleep (polysomnography), declarative memory performance, cortisol and melatonin levels, sleepiness and vigilance. Our main questions were:

Does prolonged videogaming (“Counter Strike: Global Offensive”) have a notable effect on sleep efficiency?

Is there a difference in sleep-dependent post-sleep declarative memory recall between the “Counter Strike: Global Offensive” and “Monopoly” condition?

In addition, we aimed to describe and compare:

Cortisol levels during the study procedures; cortisol during “Counter Strike: Global Offensive” and during playing “Monopoly” was of special interest.

Melatonin levels during the study procedures, especially at bed time.

Vigilance in the morning after study nights.

Differences in declarative memory performance directly after the “Counter Strike”/ “Monopoly” stimulation

Methods

Ethics

Ethic committee Marburg (Az.82/15) approved this study. All participants were informed in writing about the study and gave their written consent.

Participants

Twenty male adolescents between 16 and 18 years of age were recruited via an article in the local newspaper. Regular school attendance, habitual daily video gaming and experience with violent video games were inclusion criteria. Preexisting sleep disorders, neurological disorders, cardiac diseases and regular intake of prescription medication led to exclusion. An introducing interview showed an average time in bed of the participants of 7,65±0,57 hours during the week and 9,02±1,26 hours at the weekend. Participants received 100 € remuneration for successful study completion. In case of participants aged under 18 the parents or guardians had to give their consent. Two participants discontinued the study because they felt it was too time-consuming, so eighteen participants (mean age 16.84 years) completed the study.

Procedures

Investigations took place between September 2015 and February 2016. Each participant passed three study weekends. The first weekend served as habituation phase. Habitual sleepiness was measured (Epworth-Sleepiness-Scale [21]) at 6 PM on Saturday. Between 6 and 7 PM, the polysomnographic montage according to American Academy of Sleep Medicine (AASM) criteria [22] was attached. Participants were allowed to spend the evening in the sleep lab in whatever way they wished, which was typically either reading or watching TV. Between midnight and 7 AM on Sunday morning, polysomnography (PSG) was performed with Embla N7000 systems (Natus Medical Incorporated, San Francisco, CA.). During the following weekend, study procedures started at 3 PM on Saturday. After application of the PSG montage, all subjects underwent a memory test (Verbal Learn and Memory Test, VLMT [23]). The VLMT consists of two lists, each with fifteen unrelated words (list A and list B). There is a parallel form for repeated testing. List A is read out by the investigator in five consecutive learning trials, each followed by an immediate free recall by the participants. This is followed by one round of reading and immediate recall of the distractor list. After the “Counter Strike: Global Offensive” resp. “Monopoly” stimulation (pre-sleep) and on Sunday morning (post-sleep) the participants were asked to recall the words from list A. There was no exact time limit for the recall, but it usually lasted less than one minute until subjects stated that they recalled no further words. There was no feedback about the number of correct recalled words. Between 6 PM and 11 PM, four to five subjects jointly played either the board game Monopoly (HASBRO Deutschland GmbH, Dreieich) or the video game „Counter Strike: Global Offensive”(Valve, Bellevue, WA, recommended for players not younger than 16 years). Monopoly is a classic board game with the goal of earning the most money in comparison to the other players. “Counter Strike: Global Offensive” is one of the most popular video games and often played by adolescents. It´s a first-person shooter video game and the gamers are divided into a terrorist and a counter-terrorist team. Usually there are two different scenarios. The terrorists have to plant a bomb or defend the hostages while the counter-terrorists need to prevent planting or defuse the bomb or rescue the hostages. 50% of the participants played “Monopoly” on the second weekend and the video game on the third weekend, the other half played in reverse sequence (Sequence 1: Counter Strike/Monopoly; Sequence 2: Monopoly/Counter Strike). The two parallel forms of the VLMT were used for the two study weekends and subjects were informed about the planned recalls on both weekends. Unfortunately, the two drop-outs were both in group sequence 2 but in all it was nearly balanced (Sequence 1: ten data sets, Sequence 2: eight data sets). The participants were offered pizza and snacks in the evening. When playing a game for five hours was too exhausting for a participant, he was motivated to continue so none of the adolescents had to stop playing during the measurements. During video gaming, participants were subjected to 45–55 lux light intensity at eye level from the PC screens. Ambient light intensity during the board game was around 20 lux at eye-level. After playing games, participants got ready for the night and PSG recordings were started (lights out) around midnight in single room sleep labs. Lights on was at 7 AM. Subjects filled in the Stanford Sleepiness Scale [24] to evaluate current sleepiness 30 minutes after lights on. Subsequently they underwent the pupillographic sleepiness test (PST) [25] and the vigilance test VigiMar [26]. For the 11-minutes PST, pupil diameter variations indicate vigilance, whereas mean reaction time over a monotonous 90 minutes four choice reaction time test is used as vigilance measure of the VigiMar. In order to determine cortisol and melatonin concentration, five saliva samples were taken at 5.45 PM, during a short gaming break at 9.07 PM, after gaming at 11.37 PM, during nocturnal rest at about 2.10 AM and after lights on at 7.28 AM. To minimize sleep disruption, the fourth nocturnal saliva sample was taken only when subjects were currently not in REM or slow wave sleep, so sample times were more variable than for the other saliva samples (2.10 AM ± 19 minutes). While collecting the nocturnal sample the ceiling light was not switched on.

Fig 1 gives a temporal overview for the study weekends two and three.

Fig 1

Temporal overview of measurements.

VLMT- Verbal Learn and Memory Test.

Data analysis

Polysomnographic recordings were analyzed visually according to standard criteria [22] by trained and certified (German Sleep Society) sleep technicians. Results of memory testing (VLMT) are determined by adding up the number of correct words recalled. The maximum attainable score is 15 (all words recalled). Pupil diameter variations are expressed as pupillary unrest index (PUI). High PUI values are computed by the PST system to indicate low vigilance. The VigiMar test computes mean reaction time over the test. Slow reaction time indicates low vigilance. Melatonin was measured with the ELISA-SLV-4779 enzyme immunoassay salivary kit. Active free cortisol levels were determined with the salivary kit HS ELISA-SLV-4635 (both kits DRG International Inc).

Statistical analysis

Statistical Analysis was done with SPSS version 22 (IBM corporation). All variables were tested for normality by Kolmogorov-Smirnov one sample testing. Most variables showed deviations from a normal distribution. We therefore decided to use robust non-parametric methods for all statistical testing. As most studies in this field report results that are expressed as means and standard deviations, we decided to use these measures along with median and quartiles for descriptive purposes in order to facilitate comparisons of our results to the literature. All tables therefore contain mean and standard deviation as well as median and 1st and 3rd quartile. Our study addresses two non-independent main issues (issue 1: sleep efficiency, issue 2: declarative memory). Bonferroni adjustment of the α-error was performed, which resulted in p = .025 as critical value for statistical significance. The comparison for sleep efficiency and memory between “Counter Strike: Global Offensive” and “Monopoly” condition was done by Wilcoxon signed rank test for repeated measures. The comparison for secondary variables (cortisol, melatonin, vigilance, other sleep variables) was also done by Wilcoxon signed rank test; the resulting p-values were not used for generalization of these results but as a measure of effect robustness instead. We calculated r-values as measures of effect sizes for all reported statistically significant tests according to Cohen who recommended Pearson r-values of .10, .30 and .50 to demarcate small, medium, and large effects [27, 28].

Results

Main questions (adjusted significance level p < .025)

For the night following the evening of “Counter Strike: Global Offensive” (CS) sleep efficiency was significantly reduced in comparison to the night following the evening of “Monopoly” (MP) (CS = 88.56% ± 7.14%; MP = 92.08% ± 2.8%; p = .017; r = .40). The recall of the fifteen words presented in the VLMT as a measurement of conscious declarative learning was worse on the morning after “Counter Strike” when participants recalled 9.56 ± 3.62 words compared to 11.83 ± 2.36 words after the “Monopoly” condition (post-sleep; p = .005; r = .46).

Additional sleep variables

The slightly lower sleep efficiency after “Counter Strike” seems to be equally due to longer sleep latency (CS = 10.93 ± 10.42 min; MP = 7.43 ± 4.91 min) and longer wake after sleep onset after “Counter Strike” (CS = 38.36 ± 24.58 min; MP = 26.25 ± 10.52 min).

Post videogaming sleep contained more light sleep stage N1 (CS = 32.17 ± 19.83 min; MP = 28.69 ± 15.73 min; p = .0497) and less sleep stage N2 (CS = 171.33 ± 30.53 min; MP = 188.24 ± 25.1 min; p = .031). There was also a small difference in the number of arousals per hour of sleep (CS = 8.85 ± 3.97; MP = 7.12 ± 2.41; p = .035).

Table 1 summarizes sleep results.

Table 1

Sleep results.

	Counter Strike: Global Offensive	Monopoly	p-value	r-value(if statistically significant)
Sleep Efficiency (%)	88.56 ± 7.14	92.08 ± 2.87	.017	.40
	90.2, 85.05; 94.4	93.3, 89.6; 94.13
Sleep Latency (min)	10.93 ± 10.42	7.43 ± 4.91	.193
	7.49, 2.88; 15.75	5.75, 3.88; 11.88
Wake after Sleep Onset (min)	38.36 ± 24.58	26.25 ± 10.52	.064
	31.68, 21; 53.25	24, 19.88; 33.82
N1-Duration (min)	32.17 ± 19.83	28.69 ± 15.73	.0497	.33
	33.25, 13.88; 49.25	28.5, 11.88; 40.25
N2-Duration (min)	171.33 ± 30.53	188.24 ± 25.1	.031	.36
	171.25, 149.13;19.13	189, 174; 214.13
N3-Duration (min)	105.72 ± 35.94	101.72 ± 29.7	.570
	100.75, 79.25; 123.25	94, 81.25; 118.75
REM-Duration (min)	72.43 ± 17.29	78.86 ± 16.35	.127
	72.87, 56.25; 84	82.5, 64.63; 92.63
Arousal- Index	8.85 ± 3.97	7.12 ± 2.41	.035	.35
	7.99, 5.49; 11.9	7.62, 4.81; 9.36

Sleep variables for “Counter Strike: Global Offensive” and “Monopoly” (mean ± SD; median; 1st quartile; 3rd quartile; relevant results marked in bold).

Free recall directly after stimulation

As we expected that interference of the more exciting videogame “Counter Strike: Global Offensive” may contribute to performance differences in declarative learning, we included a quick free recall of the previously learned 15 words directly after the stimulation on the same evening without correcting words or repeating the list. This already showed a tendency towards a worse performance in the “Counter Strike: Global Offensive” condition (Correct words pre-sleep CS = 10.56 ± 3.07; MP = 12.17 ± 2.01; p = .016; r = .40).

Vigilance and sleepiness

Self-reported acute sleepiness after the study nights (7.30 AM) did not differ between the “Counter Strike: Global Offensive” night and the “Monopoly” night (SSS-Score CS = 3.47 ± 1.00; MP = 3.33 ± 1.24; p = .816). The same applies for vigilance according to pupillography (PUI: CS = 5.85 ± 2.49; MP = 5.80 ± 2.10; p = .914). VigiMar results were also very similar for both conditions: Mean reaction time did not differ in a relevant way (CS = 2.10 ± 7.06 sec; MP = 1.94 ± 2.05 sec; p = .647). The results of the three tests are presented in Table 2.

Table 2

Vigilance results.

	Counter Strike: Global Offensive	Monopoly	p-value
SSS	3.47 ± 1.00	3.33 ± 1.24	.816
	4.00, 3.00; 4.00	3.00, 2.75; 4.00
PUI (PST, mm/min)	5.85 ± 2.49	5.80 ± 2.10	.879
	5.59, 3.73; 8.15	5.94, 4.07; 7.17
MRT (Vigimar, sec)	2.10 ± 7.06	1.94 ± 2.05	.453
	1.19, 0.80; 3.05	1.27, 0.91; 1.72

Vigilance results for “Counter Strike: Global Offensive” and “Monopoly”. SSS-Stanford Sleepiness Scale, PUI: Pupillary-Unrest-Index, MRT: Mean Reaction Time (mean ± SD; median; 1st quartile; 3rd quartile).

Melatonin

Post gaming melatonin levels between 11 PM and 12 PM close to lights out were clearly lower after “Counter Strike: Global Offensive” compared to “Monopoly” (CS = 5.74 ± 5.33 pg/ml; MP = 12.30 ± 9.80 pg/ml; p = .005; r = .47). No statistically relevant differences between both conditions were observed for other acquisition times. The pattern of melatonin level illustrated in Fig 2 indicates lower melatonin levels at lights out and nominally (but not significantly) higher values at lights on after “Counter Strike: Global Offensive”. All melatonin results are shown in Table 3.

Fig 2

Saliva melatonin levels (pg/ml) for the “Counter Strike: Global Offensive” and “Monopoly” conditions.

Table 3

Melatonin results.

	Counter Strike: Global Offensive	Monopoly	p-value	r-value(if statistically significant)
5.45 PM	1.62 ± 2.29	0.92 ± 1.01	.278
	0.95, 0.38; 1,89	0.71, 0.00; 1.29
9.07 PM	2.60 ± 2.96	2.93 ± 3.84	.836
	2.17, 0.00; 4.09	1.27, 0.62; 4.16
11.37 PM	5.74 ± 5.33	12.30 ± 9.80	.005	.47
	4.75, 0.81; 10.49	8.62, 4.12; 14.37
2.10 AM	11.50 ± 7.45	12.96 ± 7.47	.472
	10.80, 8.48; 13.85	11.54, 8.98; 13.28
7.28 AM	13.31 ± 9.99	11.28 ± 10.43	.157
	11.66, 5.05; 15.74	7.57, 4.24; 13.35

Saliva melatonin levels for “Counter Strike: Global Offensive” and “Monopoly” (pg/ml; mean ± SD; median; 1st quartile; 3rd quartile; relevant results marked in bold).

Cortisol

Cortisol values obtained while playing games (short break at 9.07 PM) showed significantly higher values during “Counter Strike” (CS = .72 ± .26 ng/ml; MP = .55 ± .21 ng/ml; p = .031; r = .36). This difference is no longer present after gaming. Cortisol values during the night and in the morning are similar for both gaming conditions. Neither the pre- nor the post-gaming cortisol level show any difference. Table 4 and Fig 3 demonstrate all cortisol values obtained.

Table 4

Cortisol results.

	Counter Strike: Global Offensive	Monopoly	p-value	r-value(if statistically significant)
5.45 PM	1.33 ± 0.89	1.45 ± 0.69	.601
	1.15, 0.85; 1.35	1.28, 0.87; 1.97
9.07 PM	0.72 ± 0.26	0.55 ± 0.21	.031	.36
	0.67, 0.55; 0.83	0.48, 0.44; 0.73
11.37 PM	0.65 ± 0.68	0.54 ± 0.29	.879
	0.50, 0.35; 0.60	0.54, 0.34; 0.67
2.10 AM	0.83 ± 0.40	0.58 ± 0.27	.081
	0.74, 0.56; 0.90	0.59,0.41; 0.78
7.28 AM	4.49 ± 1.83	4.48 ± 1.98	.948
	3.92, 3.29; 5.62	3.84, 3.17; 5.82

Saliva cortisol levels for “Counter Strike: Global Offensive” and “Monopoly” (ng/ml; mean ± SD; median; 1st quartile; 3rd quartile; relevant results marked in bold).

Fig 3

Saliva cortisol levels (ng/ml) for the “Counter Strike: Global Offensive” and “Monopoly” conditions.

Discussion

Discussion of methods

Most studies about video gaming and sleep had relatively low sample sizes. Higuchi et al. had seven PSG recordings, Weaver et al. nine and Dworak et al. ten recordings [12, 13, 29]. King et al. had objective sleep data from seventeen subjects which is close to our sample size of eighteen participants [14]. Compared to the existing studies, our sample size is rather high. Furthermore, taking night to night variability in sleep studies into account, even larger sample sizes are desirable. As videogaming is more prevalent in male adolescents we decided to include only male subjects [7]. This homogeneity leads to a better relation between effect-variability and between-subjects-variability. Of course, this means that our results should only be generalized for male subjects. We chose long gaming durations of 300 minutes for each condition which is long compared to other studies (60 min Dworak et al. [29]; 50 min Weaver et al. [12]; 165 min Higuchi et al. [13]. However, on average, male German adolescents play videogames for more than 160 minutes on weekend days [7]. For weekdays, 5.5% of male adolescents report playing videogames for 300 minutes or more and on weekends, this proportion rises to 15.9%. In addition, total daily usage time of electronic media for German adolescents is greater than five hours per day [30]. So 300 minutes gaming time seems long, but is definitely not beyond daily routine experience of male adolescents. Accordingly, not a single study participant found 5 hours of “Counter Strike” unusual or too long, while several complained about five hours of playing “Monopoly” being too long. Another reason for the long gaming time was our intent to maximize potential effects in our small sample. This experimental design compares an exciting computer game with the rather boring board game “Monopoly”. For a better comparability a more fast-paced board game could have been used. Many sleep studies use a standardized time in bed of eight hours. We chose a shorter time in bed of seven hours. A large scale study with 5275 German adolescent subjects [31] showed an average 6 h 47 min reported weekday time in bed, so our time in bed is close to the time spent in bed in real life. Due to a tight schedule in the sleep laboratory and the duration of playing five hours the games in teams, it was not possible to adjust the bed/wake times to the habitual sleep times. In comparison to the given time in bed of our participants (7,65±0,57 hours during the week and 9,02±1,26 hours at the weekend), seven hours are quite short. Different bed times could influence the outcome of the sleep measurements.

Discussion of results

We found a negative effect of playing “Counter Strike” on both our main variables. Sleep efficiency was slightly but significantly reduced by 3.5% after prolonged playing “Counter Strike” compared to the same duration of playing Monopoly. This translates to fifteen more minutes spent in wakefulness during time in bed. King et al. also found lowered sleep efficiency after prolonged videogaming, whereas other authors found no effect on sleep efficiency [13, 14, 29]. Recall after declarative learning was reduced on the morning after playing “Counter Strike” compared to the “Monopoly” condition. Bad sleep [32] as well as interference between learning and retention [17, 33] can impair memory function. In post hoc analysis of the remembered words directly after the stimulation (pre-sleep), we already found a tendency of the declarative memory performance being worse after playing “Counter Strike” (p = .031). This difference gets more robust after the consolidation during the night at the next morning free recall (p = .005). All statistically significant results fall into the medium effect size range (r = .30 - .50) according to Cohen [27,28]. With our sample size and study design it is not feasible to measure the exact contributions of the two expected main effects on declarative learning: interference and consolidation. Most likely both contribute to memory performance being worse in the morning after playing “Counter Strike”, the parameter we considered most relevant as it shows what our subjects actually remembered. In recent papers about memory encoding it was stated that a rise in cortisol levels can facilitate recall of learned information, but only if the hormone levels are high in pre-learning stage [20] and low during encoding and consolidation [18]. In comparison of “Counter Strike” and “Monopoly” we saw significantly rising cortisol levels after the learning phase (during the game) and again elevated cortisol levels in the sleep stage (not significant). This could have led to more interference of the impressions during the game with the previously learned words, as the new impressions were likely “tagged” as more important because of higher stress levels [20], and less effective consolidation in sleep [18]. Following this hypothesis, maybe it would have made more sense to play “Counter Strike” before learning and go to sleep after learning. This could be an interesting subject for further studies. Relating to additional results, more time spent in N1 and a slightly higher arousal-index can be viewed as indicators for lighter sleep after “Counter Strike”. In line with these sleep results Melatonin values after gaming and before bedtime were lower in the videogame condition. Ivarsson et al. did not find increased arousals after violent videogames compared to non-violent games, but they described more awakenings in frequently videogaming adolescents compared to adolescents who scarcely used videogames [34, 35]. Higuchi et al. found lowered REM sleep after videogaming [13]. While we also observed seven minutes less of REM sleep after “Counter Strike”, this difference failed to reach statistical significance in our study. This might partially be due to our short time in bed of seven hours which curtailed sleep at the end of the resting period, the time when REM is more probable than in the first half of the night. Prolonged evening videogaming of “Counter Strike: Global Offensive” seems to impair melatonin secretion as indicated by significantly lower melatonin levels at bedtime. Higher light exposure during “Counter Strike” (50 lux vs. 20 lux during “Monopoly” what is quite dim) with constant observation of a bright computer monitor can cause this effect. Several studies have shown that light from a computer monitor is sufficient to reduce and phase-delay melatonin secretion [5, 36]. Accordingly, our data indicates lower melatonin levels at bedtime and higher absolute melatonin levels in the morning (not significant) after “Counter Strike”, while maximum levels at 2 AM are similar for both conditions. Excitation from video gaming can contribute to this effect. Excitement and tension can cause pupil dilatation via sympathetic arousal [37], which increases sensitivity to light and reduces melatonin secretion [38]. We are aware of one other study which addresses melatonin levels and videogaming. Higuchi et al. demonstrated significantly reduced melatonin levels after playing exciting videogames in front of bright computer screens [39]. Solving non-exciting tasks presented on screens with similar brightness did not impair melatonin secretion. These results also indicate an interaction between light and excitement. Eyes with wide pupils are more sensitive to light which increases the risk for reduced melatonin production [38]. Several studies found no increases in stress hormone cortisol levels for pre-post videogaming comparisons [16, 34]. These findings are in line with our results for the pre-post comparison and frequently lead to the conclusion that even violent videogaming compared to no gaming at all does not increase cortisol secretion [34]. In contrast to existing studies we took cortisol samples in a short break in the middle of the videogaming period. In agreement with the well-known circadian evening decline in cortisol [40], we found lower cortisol levels during both gaming periods than before gaming started. But mid-gaming cortisol levels during “Counter Strike” were significantly higher than those observed during “Monopoly”. So, our results indicate slightly higher levels of the stress hormone cortisol during the exciting video game “Counter Strike”. In agreement with hints for slightly impaired sleep after the violent videogame “Counter Strike” we found a trend towards slightly higher cortisol levels during the nocturnal resting period. Sleepiness and vigilance testing results did not differ for both gaming conditions. This is not surprising as the observed effects on sleep after one evening of prolonged playing the violent videogame “Counter Strike” were small and not clinically meaningful. Nevertheless, there is data indicating that adolescents with habitual high levels of electronic media use are sleepier [41]. The lack of effect in this area is probably due to the single stimulus used in this study. Repeated exposure to prolonged gaming might yield clearer results.

Conclusion

Prolonged playing the video game “Counter Strike: Global Offensive” seems to impair sleep and declarative memory. We consider these medium sized effects remarkable as they occur after different leisure activities and not after formal interventions directly aimed at sleep or memory. Future studies should aim to disentangle the effects of nocturnal light and inherent excitement and engagement associated to violent video gaming from each other. It may also be interesting for future studies to find out to which extent observed declarative memory performance differences are caused by interference after learning in contrast to consolidation during sleep. In addition to that an exciting video game as “Counter Strike: Global Offensive” is compared to the rather boring board game “Monopoly”. Future studies could compare an exciting video game to an also more exciting board game.

Data availability.

(XLSX)

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24 Jul 2019

PONE-D-19-17611

The effects of prolonged videogaming on sleep and declarative memory

PLOS ONE

Dear Mrs. Hartmann,

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.

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I agree that the manuscript presents an interesting research and deserves consideration, given that adequate revision will be provided by Authors basing on Reviewers' concerns.

In particular, I agree that the manuscript's tone should be softened at times, basing on what it has actually been done. Possibly the main limitation of the study is the usage of Monopoli, while Authors could easily find some fast-paced, stressful, combat-themed board game allowing for more proper comparison. I suggest Authors to (1) add a more specific limitations section with this and other limitations identified by Reviewers explicitly stated, and (2), when referring to the experiment (text, tables, figures included), to not report the comparison between "video gaming and board gaming", but between "counter strike and monopoli", as these products are not necessarily representative of all the extremely rich gaming scenario.

About this: the two games used should be described in more detail, given that they are the only experimental operators.

Future research section could be improved as well, taking into account that comparison beetween different board/video games could potentially lead to opposite results.

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Reviewers' comments:

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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

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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

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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: Dear authors,The paper needs further investigation.

1 - You used a violent video game (Global strike - Global Offensive) and a board game (Monopoly). Why didn't you use other kinds of video games? Video game is very activating (see Kovess-Masfety et al (2016). Is time spent playing video games associated with mental health, cognitive and social skills in young children?). While the board game is less activating (the arousal of the BN is lower) and consequently you have received more complaints about 5 hs of playing a board game being too long. It is considered a boring activity, obviously sleep arises first.

2 - Why did the subjects participate in both experimental conditions? In this way it was possible to create an expectation effect.

3 – In “Procedure” you say that “50% of the participants played the board game on the second weekend and the video game in the third weekend, the other half played in reverse sequence”. Have you analyzed if the different sequences (VN-BN and BN-VN) gives different effects on variables? Compare the results of variable in the two groups that followed different sequences.

4 - It is true that 300 minutes of playing video games are many, but the exposure is only one. Specify in the paper that the effects occur following a short-term exposure. The title could be changed to "The effects of prolonged single night session of videogaming on sleep and declarative memory"

5 – In the first phrase of the paragraph “Discussion of Results”, word “detrimental” is too strong. Replace with a more suitable term.

6 – Which Correct Words value is reported in the paper? Pre- or Post- sleep? This is unclear.

7 - Why didn't you use a non-verbal declarative memory test? For example a visual declarative memory test. Other information could emerge (see Peracchia, S., & Curcio, G. (2018). Exposure to video games: effects on sleep and on post-sleep cognitive abilities. A sistematic review of experimental evidences)

8 - Update the literature.

Reviewer #2: The experiment presented by Hartmann et al. investigates the effect of prolonged evening usage of videogames on declarative memory and sleep. They find that sleep efficiency and declarative memory performance were both significantly reduced and speculate that these findings may be due to increased interference and impaired overnight consolidation in the videogame condition, although they are unable to fully disentangle the two.

Since increased screen time and gaming are both increasingly prevalent in modern society, this is a relevant research question and the results are suitable for publication in PLOS One. My concerns rest primarily with the lack of detail in the methodology, specifically:

1. How was the VLMT administered? The text states that the list was memorized through five repetitions, but do not state whether words were presented one at a time, all together, etc., how much time participants were given to study the list, how much time passed in between repetitions, whether it was a computerized task, etc. Nor do the authors mention how much time participants were given for the free recall of the word list. It is not clear what is meant by “the recall was preannounced in each repetition” –does this mean participants were explicitly instructed to memorize the words?

2. For the 5 hours of gaming, were participants gaming continuously without breaks (other than the scheduled break at 8:55 to collect saliva)? It is also unclear whether the PCs were the sole source of light while playing video games or if there was additional ambient room lighting. Was the 20 lux of ambient lighting during the board game also measured at eye level? I am also curious how 20 lux was selected for the ambient lighting during the board game, as it is quite dim compared to ordinary room lighting. Finally, what lux was the room during the sleep period?

3. Were habitual bed/wake times taken into account during screening? Especially because sleep is one of the primary outcome measures, it is important to note whether the lab-scheduled sleep opportunities are at similar times to the participants’ habitual sleep times. If participants are attempting to sleep at times very different from their normal time, their sleep may be impacted independent of gaming condition.

4. How was the timing of the saliva samples chosen? Also, it would be helpful to report the average time and standard deviation of the fourth nocturnal saliva sample, so that readers are aware of the variability of this sample time.

5. Why was the VigiMar test used to assess vigilance instead of the more commonly used Psychomotor Vigilance Test (PVT)? And given that the VigiMar is a very long test, were there any differences in time-on-task effects in the two conditions?

6. The authors report significantly lower melatonin levels after video gaming compared to board games (pg 10) and state that this “indicates a phase delay of melatonin secretion”. While this clearly indicates melatonin suppression, and it is possible that evening video games could have caused a phase delay, the current experimental design does not allow them to assess whether there has actually been a phase shift. Similar on pg 14, line 360, the data show melatonin suppression but not necessarily a phase delay.

7. Although the authors note that participants were scheduled to 7 hours time in bed, which is close to the average for German adolescents, they also report on page 5 that their participants reported sleeping on average 7.65 hrs in bed during the week and 9.02 hrs on the weekend. Thus, it is likely that they were either somewhat sleep restricting the participants, or at the very least scheduling wake times significantly different from the participants’ habitual wake. This should be mentioned in the discussion of scheduled time in bed.

8. Minor typographical errors in the text:

a. Use consistent tense throughout the manuscript. E.g. on pg 2, line 28, change “does” to “did”; pg 14 line 355, change “seems” to “seemed”, etc.

b. Pg 5 in the ethics statement, it is not clear what “All participants were tired and informed…” is intended to say.

c. Pg 6, line 172 “brake” should be changed to “break”

d. Pg 15, line 393 “extend” should be changed to “extent”

**********

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Reviewer #1: No

Reviewer #2: No

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Submitted filename: Rewiev PONE.pdf

Click here for additional data file.

6 Sep 2019

Reviewer 1:

1) You used a violent video game (Global strike - Global Offensive) and a board game (Monopoly). Why didn't you use other kinds of video games? Video game is very activating (see Kovess-Masfety et al (2016). Is time spent playing video games associated with mental health, cognitive and social skills in young children?). While the board game is less activating (the arousal of the BN is lower) and consequently you have received more complaints about 5 hs of playing a board game being too long. It is considered a boring activity, obviously sleep arises first.

Response: "Counter Strike: Global Offensive" is one of the most popular video games among adolescents and all of our participants had at least some experience with the game. We used this violent video game because of its high topicality, the possibility of team playing including fighting against each other. In our small sample, we wanted to maximize potential effects by playing a violent game for a very long time (five hours). Since 2018, after our study measurements, the video game "Fortnite" has become the most popular video game among 12 – 19 years old German adolescents (Medienpädagogischer Forschungsverbund Südwest. JIM 2018 Jugend, Information, (Multi-)Media: Basisstudie zum Medienumgang 12- bis 19-Jähriger in Deutschland 2018). Nowadays this game could be an alternative video game condition.

In line with the Academic Editor Mr. Triberti we added a paragraph about the comparison of the rather boring “Monopoly” and the more exciting computer game (l. 320-322; l. 412-415). In general, we consciously intermingled the aspect “exciting” with video gaming and “less exciting” with board gaming because we wanted to maximize effects. The drawback that inevitably goes along with that decision has been emphasized in the new version of the manuscript. Another not so scientific reason for choosing monopoly were the reports of the more senior co-authors (Koehler, Cassel) that they had spent considerable time with playing Monopoly as adolescents.

2) Why did the subjects participate in both experimental conditions? In this way it was possible to create an expectation effect.

Response: The first weekend was just a habituation phase with no gaming conditions. The adolescents participated in a reverse sequence model so 50 % played "Counter Strike: Global Offensive" at the second weekend and "Monopoly" at the third weekend. The other 50 % played "Monopoly" first and then "Counter Strike: Global Offensive". Interindividual sleep can vary widely. With our small sample size of 20 (including two drop outs) participants we wanted to prevent a high interindividual variation. While independent samples would have avoided the expectation effect, they would have introduced more interindividual variations requiring larger sample sizes which would have been very difficult to achieve.

3) In “Procedure” you say that “50% of the participants played the board game on the second weekend and the video game in the third weekend, the other half played in reverse sequence”. Have you analyzed if the different sequences (VN-BN and BN-VN) gives different effects on variables? Compare the results of variable in the two groups that followed different sequences.

Response: Thank you for this suggestion. We have compared the results in the two different groups. Sequence 1: Counter Strike - Monopoly; Sequence 2: Monopoly - Counter Strike. Unfortunately, the two drop outs of the study were both in the sequence 2 group, so there are just eight data sets in sequence 2 and ten data sets in sequence1 (l. 168-172 in the manuscript).

There was a sequence effect in the following variables (CS=VN, MP=BN):

Sleep variables:

N1-Duration MP: Seq 1 = 35,35 ±13,09; Seq 2 = 20,38 ± 15,42; p = .034

N3-Duration CS: Seq 1 = 90,85 ± 32,38; Seq 2 = 124,32 ± 32,82; p = .027

Pupillographic sleepiness test:

PUI CS: Seq 1: 4,45 ± 1,97; Seq 2: 7,59 ± 1,95; p = .004

VigiMar:

MRT CS: Seq 1: 1,17 ± 0,62; Seq 2: 3,24 ± 2,34; p = .027

Cortisol:

Cortisol 11.37 PM MP: Seq 1: 0,69 ± 0,25; Seq 2: 0,35 ± 0,20; p = .003

Cortisol 02.10 AM MP: Seq 1 0,69 ± 0,14; Seq 2: 0,44 ± 0,33; p = .016

(Extract of our excel list. Please have a look at our document "Response to the reviewers")

To sum up, we can identify the following points:

1. Those who played Counter Strike in the first night

- had less deep sleep after the videogame but more light sleep after Monopoly

- were more alert on the next morning after Counter Strike during the VigiMar and PST

Despite of the first habituation night, the combination of Counter Strike and the first night with measurements could have been more exciting than Monopoly and measurements.

2. Those who played Counter Strike in the first night

- had higher cortisol levels directly after and in the night after Monopoly

Perhaps the adolescents were more annoyed of the board game. They have already played the more entertaining computer game on the other weekend. In regards to the group structure of four or five adolescents they were glad and excited that the measurements come to an end so they pushed each other for the last time.

Admittedly, these findings and interpretations are rather vague so we did not include them into the manuscript. We think they would rather distract the reader than give additional good structured information.

4) It is true that 300 minutes of playing video games are many, but the exposure is only one. Specify in the paper that the effects occur following a short-term exposure. The title could be changed to "The effects of prolonged single night session of videogaming on sleep and declarative memory"

Response: That is an excellent point. Thank you! We changed the title as suggested.

5) In the first phrase of the paragraph “Discussion of Results”, word “detrimental” is too strong. Replace with a more suitable term.

Response: We replaced the word with "negative".

6) Which Correct Words value is reported in the paper? Pre- or Post- sleep? This is unclear.

Response: We are sorry that this point is not clear. It depends on different parts in the paper. One of our main questions was if there is a difference in declarative memory between "Counter Strike" and "Monopoly" on the next morning, so this means post-sleep (results in l. 228-231)

In addition, we compared differences in declarative memory performance directly after the "Counter Strike"/ "Monopoly" stimulation, so this means pre-sleep (results in l. 246-252). We added "pre- and post-sleep" in some parts of the paper (l. 251; l. 341; l. 115; l. 231)

7) Why didn't you use a non-verbal declarative memory test? For example a visual declarative memory test. Other information could emerge (see Peracchia, S., & Curcio, G. (2018). Exposure to video games: effects on sleep and on post-sleep cognitive abilities. A sistematic review of experimental evidences)

Response: The most important point for the decision for the memory test was the possibility for repeating testing. The VLMT has got three comparable versions for every night. A non-verbal test could be a good alternative but it was a conscious decision to choose a verbal test because we did not want to use a screen at the board game night.

8) Update the literature.

Response: We updated and checked the literature. Thank you for your suggestions.

Reviewer 2:

1) How was the VLMT administered? The text states that the list was memorized through five repetitions, but do not state whether words were presented one at a time, all together, etc., how much time participants were given to study the list, how much time passed in between repetitions, whether it was a computerized task, etc. Nor do the authors mention how much time participants were given for the free recall of the word list. It is not clear what is meant by “the recall was preannounced in each repetition” –does this mean participants were explicitly instructed to memorize the words?

Response: Sorry, this is not described clearly in the paper. Every participant knew that he would have to repeat the words.

The investigator read out all 15 words, then the participant had to reproduce all the memorized words. After that, the investigator read out all the words again and the participants repeated. In sum this happened five times. Afterwards a different list of 15 words was read out and the participant had to repeat them. Then they played Counter Strike or Monopoly. After the game (pre-sleep) there was another recall without a repetition of the words. On the next morning (post-sleep) the participants had to repeat the words again without a preceding repetition. There was no exact time limit for the recall but after approximately a minute the recall was stopped.

We added more information about the VLMT in the methods (l. 151-158).

2) For the 5 hours of gaming, were participants gaming continuously without breaks (other than the scheduled break at 8:55 to collect saliva)? It is also unclear whether the PCs were the sole source of light while playing video games or if there was additional ambient room lighting. Was the 20 lux of ambient lighting during the board game also measured at eye level? I am also curious how 20 lux was selected for the ambient lighting during the board game, as it is quite dim compared to ordinary room lighting. Finally, what lux was the room during the sleep period?

Response: There were no additional breaks during the stimulation. In fact, the participants were offered some food and drinks but they were told to play while eating.

There was additional room light while playing video games and the light intensity was measured at eye level in both conditions. The eye-screen-distance was about 30 cm. We chose a more ambient light during the board game because we wanted to reproduce a quiet board game evening at home like it may have typically happened 40 years ago. We added more information about that in the new version of the manuscript (l. 176; l. 373).

3) Were habitual bed/wake times taken into account during screening? Especially because sleep is one of the primary outcome measures, it is important to note whether the lab-scheduled sleep opportunities are at similar times to the participants’ habitual sleep times. If participants are attempting to sleep at times very different from their normal time, their sleep may be impacted independent of gaming condition.

Response: Unfortunately, there has been no adjustment of the personal habitual bed/wake times. Every night had a tight schedule in the sleep laboratory. The participants played the games for five hours together so it was not possible to create a timetable referring to everybody’s bed times. But you are definitely right. We added this topic to the discussion part (l. 326-330).

4) How was the timing of the saliva samples chosen? Also, it would be helpful to report the average time and standard deviation of the fourth nocturnal saliva sample, so that readers are aware of the variability of this sample time.

Response: The aim of the saliva samples was to show the time course of the two hormones. The samples were taken before, in the middle and at the end of the game. To see the progression, the fourth samples was taken in the night. The extraction should cause the least possible disturbance so a time was chosen when less REM or slow wave sleep was expected (having in mind that the typical sleep cycle lasts 70-100 minutes). The mean and standard deviation of the fourth saliva sample time is 02.10 AM ± 19 minutes. We added this to the paper. The paper was not submitted with the actual version of table 3 and 4. We are sorry for that and changed it. In a former version, there was a little excel fault with regard to the sample times.

5) Why was the VigiMar test used to assess vigilance instead of the more commonly used Psychomotor Vigilance Test (PVT)? And given that the VigiMar is a very long test, were there any differences in time-on-task effects in the two conditions?

Response: The VigiMar was developed in Marburg where the study was conducted. The employees of the sleep laboratory know the test very well so it was easy to use it. In addition to that, we wanted to investigate a long-term vigilance test. The VigiMar is frequently used in Germany and described in a standard textbook of the German Sleep Society about methods in sleep medicine (Kompendium Schlafmedizin).

We haven´t included any data about the time-on-task effect into our data set yet so at this point we cannot compare this effect in the two conditions. Generally, it´s possible to adopt additional information into our digital data set but therefore another analysis of our analogue raw data set is necessary. In effect, it means that we have to go back to paper source data and to check it with our quality assurance as we´ve done with the rest of our data. For this process more time would be needed. Until now, we haven´t paid special attention to the time-on-task effect because we thought it would be rather slight but generally an analysis could be supplemented if a future revision is required.

6) The authors report significantly lower melatonin levels after video gaming compared to board games (pg 10) and state that this “indicates a phase delay of melatonin secretion”. While this clearly indicates melatonin suppression, and it is possible that evening video games could have caused a phase delay, the current experimental design does not allow them to assess whether there has actually been a phase shift. Similar on pg 14, line 360, the data show melatonin suppression but not necessarily a phase delay.

Response: You are right that the design does not allow to state a phase delay. We modified the wording accordingly (l. 272; l. 377).

7) Although the authors note that participants were scheduled to 7 hours time in bed, which is close to the average for German adolescents, they also report on page 5 that their participants reported sleeping on average 7.65 hrs in bed during the week and 9.02 hrs on the weekend. Thus, it is likely that they were either somewhat sleep restricting the participants, or at the very least scheduling wake times significantly different from the participants’ habitual wake. This should be mentioned in the discussion of scheduled time in bed.

Response: This is a limitation of the experimental design and has been added to the discussion of the methods (l. 326-330).

8) Minor typographical errors in the text:

a. Use consistent tense throughout the manuscript. E.g. on pg 2, line 28, change “does” to “did”; pg 14 line 355, change “seems” to “seemed”, etc.

b. Pg 5 in the ethics statement, it is not clear what “All participants were tired and informed…” is intended to say.

c. Pg 6, line 172 “brake” should be changed to “break”

d. Pg 15, line 393 “extend” should be changed to “extent”

Response: Thank you for your excellent and very thorough review. We have corrected the errors.

Submitted filename: Response to Reviewers06.09.2019.docx

Click here for additional data file.

24 Sep 2019

PONE-D-19-17611R1

The effects of prolonged single night session of videogaming on sleep and declarative memory

PLOS ONE

Dear Mrs. Hartmann,

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.

==============================

First of all I am Dr., not Mr.

Reviewers have re-evaluated the manuscript and Reviewer 2 identified further modifications to be included.

Moreover, it had been asked according to journal requirements to add effect sizes, especially because the effect is deemed "surprisingly large" in conclusion. I was not able to find the effect sizes at the lines and tables Authors report in the response, but only means and p values. These should be added. I also suggest to modify those lines in conclusion; first, they seem unnecessary to comment on Authors' results, second they would be inappropriate unless the effect size is extremely high taking into consideration previous literature on the topic.

==============================

We would appreciate receiving your revised manuscript by Nov 08 2019 11:59PM. When you are 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.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

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). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.

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Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Stefano Triberti, Ph.D.

Academic Editor

PLOS ONE

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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: All comments have been addressed

Reviewer #2: (No Response)

**********

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: Dear authors

I am very happy that you have made the suggested changes.

The study now appears clearer and more complete, suitable for publication.

On careful reading, the manuscript appears complete in all its parts.

It's technically valid and supports the conclusions.

Reviewer #2: I appreciate the opportunity to review the revised manuscript, and thank the authors for addressing the comments. My only remaining concern is that the revised description of the VLMT is still somewhat unclear. If the VLMT has been published previously, perhaps the authors could include a citation/reference with a more detailed description of the task? The parts I still found confusing are as follows:

Pg 6, L155 “…this list was read out by the investigator and reproduced by the participants for five times each”

It is unclear to me whether this means participants are verbally repeating the words as the investigator reads each word aloud, or if participants are being asked to repeat the full list from memory after the investigator has finished reading all 15 words, etc. From the comments to the reviewers, it sounds as though participants are being asked to freely recall all 15 words immediately after the investigator reads the full list, in which case it would be important to report whether participants received any feedback if they made errors or prompting if they were unable to successfully repeat all 15 words. The information about recall time should also be reported in the text.

Pg 6, L156-57 “…then another list with fifteen words was read to the participants who had to reproduce them”

Please clarify the purpose of this second list of words-- is it for masking/interference, or are participants tested on this list as well?

Again, I appreciate the authors’ work in addressing the reviewer comments in the discussion. I believe the manuscript is ready for publication with minor revisions to improve clarity.

**********

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: Yes: Peracchia Sara

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 to be viewed.]

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18 Oct 2019

Dear Dr. Triberti, Dr. Peracchia and Reviewer 2,

Thank you for your reviews and the chance to revise the manuscript for a second time. First of all, please accept our sincere apologies for addressing you as Mr instead of the correct form Dr. In the following text we respond to your suggestions point-by-point again.

Dr. Stefano Triberti:

1) Moreover, it had been asked according to journal requirements to add effect sizes, especially because the effect is deemed "surprisingly large" in conclusion. I was not able to find the effect sizes at the lines and tables Authors report in the response, but only means and p values. These should be added. I also suggest to modify those lines in conclusion; first, they seem unnecessary to comment on Authors' results, second they would be inappropriate unless the effect size is extremely high taking into consideration previous literature on the topic.

Unfortunately, we have misunderstood your last suggestion for the first revision. You are right that no measures of effect sizes have been shown until now. We have calculated effect sizes for all statistically significant tests. We have added these to the tables and changed the text of the manuscript (i.e. l. 222-224, l. 235, l. 348-349, l. 412-414)

According to Cohen, all the reported r-values show a medium effect size for the statistically significant tests (r-values of 0.10, 0.30, and 0.50 to demarcate small, medium and large effects). Recent studies remark that Cohen's correlation guidelines are too exigent. They suggest to consider correlations of 0.10, 0.20 and 0.30 as relatively small, typical (medium) and relatively large for individual differences researchers. According to Gignac, our results show a large effect. (Gignac, Gilles E.; Szodorai, Eva T. (2016): Effect size guidelines for individual differences researchers. In: Personality and Individual Differences 102, S. 74–78. DOI: 10.1016/j.paid.2016.06.069.)

In our manuscript we used the established and rather conservative evaluation of Cohen's guidelines.

Dr. Sara Peracchia:

Thank you very much for your well composed review. We appreciate your positive decision.

Reviewer 2:

1) I appreciate the opportunity to review the revised manuscript, and thank the authors for addressing the comments. My only remaining concern is that the revised description of the VLMT is still somewhat unclear. If the VLMT has been published previously, perhaps the authors could include a citation/reference with a more detailed description of the task? The parts I still found confusing are as follows:

Pg 6, L155 “…this list was read out by the investigator and reproduced by the participants for five times each”

It is unclear to me whether this means participants are verbally repeating the words as the investigator reads each word aloud, or if participants are being asked to repeat the full list from memory after the investigator has finished reading all 15 words, etc. From the comments to the reviewers, it sounds as though participants are being asked to freely recall all 15 words immediately after the investigator reads the full list, in which case it would be important to report whether participants received any feedback if they made errors or prompting if they were unable to successfully repeat all 15 words. The information about recall time should also be reported in the text.

Pg 6, L156-57 “…then another list with fifteen words was read to the participants who had to reproduce them”

Please clarify the purpose of this second list of words-- is it for masking/interference, or are participants tested on this list as well?

We are really sorry that this part is still unclear. The participants were asked to recall the words after the investigator has finished reading all 15 words. The second list was just a distractor list. They were tested on this list as well, but only in one immediate recall which is not reported in the manuscript.

We have changed the description of the VLMT in the manuscript. Hopefully it is more understandable now:

“The VLMT consists of two lists, each with fifteen unrelated words (list A and list B). There is a parallel form for repeated testing. List A is read out by the investigator in five consecutive learning trials, each followed by an immediate free recall by the participants. This is followed by one round of reading and immediate recall of the distractor list. After the “Counter Strike: Global Offensive” resp. “Monopoly” stimulation (pre-sleep) and on Sunday morning (post-sleep) the participants were asked to recall the words from list A. There was no exact time limit for the recall, but it usually lasted less than one minute until subjects stated that they recalled no further words. There was no feedback about the number of correct recalled words.”

The VLMT represents a modified German version of the Rey Auditory Verbal Learning and Memory Test (RAVLT).

A version of the test has been published by Witt for example (Witt, JA., Coras, R., Becker, A.J. et al. Brain Struct Funct (2019) 224: 1599. https://doi.org/10.1007/s00429-019-01857-1).

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24 Oct 2019

The effects of prolonged single night session of videogaming on sleep and declarative memory

PONE-D-19-17611R2

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Reviewers' comments:

5 Nov 2019

PONE-D-19-17611R2

The effects of prolonged single night session of videogaming on sleep and declarative memory

Dear Dr. Hartmann:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

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