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The power of children’s sleep - Improved declarative memory consolidation in children compared with adults


Abstract and Figures

Post-learning slow wave sleep (SWS) is known to support declarative memory consolidation. As SWS is more abundant in young population, we suggested that sleep-dependent memory consolidation processes could occur at a faster pace in school-aged children. After learning new associations between non-objects and their functions, retrieval performance was tested in 30 children (7–12 years) and 34 adults (20–30 years) during an immediate (IR) and a delayed retrieval (DR) session separated by either a Sleep or a Wake condition. Sleep led to stabilized memory retrieval performance only in children, not in adults, whereas no age-related difference was observed after a similar period of wakefulness. Hence, our results suggest more efficient sleep-dependent declarative memory consolidation processes in children compared with adults, an effect potentially ascribed to more abundant and deeper SWS during childhood.
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The power of children’s sleep -
Improved declarative memory
consolidation in children compared
with adults
Anna Peier1,2 ✉ , Maud Brichet1,2, Xavier De Tiège1, Philippe Peigneux2 & Charline Urbain1,2 ✉
Post-learning slow wave sleep (SWS) is known to support declarative memory consolidation. As SWS
is more abundant in young population, we suggested that sleep-dependent memory consolidation
processes could occur at a faster pace in school-aged children. After learning new associations between
non-objects and their functions, retrieval performance was tested in 30 children (7–12 years) and 34
adults (20–30 years) during an immediate (IR) and a delayed retrieval (DR) session separated by either
a Sleep or a Wake condition. Sleep led to stabilized memory retrieval performance only in children, not
in adults, whereas no age-related dierence was observed after a similar period of wakefulness. Hence,
our results suggest more ecient sleep-dependent declarative memory consolidation processes in
children compared with adults, an eect potentially ascribed to more abundant and deeper SWS during
Children, particularly at school-age, have to learn and consolidate high quantities of new declarative informa-
tion (e.g. learning a vocabulary list in a foreign language) to respond adequately to environmental demands.
According to system consolidation theories, declarative knowledgeis progressively integrated into long-term
memory through brain plasticity processes generating functional and structural changes at the neural level1,2.
Both in adults38 and across development9, studies showed that sleep plays an active role in these plasticity-related
changes promoting memory consolidation processes. In particular, slow wave sleep (SWS) has been suggested
to trigger (i.e. elicit) the transfer of newly learned representations, initially stored in the hippocampal and
para-hippocampal areas, towards prefrontal brain areas for long term storage8,1012. Childhood, compared with
adulthood, is not only characterized by a higher amount and variety of learning experiences supported by cere-
bral plasticity processes13,14 but also by a higher amount of SWS1518. Compelling evidence suggests that children
(7–12 years old) spend signicantly longer proportion of their night sleep time in SWS (around 25 to 35%)
than adults (around 15 to 20%)15,1821. As several studies suggested that SWS markedly contributes to declarative
memory consolidation processes across development and as SWS is more abundant in school-age children than
adults, it has been suggested that sleep-dependent memory consolidation processes may be more ecient and/or
accelerated in children than in adults22,23. In line with this proposal, it has been shown using magnetoencephalog-
raphy (MEG) that in 7–11 year old children, a 90-minute daytime nap is already sucient to trigger changes in
signal amplitude of the neural substrates related to the long-term storage of newly learned declarative material23.
Importantly, a similar brain reorganization associated with the course of memory consolidation was previously
observed in adults, but only days to months aer the initial learning session8,12.
At the behavioural level, the beneficial impact of sleep on declarative memory consolidation has been
observed in adults3,5,8,22,24, children22,2527, and adolescents28 either through stabilized or improved memory reten-
tion performance at delayed recall (compared with immediate recall). Yet, to the best of our knowledge, only
three studies have compared the impact of sleep on memory consolidation performance between children and
adults22,29,30 and did not highlight a developmental advantage of sleep on memory consolidation performance.
For instance, Wilhelm et al. (2008)22 compared sleep-dependent declarative memory consolidation performance
1Laboratoire de Cartographie fonctionnelle du Cerveau (LCFC), UNI – ULB Neuroscience Institute, Université libre
de Bruxelles (ULB), Brussels, Belgium. 2Neuropsychology and Functional Imaging Research Group (UR2NF), Center
for Research in Cognition and Neurosciences (CRCN), UNI – ULB Neuroscience Institute, Université libre de Bruxelles
(ULB), Brussels, Belgium. e-mail: anna.pei;
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between children aged 6–8 years and adults, using a classical word-pair associate learning task. Participants had
a better recall performance aer a night of sleep compared to a similar period of wakefulness. However, over-
night improvements in performance were similar between adults and children, despite a twice as large amount
of SWS in children than in adults during the post-training sleep period. Since pre-existing knowledge boosts
memory consolidation processes3133, the authors explained this lack of eect by the imbalance of pre-existing
representations associated with the learning material between children and adults. Smaller amount of schemata
and knowledge associated to the newly learned material (i.e., word pairs) in children may have prevented observ-
ing a potential advantage of sleep on memory consolidation performance in the younger population compared
with adults22,34.
In this framework, the present study investigated the potential age-related advantage of sleep on declarative
memory consolidation performance using a learning task that allows a clear comparison between children and
adults, by minimizing the impact of pre-existing representations on the to-be-learned material. To do so, we
explored the impact of sleep on the consolidation of new associations between non-objects and their “magical”
function, a material that is equally novel for adults and children23,35. We hypothesize that aer controlling for the
impact of pre-existing representations, children (7–12 years) would exhibit larger gains in memory retention
performance (i.e., dierence between the number of correctly recalled items at the delayed vs. the immediate
retrieval sessions) than adults (20–30 years) over a night of sleep.
Sleep and circadian parameters. Sleep parameters are reported in Table1.
Sleep duration did not dier between the Sleep and Wake groups (see Methods section) during the nights
preceding the experiment (Night-2, Sleep: 9.93 ± 1.25 vs. Wake: 10.03 ± 0.88 h; Night-1, Sleep: 10.12 ± 1.37 vs.
Wake: 10.38 ± 1.21 h), either in the children (all ps > 0.18) or in the adult (all ps > 0.25) g roups.
In children, the average sleep duration for the two nights preceding the experiment did not dier from their
average sleep time over the past month (N-2: mean ± SD 10.0 ± 1.1 h, p = 0.5; N-1: 10.2 ± 1.3 h, p = 0.015).
Although adults slept longer during N-2 than they did on average over the past six months, the average sleep
duration of N-1 did not dier from the average sleep time in the past six months (N-2: mean ± SD 8.9 ± 1.3 h,
p = 0.001; N-1: 8.3 ± 0.9 h; p = 0.17).
During the post-learning night (N-0), sleep duration did not dier from the average sleep duration in the
past six months, either for children (N-0: mean ± SD 9.3 ± 1.0 h, p = 0.62) or adults (N-0: mean ± SD 7.5 ± 0.8 h,
p = 0.11). However, on average children slept signicantly more than adults (p = 0.001).
Vigilance parameters. Vigilance parameters are reported in Table2.
Sleep Wake
Children Adults Children Adults
Duration <6
months (h) 9.43 ± 0.42 8.09 ± 0.92 9.7 ± 0.75 7.92 ± 1.03
Duration N-2 (h) 9.93 ± 1.25 9.03 ± 1.35 10.10 ± 0.99 8.79 ± 1.31
Duration N-1 (h) 10.12 ± 1.37 8.20 ± 1.08 10.37 ± 1.22 8.42 ± 0.69
Duration N-0 (h) 9.27 ± 1.00 7.53 ± 0.78 — —
Onset <6 months
(min) 20.00 ± 7.56 21.88 ± 19.65 19.33 ± 8.00 19.28 ± 12.58
Onset N-2 (min) 18.00 ± 17.09 21.38 ± 24.28 17.13 ± 12.32 24.28 ± 28.89
Onset N-1 (min) 22.00 ± 16.01 24.06 ± 28.89 14.67 ± 13.43 16.39 ± 13.92
Onset N-0 (min) 10.00 ± 9.45 32.81 ± 39.20 — —
Table 1. Sleep parameters. Mean (±SEM) amount of sleeping hours (duration) and the latency (minutes)
required to fall asleep (onset) for the last months, the two nights before the experiment (N-2 and N-1), and the
night between the experiment and the delayed retrieval session (N-0).
Sleep Wake
Children Adults Children Adults
Vigilance Index
(ms) 7.20 ± 40.67 10.19 ± 16.70 2.88 ± 30.32 5.34 ± 16.37
PVT session 1
(ms) 460 ± 87.66 341.25 ± 31.18 425.07 ± 66.72 352.94 ± 29.21
PVT session 2
(ms) 452 ± 85.48 331.06 ± 29.43 424.87 ± 55.02 347.61 ± 29.14
Table 2. Vigilance parameters. Psychomotor vigilance task (PVT). Mean (± SEM) for the vigilance index (ms)
obtained by subtracting mean reaction times (RTs) in the delayed session from mean RTs in the immediate
session (ms), PVT mean RTs at the rst session (1) and PVT mean RTs at the second session (2).
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A repeated measures ANOVA analysis was conducted on Reaction Times (RTs) with one within-subject factor
SESSION (immediate retrieval, IR vs. delayed retrieval, DR) and two between-subjects factors CONDITION
(Sleep vs. Wake) and AGE GROUP (Children vs. Adults). Results did not show any main eect of session or of
condition nor interaction eect between these factors (all ps > 0.10). A main eect of age group [F1,60 = 52.32;
p = 0.00001; η2 = 0,465] was observed, with faster RTs in adults than in children (Children: mean ± SD
440.8 ± 74.8 ms; Adults: 343.6 ± 30.2 ms). Hence, vigilance performance remained stable between both retrieval
sessions in both conditions for children and for adults.
Memory retention performance: age-related and sleep eects. A t-test for independent groups
showed that the number of trials needed to reach the successful criterion (60% of correct responses) in the
learning session did not dier between children and adults (Children: mean ± SD trials 1.57 ± 0.68 vs. Adults:
1.65 ± 0.54, p = 0.6, see Fig.1A). A Bayesian t-test for independent groups also supported the null hypothesis
(BF = 0.113), indicating that the learning task diculty was comparable between children and adults. Likewise, a
factorial ANOVA analysis conducted on IR performance with between-subjectsfactors AGE GROUP (Children
vs. Adults) and CONDITION (Sleep vs. Wake) did not show any main eect of AGE GROUP [F1,60 = 2.11;
p = 0.15; η2 = 0.034] or CONDITION [F1,60 = 3.18; p = 0.08; η2 = 0.050], nor an interaction eect [F1,60 = 2.61;
p = 0.11; η2 = 0.042], suggesting a comparable task diculty between age groups and conditions (see Fig.1B).
Descriptive analyses performed on retention indices (i.e., % correct responses at the DR – IR) showed that,
aer a night of sleep, children successfully recalled 1.87 ± 4.86% more denitions at DR in comparison with IR.
Aer the same night of sleep, adults forgot on average 4.75 ± 4.84% of the denitions they were able to retrieve
in the evening the day before (IR session). In the Wake condition, both age groups forgot a similar amount of
learned information between the DR and the IR sessions (Children: 2.53 ± 2.56%; Adults: 4.67 ± 3.56%).
To statistically probe the eect of age on sleep-dependent memory consolidation, a factorial ANOVA analysis
conducted on the retention indices was performed with two between-subjects factors, namely AGE GROUP
Figure 1. Learning performance (mean ± s.e.m.). (A) Number of trials to achieve the success criterion of 60%
for children (N = 15) and adults (N = 16) in the Sleep condition and for children (N = 15) and adults (N = 18) in
the Wake condition. (B) Immediate retention performance (% of correctresponses for the immediate retrieval
session occurring directly aer the learning session) for children (N = 15) and adults (N = 16) in the Sleep
condition and for children (N = 15) and adults (N = 18) in the Wake condition.
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(Children vs. Adults) and CONDITION (Sleep vs. Wake). Results showed a main effect of AGE GROUP
[F1,60 = 18.45; p = 0.001; η2 = 0.235] and CONDITION [F1,60 = 4.49; p = 0.04; η2 = 0.070] as well as a signicant
AGE GROUP by CONDITION interaction [F1,60 = 4.85; p = 0.03; η2 = 0.075]. Post-Hoc Tukey tests showed that
in the Sleep condition, children had higher retention indices than adults (p = 0.00003), whereas retention indices
did not dier between age groups in the Wake condition (p = 0.06) (see Fig.2). e Bayesian t-test with AGE
GROUP as the between-subjects factor supported the hypothesis in the Sleep condition (BF = 4.36; p = 0.001)
and was not conclusive in the Wake condition (BF = 0.76).
Finally, correlation analyses showed that sleep duration and sleep onset on the experiment night were not cor-
related with the retention indices (Sleep duration: Pearson correlation (2-tailed) r = 0.164; p = 0.38; Sleep onset:
Pearson correlation (2-tailed) r = 0.05; p = 0.80) (Fig.2).
is study demonstrates stronger overnight gains of declarative memory retrieval performance in children com-
pared with adults. Our results showed that aer a night of sleep, in children, memory retention performance
was stabilized (i.e., there was no memory loss, reecting successful consolidation22) between the immediate and
delayed retrieval sessions while memory retrieval performance decreased in adults. Importantly, delayed retrieval
performance decreased both in children and adults aer an equivalent interval of wakefulness, strengthening the
specic eect of sleep on the age-related dierences observed in our study.
Given the higher proportion of SWS in children than adults and considering the crucial role of this sleep
stage for memory consolidation9,15,18, several authors hypothesized a developmental advantage of sleep for mem-
ory consolidation processes in children22,23,34. Highly consistent with this hypothesis, our results are surprisingly
the rst to show this eect. Previous studies did not highlight improved sleep-dependent memory consolida-
tion performance in children compared with adults22,30. In these studies, the lack of age-related dierences on
sleep-dependent memory consolidation performance was explained bypotential unbalanced learning-related
pre-existing representations between children and adults22,34. Reinforcing this idea, animal studies showed that
larger schemas in long-term memory boost memory consolidation processes31,32.
is study addressed this issue by using a learning material that was equally novel for adults and children. is
allowed us to accurately compare age-related dierences of sleep on memory consolidation performance. Results
conrmed that both children and adults showed equivalent learning performance at the immediate retrieval
session and needed a similar number of trials to reach the successful learning criterion (60%). us, contrary to
previous studies, our results cannot be explained by an unbalanced task diculty between adults and children.
Sleep parameters and vigilance performance were also carefully controlled at each retrieval session in both age
groups. We observed comparable vigilance performance between retrieval sessions (IR vs. DR) and experimen-
tal conditions (Sleep vs. Wake) in children and adults. ese observations excluded a potential contribution of
circadian or vigilance eects on the observed sleep-dependent dierences between age groups. Sleep parameters
were also assessed by self-reported questionnaires and were equivalent between both age-groups apart from the
number of hours of sleep which was, as expected, higherin children thanin adults. Correlations between hours
of sleep and retention performance did not reach signicance, similarly to previous ndings suggesting that
retention performance may not be dependent on the total amount of sleep, but more specically on SWS rates36.
SWS has been related to hippocampal activation37 and hippocampus-dependent memory consolidation pro-
cesses6. Related to a dialogue between neocortical and (para)-hippocampal areas, it has been hypothesized that
SWS would trigger better memory consolidation by transferring new information from the hippocampus and
the para-hippocampus, the intermediate storage areas, to the neocortex for long-term storage and integration
into memory networks8,10,34. Remarkably, up to pubertal age, children show more SWS15,16 than adults. In this
respect, our results provide additional support for the crucial role of sleep for memory consolidation processes
during childhood. Our ndings suggest that age-related dierences in memory retrieval performance specically
observed aer a night of sleep are related to a benecial role of SWS for children compared with adults. Future
neurophysiological studies are needed to conrm this hypothesis.
Figure 2. Memory retention performance (mean ± s.e.m). Retention indices (percentage of correct responses at
delayed retrieval minus percentage of correct responses at immediate retrieval) in children (N = 15) and adults
(N = 16) in the Sleep condition and in children (N = 15) and adults (N = 18) in the Wake condition. Asterisks
indicate a signicant dierence between age groups (children VS adults): *p 0.05 or **p 0.01.
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We expected children to benet more from sleep than adults to consolidate memories, a prediction conrmed
by our data. However, an overnight decrease of performance in adults was unexpected, since several studies
showed a benet of sleep on declarative memory consolidation performance in adults8,22,26. One explanation
could be that, in adults, totally novel representations are poorly consolidated by post-training sleep, as prior
knowledge seems to be a prerequisite for new memories to be consolidated during sleep3840. In that line, stud-
ies in rodents31,32 have highlighted a strong impact of retroactive interference on totally new representations.
New information related to pre-existing knowledge seems less sensitive to retroactive interference, and there-
fore features a slower deterioration rate. Moreover, the declarative memory network contribution to successful
memory retrieval is enhanced for the schema-congruent relative to schema-incongruent memories in adults39,40.
Interestingly, Brod et al. (2017) showed that hippocampal and neocortical contributions during a retrieval session
were not dependent on pre-existing knowledge in children. However, in adults, activation of the declarative mem-
ory networks signicantly depended on the congruence of the new information with prior learning41. Hence, in
line with these previous studies, our results suggest that pre-existing schemas wield a specic eect on memory
consolidation processes in adults, which does not seem to be the case in children.
In conclusion, the present study supports the importance of sleep and its impact on learning processes dur-
ing childhood. By comparing sleep-dependent memory consolidation performance between children and adults
diering on the amount of SWS15,16,18, and by showing the specic advantage of sleep in children on memory
consolidation performance, our experiment presumed to advance the study of brain mechanisms underlying
age-related changes in sleep-dependent memory consolidation processes. Hence, our ndings open up novel ave-
nues to investigate how age-related changes in SWS-dependent memory consolidation processes may be related
to dierent underlying neurophysiological processes in children and adults both in the context of typical or atyp-
ical developmental conditions.
Limitation section. We acknowledge limitations in the present study that could be addressed in the future.
First, we did not record electrophysiological sleep parameters and therefore could not quantify SWS in our young
and adult populations, or search for potential correlations with overnight changes in memory performance.
However, we believe that it does not hamper the validity of our main conclusions based on the known dierences
in SWS between prepubertal and adult populations. Over the past 15 years, developmental studies have consist-
ently demonstrated that the amount of SWS drastically decreases with age across the maturational process (see
Kurdziel, 20199, for a recent and detailed review on this topic). From 6 years old to prepubertal age, the SWS rate
as well as its dierent characteristics are quite similar despite age dierences17,18. Across puberty, SWS rate sharply
declines in association with a decrease of cortical connectivity resulting from brain maturation and reduced
synaptic density15,19,20 and continue to decrease with age16,18. For instance, Kurth et al. (2010) showed that while
prepubertal children (12 years old) exhibited a SWS rate of 28.1 (±2.8) % per night, mature adolescents already
showed a signicant decrease in SWS rate with 19.3 (±1.7) % per night21. us, according to these numerous
developmental studies and, as we compared school-age children (7–12 years) and adults (20–30 years), we assume
that SWS durations per night dier signicantly between populations without overlap in our study. We also chose
not to obtain EEG recordings in this study, to have children and adults sleeping in more natural conditions.
Second, due to the absence of interference in the sleep condition, one may hypothesize that sleep may act as a
“temporary shelter” that simply postpones the eect of interference and, thereby, passively maintains the mem-
ory traces. However, compelling evidence have critically challenged this view and showed that sleep-dependent
gains in memory performance do not solely result on the basis of reduced interference but depend on an active
role of sleep. At the behavioural level, Ellenbogen and coll. demonstrated in two important behavioural studies
not only that sleep improves recall of verbal memories despite the presence of retroactive interference but also
that sleep renders these newly formed memories more resistant, especially when it is challenged with interfer-
ence42,43. In addition to these studies, a great body of neurophysiological studies also demonstrate the active role
of sleep in consolidating memory. In particular, several studies showed, using polysomnographic recordings,
that sleep-dependent improvements in performance were associated with a specic sleep stage (e.g. SWS but not
REM sleep or Sleep stage 2)4447. Furthermore, neuroimaging studies conducted in adults showed reactivation of
learning-related cerebral areas during sleep and that the amplitude of these activations were correlated with the
amount of overnight gains in performance6,48. Altogether, these studies demonstrated that sleep plays an active
role in declarative memory consolidation processes, thus, rejecting critics asserting that the benecial impact of
sleep on memory performance results from a passive and temporary protection against interference that would
otherwise be observed during wakefulness.
For future directions, we believe that further studies should investigate changes in sleep-dependent memory
consolidation processes across various developmental age groups, including younger children (<7 years old) and
adolescents (12–18 years old). is may also help better understand how sleep-dependent memory consolidation
changes may dierentially impact academic performance and general cognitive abilities. In particular, compar-
ing these aspects before and aer adolescence should provide us with important information, as a substantial
decrease in the SWS rate (for a similar night of sleep) occurs during this developmental period15,21,4951. We also
suggest future work to investigate the link between sleep disorders and learning disabilities, as evidence shows
an association between atypical sleep patterns in children (e.g., interictal epileptic activity during slow sleep) and
memory diculties23,5256.
Participants. e initial sample was composed of 87 participants including 39 adults (25 women; mean ±
SD age: 23,90 ± 2,12 years; range, 20–30 years) and 48 children (24 girls; mean ± SD age: 9,67 ± 1,78 years; range,
7–12 years). All participants and legally authorized representatives for participants age below 18 gave written
informed consent before their inclusion in this study approved by the local Biomedical Ethics Committee [CUB
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Hôpital Erasme - Université Libre de Bruxelles (ULB, 018/2016)]. All participants were native French speakers.
ey had no medication or neurological, learning or language disabilities or developmental delay history.
Participants were asked to respect their usual sleep habits at least the 2 nights preceding the experiment. Sleep
quality and sleep habits over the past month were assessed using the Pittsburgh Sleep Quality Index (PSQI)57 for
adults, or the Sleep Disturbances Scale for Children (SDSC)58 for children. To estimate the maintenance of the
sleep habits during at least two nights prior the experimental night and during the experiment, sleep duration
and latency were assessed using the St. Mary’s Hospital Sleep Questionnaire59. As retrieval sessions occurred at
dierent times of the day depending on the experimental condition, circadian chronotypes and vigilance states
were carefully controlled to avoid any time-of-the-day eect or vigilance variation on retention performance.
Circadian chronotype was assessed with the Morningness-Eveningness Questionnaire in adults (MEQ)60 and
with the Children Morningness-Eveningness Preference in children (CMEP)61. Participants with an extreme cir-
cadian chronotype were excluded.
Vigilance state was assessed at each retrieval (delayed and immediate) session using the Psychomotor
Vigilance Task (PVT, 5 minutes-duration version)62, according to standards in the eld63. Participants were asked
to press a button as fast as possible each time a digital counter started, with the reaction time as a depend-
ent measure. e PVT-task is a gold standard measure to detect changes in vigilance related to circadian varia-
tions6264. e PVT is also routinely used in sleep and memory studies to control for a possible impact of variation
in vigilance state on learning and performance measures8,29,6367. To control for such confound in our protocol, we
administered the PVT to our participants both in the morning and the evening sessions.
e nal sample was composed of 64 healthy subjects aer exclusion of participants with (i) abnormal sleep
habits, quantity or quality before or during the experimental night, (ii) extreme circadian chronotype, (iii) sig-
nicant dierence of vigilance between retrieval sessions. e nal sample included 34 adults (21 women; mean
± SD age: 23.8 ± 2,22 years; range, 20–30 years) and 30 children (17 girls; mean ± SD age: 9.7 ± 1,77 years;
range, 7–12 years). All participants were randomly assigned either to a sleep [Sleep, 15 children (mean ± SD age:
9.47 ± 1,64 years; 8 girls); 16 adults (mean ± SD age: 23.0 ± 2,39 years; 10 women)] or a wake [Wake, 15 children
(mean ± SD age: 9,87 ± 1,92 years; 10 girls); 18 adults (mean ± SD age: 24,5 ± 1,86 years; 11 women)] condition.
Adults received a nancial compensation while children received a gi voucher for their participation in the
Materials. One hundred colored 2D outline drawings of unfamiliar non-objects (see Fig.3A) created by the
same artist and paired using PHOTOSHOP 2 in terms of size (6×6 cm on screen), intensity, colors and contrast
were used. Non-objects were directly adapted from two existing databases68. All the NO were presented on the
same 17 inch screen laptop for all participants, at a distance of 80 cm of the eyes, with a 4°x4° visual angle. e
idiosyncratic character of the to-be-learned material was conrmed by a pre-test performed with a separate group
of children (N = 37) to ensure that none of those non-objects were associated with any meaning. Each of the
non-objects was randomly associated with a denition of the object’s magical (imaginary) function (e.g., With
this object you can “open any doors”, “see through the walls”, “stop the rain”, “quickly heal wounds”, “read people’s
thoughts”). All denitions were in French and were 4 to 7 words long. Four lists of 50 to-be-learned stimuli (ran-
domly selected from the set of 100 non-objects) were created in counterbalanced order. One list was assigned to
each participant at the learning session (see Fig.3B). A complete description of the properties of the material and
learning task can be found in Urbain et al. (2013a, 2016).
Learning and Retrieval sessions and Experimental procedure. All participants were tested at home
during 3 sessions: a learning session, an Immediate Retrieval (IR) session and a Delayed Retrieval (DR) session.
All sessions were conducted in a quiet environment. In the Sleep condition, the learning and IR sessions occurred
in the evening while the DR session occurred in the morning aer a night of sleep. In the Wake condition, learn-
ing and IR took place in the morning, and DR in the evening without a sleep interval (see Fig.3C).
During the learning session, all participants learned the 50 “magical” functions of each non-object. e learn-
ing session included ten learning blocks during which each participant learned ve non-objects. For each learn-
ing trial, a non-object was presented on the computer screen by the experimenter who mentioned its magical
function aloud to the participant. en, each non-object was presented during 150 ms followed by 850 ms of a
white screen and nally a question mark indicating to the participant to repeat the function they had just been
taught (see Fig.3B). Aer each ve non-objects, a recapitulative test (including ve non-objects) was adminis-
tered. Feedback with correct responses was given to the participant during this ve-by-ve learning session but
not during the IR or DR session (see below; a detailed description of the learning procedure is provided in Urbain
et al., 2013a).
e IR session occurred immediately aer the learning session. During the IR session, the 50 non-objects were
again presented one by one randomly. As for the learning session, each non-object was presented during the IR
session for 150 ms, followed by 850 ms of a white screen, and then the question mark indicating to the participant
to formulate the answer (the most complete denition; or “I skip” in case of forgotten items). Participants had to
correctly retrieve at least 60% of the novel verbal associations during that IR session that followed the learning
session. If the participant did not achieve a 60% success rate, the learning session restarted only presenting the
forgotten items. Once the success criterion was reached, meaning that the participant succeeded in remembering
at least 30 denitions out of 50, the IR session was completed.
e DR session occurred at home, on average eleven hours (10–12 hours) aer the IR session and in exactly
the same conditions except that no success criterion had to be reached. To avoid potential eects of sleep inertia,
the DR session in the Sleep condition and the learning Session in the Wake condition occurred one hour aer
participants woke up.
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Data acquisition and analyses. Retrieval performance at IR and DR was encoded using a computer pro-
gram (MATLAB 6.1 R12.1, Mathworks, Sherbom, MA, 2004). Additionally, participants’ oral responses were
recorded for qualitative purpose. Statistical analyses were conducted using STATISTICA 12 soware (TIBCO
SOFTWARE, California, USA, 2016).
Declarative memory retention performance was computed using a retention index (%), subtracting the per-
centage of correct responses at DR from the percentage of correct responses at IR for each participant. Analyses
were then conducted using a factorial ANOVA on the retention indices with two between-subject factors AGE
GROUP (Children vs. Adults) and CONDITION (Sleep vs. Wake). Post hoc Tuckey tests were used to decompose
ANOVA eects. Bayesian t-tests analyses were also conducted to provide further evidence in favor of either the
null or the experimental hypothesis. Bayes Factors (BF) are interpretable as an odds ratio and a default mode
for Bayesian t-test69. A BF value less than 1/3 is viewed as strong supportive evidence for the null hypothesis
(i.e., no dierence between groups) whereas BF values > 3 strongly support the experimental hypothesis of
between-group dierences. An intermediate BF value (between 1/3 and 3) is viewed as inconclusive.
To ensure that memory performance at immediate and delayed retrieval sessions was not confounded by a
circadian eect in both conditions (Sleep: evening-morning vs. Wake: morning-evening) or vigilance state, vig-
ilance was assessed at each retrieval (delayed vs. immediate) session using the PVT task. Analyses consisted of
a repeated measure ANOVA on PVT mean reaction times (RTs) with a within-subjects factor SESSION (IR vs.
DR) and two between-subjects factors AGE GROUP (Children vs. Adults) and CONDITION (Sleep vs. Wake).
Student’s t-tests for independent samples (or if variance were unequal, Welch’s t-tests) were computed to assess
potential dierences between groups or conditions on sleep parameters or the number of trials needed to reach
the successful learning criterion. In the Sleep condition, correlational analyses were conducted between sleep
onset or sleep duration on the experiment night (N0) and memory retention indices.
e signicance level was set at p < 0.05.
Received: 10 December 2019; Accepted: 26 May 2020;
Published: xx xx xxxx
Figure 3. Experimental task and procedure. (A) Picture denition task: at each session, children and adults
were asked to provide the denition of the non-object presented on the screen. Responses had to be given
aer the appearance of the question mark (1 s aer stimulus onset). (B) Sample illustrations of the 50 non-
objects used. (C) Experimental protocol: children and adults had to learn the denition of the 50 non-objects
presented in the morning (Wake condition) or in the evening (Sleep condition) and directly retrieve it during
the immediate retrieval session. Psychomotor vigilance was also assessed using the 5-minutes of the PVT. Aer
a 10–12-h retention interval lled with sleep (children, N =15 ; adults, N = 16) or wakefulness (children, N = 15;
adults, N = 18), a delayed retrieval of the 50 magical functions associated to the non-objects occurred, followed
by the 5-minutes psychomotor vigilance task.
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is work was supported by a grant of the Fonds de la Recherche Scientique (FRS-FNRS, Belgium: CREDIT
DE RECHERCHE: n° 29149840) - project “e role of slow sleep oscillations and associated brain connectivity
mechanisms in memory consolidation and executive functions”.We would also like to thank Prof M. J. Taylor for
her precious help in proofreading the manuscript.
Author contributions
Conceived and designed the experiments: C.U. Performed the experiments: A.P. and M.B. Analyzed the data: A.P.
and C.U. Wrote the manuscript: A.P. and C.U. All authors reviewed the manuscript.
Competing interests
e authors declare no competing interests.
Additional information
Correspondence and requests for materials should be addressed to A.P. or C.U.
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... Although much is known about how memory representations are encoded and retrieved in childhood, memory retention across longer consolidation periods is much less researched and may progress with different temporal dynamics in children who are about to start the school in comparison to adults (Peiffer et al., 2020a;Wang et al., 2018;Wilhelm et al., 2008). For instance, it has been shown that short-delay memory consolidation rate (i.e., measured after one night of sleep) is comparable between children aged 6-8 years and young adults for word-pair associates (Wilhelm et al., 2008). ...
... Memory retention rates were measured as an indirect index of memory consolidation, particularly the stabilization of initially encoded information, by keeping encoding comparable and retrieval demands low across all time points. We hypothesized no differences in short-delay memory consolidation between children and young adults (Peiffer et al., 2020a;Wang et al., 2018), but less robust long-delay consolidation in children in comparison to young adults (Ghetti and Bunge, 2012;Lebel et al., 2012;Shing et al., 2010). Furthermore, we applied a partial least squares correlation analysis (PLSC) to map behavioural memory consolidation measures (i.e., retention rate) onto multiple structural regions-of-interest (ROIs) reported previously to be involved in memory processes. ...
... Children showed steeper accuracy percentage change and thus lower short and long-delay retention rates in comparison to young adults, indicating reduced retained memory of prior-knowledge-dependent complex associative information across time. On the one hand, our result is not in line with the findings of higher short-delay memory consolidation (i.e., after one night of sleep) for incidental learning episodic tasks in 7-12-years-old children in comparison to young adults (Peiffer et al., 2020a;Wang et al., 2018). These studies suggested that higher proportion of slow wave sleep in children in comparison to adults may contribute to possible age-related consolidation benefits. ...
Full-text available
From early to middle childhood, brain regions that underlie memory consolidation undergo profound maturational changes. However, there is little empirical investigation that directly relates age-related differences in brain structural measures to memory consolidation processes. The present study examined memory consolidation of intentionally studied object-location associations after one night of sleep (short delay) and after two weeks (long delay) in normally developing 5-to-7-year-old children (n = 50) and young adults (n = 39). Behavioural differences in memory retention rate were related to structural brain measures. Our results showed that children, in comparison to young adults, retained correctly learnt object-location associations less robustly over short and long delay. Moreover, using partial least squares correlation method, a unique multivariate profile comprised of specific neocortical (prefrontal, parietal, and occipital), cerebellar, and hippocampal head and subfield structures in the body was found to be associated with variation in short-delay memory retention. A different multivariate profile comprised of a reduced set of brain structures, mainly consisting of neocortical (prefrontal, parietal, and occipital), hippocampal head, and selective hippocampal subfield structures (CA1-2 and subiculum) was associated with variation in long-delay memory retention. Taken together, the results suggest that multivariate structural pattern of unique sets of brain regions are related to variations in short- and long-delay memory consolidation across children and young adults.
... Some researches expressed that both children and adolescence's performance improve in declarative memory consolidation after one night sleep. However, this improvement was not sleep related in procedural memory [7,16,31,32,41]. Other researchers found that sleep can be useful both in children and adults' declarative and procedural memory consolidation after training for a new motor skill [3,41]. ...
... Sugawara et al. [35] suggested that sleep is associated with offline skill enhancement in explicit motor sequence task in children, as in adults. Peiffer et al. [31] showed overnight gains of declarative (explicit) memory retention performance in children. However, other researchers showed that sleep, compared to wake in retention test, enhanced the consolidation of implicit motor sequence tasks. ...
... However, researchers, investigating procedural and declarative memory in children, used simple tasks which were naturally implicit (i.e., serial reaction time, implicit continuous task) or explicit (i.e., two-dimensional objects location, word-pair associates, finger tapping task) compared to adults [3,41]. However, implicit and explicit knowledge of task instructions and regulations were typically not manipulated in these sequence tasks researches [3,7,13,16,31,41]. So, considering the little evidence in children and not having enough investigations of the type of knowledge relating to the task sequence, we cannot generalize the results of the adult researches to the children. ...
Full-text available
Study aim : The purpose of this study was to investigate the role of sleep and awareness on consolidation of general and Sequence-Specific learning in children. Material and methods : Male participants (n = 48, 10 to 12 years old) were assigned to one of four groups based on awareness and sleep. Acquisition phase took place in the morning (wake groups, 8 ± am) or in the evening (sleep groups, 8 ± pm) followed by a 12 hours retention interval and a subsequent delayed retention test (1 week). Children in the explicit groups were informed about the presence of the sequence, while in the implicit groups were not informed about it. For data analysis in consolidation of general sequence learning and Sequence-Specific Consolidation phases, 2 × 2 × 2 and 2 × 2 × 3 ANOVA with repeated measures on block tests were used respectively. Results : The data provides evidence of offline enhancement of general motor learning after 12 hours which was dependent on sleep and awareness. Moreover, the information persistence after 1-week was significant only in sleep groups. The results also indicated that consolidation of sequence-specific learning was only observed after 12 hours in element duration and it was related to sleep and awareness. Conclusions : The results revealed that sleep wasn’t only an essential factor in enhancement of off-line sequence learning task after 12 hours in children, but performance of the children was dependent on awareness and sleep.
... There is also increasing evidence that the benefits of sleep on memory may be greater in children than adults. For example, one recent study lends support to this hypothesis for declarative memories, as 7-12-year-olds, but not adults, showed sleep-dependent enhancements of new object memory even when initial encoding scores did not differ (Peiffer et al. 2020). Likewise, in a separate study examining memory retention for item locations associated with high rewards, differences between sleep and daytime wake in 7-11-year-old children were more pronounced than in adults, with children showing clear forgetting over an interval awake and superior retention across overnight sleep (Prehn-Kristensen et al. 2018). ...
... As such, most studies of sleep and memory in infancy and early childhood have taken advantage of this nap window, focusing on the memory benefits of the nap alone (relative to midday wake; e.g., Esterline & Gómez 2021, He et al. 2020, Werchan & Gómez 2014, Wilhelm et al. 2012a. Conversely, sleep-dependent consolidation studies in middle childhood focus exclusively on overnight sleep (Backhaus et al. 2008;Fischer et al. 2007;Henderson et al. 2012;James et al. 2020;Munz et al. 2021;Peiffer et al. 2020;Prehn-Kristensen et al. 2013, 2009, 2011Wilhelm et al. 2008Wilhelm et al. , 2013. ...
Sleep supports memory processing. In adults, memories are consolidated to a greater extent over an interval of sleep than over intervals spent awake. Behavioral evidence supports a benefit of sleep for memory consolidation in infants and children as well. While mechanistic studies are few, current evidence supports a role in memory consolidation for slow-wave sleep in particular. Mounting evidence suggests that these effects are modulated by brain development and may evolve from infancy to adulthood. Moreover, as reviewed here, sleep benefits in infancy and early childhood may be dependent on the type of learning and sleep bout (nap versus overnight). Understanding the typical development of sleep-related memory processing is critical to understanding compromised or atypical development and to informing sleep-focused interventions to improve memory during critical periods of learning across childhood. FREE JOURNAL-SPONSORED E-COPY OF THIS ARTICLE IS AVAILABLE TO COLLEAGUES ONLINE AT
... Amongst these architectural changes are increases in the amount of nocturnal SWS as well as higher SWA over childhood, with claims that the proportion of SWS peaks at age 10e12 years (Campbell & Feinberg, 2009;Kurth et al., 2010;Ohayon et al., 2004;Wilhelm et al., 2012Wilhelm et al., , 2013. Since SWS is thought to be key for effective sleep-dependent memory consolidation and tends to account for roughly double the proportion of night time sleep in pre-early adolescents relative to adults, it has been found that direct comparisons of these age groups produces enhanced sleep-dependent consolidation effects in children (Peiffer, Brichet, De Tiege, Peigneux, & Urbain, 2020;Wilhelm et al., 2013). For word learning, Weighall et al. (2017) demonstrated that after sleep, 7-8 year-olds had greater increases in explicit memory for newly learned words than adults. ...
Memory representations of newly learned words undergo changes during nocturnal sleep, as evidenced by improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning (at least under the present conditions), and emphasize the need to better understand both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.
... Since 1955 when Aserinsky and Kleitman (1955) first assessed eye movements and their potential relationship with sleep depth in infants, there has been a constant growth in sleep research in children investigating not only sleep duration but also sleep quality and sleep physiology. Nowadays, there is consensus that sleep enhances memory consolidation for various memory domains in children, especially regarding declarative (explicit) memory (Ashworth, Hill, Karmiloff-Smith, & Dimitriou, 2014;Hahn et al., 2019;Hahn, Heib, Schabus, Hoedlmoser, & Helfrich, 2020;Peiffer, Brichet, De Tiege, Peigneux, & Urbain, 2020;Wang, Weber, Zinke, Inostroza, & Born, 2018;Wilhelm, Diekelmann, & Born, 2008). A study examining implicit and explicit knowledge for motor sequence learning (Wilhelm et al., 2013) showed that children demonstrate even greater gains in sleepdependent explicit knowledge than adults. ...
Increasingly studied in a systematic manner since the 1970s, the cognitive processes of the brain taking place during sleeping periods remain an important object of scrutiny in the scientific community. In particular, sleep has been demonstrated to play a significant role for learning and memory consolidation processes, and sleep scientists have started unravelling its underlying neurophysiological mechanisms. However, sleep remains a multidimensional phenomenon, and many questions remain left open for future research. In this selective review article, we address recent advances in particular domains in which sleep research has further progressed in the past decade. We highlight the developmental trajectory of sleep‐dependent learning and memory consolidation processes, from their development in childhood to their potential impairments in ageing, and the nature and extent of our capabilities for information processing, learning, and memory reinforcement during sleep.
... While a recent study found comparable benefits of prior knowledge on sleep-dependent memory consolidation in children [59], our findings in adolescents should not be generalized, until Density was defined as the number of spindles per minute. Subjects with more than 10 percent artifacts were removed. ...
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Study Objectives The learning brain establishes schemas (knowledge structures) that benefit subsequent learning. We investigated how sleep and having a schema might benefit initial learning followed by rearranged and expanded memoranda. We concurrently examined the contributions of sleep spindles and slow wave sleep to learning outcomes. Methods 53 adolescents were randomly assigned to an 8h Nap schedule (6.5h nocturnal sleep with a 90-minute daytime nap) or an 8h No-Nap, nocturnal-only sleep schedule. The study spanned 14 nights, simulating successive school weeks. We utilized a transitive inference task involving hierarchically ordered faces. Initial learning to set up the schema was followed by rearrangement of the hierarchy (accommodation) and hierarchy expansion (assimilation). The expanded sequence was restudied. Recall of hierarchical knowledge was tested after initial learning and at multiple points for all subsequent phases. As a control, both groups underwent a No-schema condition where the hierarchy was introduced and modified without opportunity to set up a schema. EEG accompanied the multiple sleep opportunities. Results There were main effects of Nap schedule and Schema condition evidenced by superior recall of initial learning, reordered and expanded memoranda. Improved recall was consistently associated with higher fast spindle density but not slow-wave measures. This was true for both nocturnal sleep and daytime naps. Conclusion A sleep schedule incorporating regular nap opportunities compared to one that only had nocturnal sleep benefited building of robust and flexible schemas, facilitating recall of the subsequently rearranged and expanded structured knowledge. These benefits appear to be strongly associated with fast spindles.
... Since SWS is thought to be key for effective sleep-dependent memory consolidation and tends to account for roughly double the proportion of night time sleep in pre-early adolescents relative to adults, it has been predicted that direct comparisons of these age groups will produce enhanced sleep-dependent consolidation effects in children. Aligning with this, Wilhelm et al. (2013) found that compared to adults, 8-11 year old children showed greater gains in explicit knowledge of a motor sequence following sleep, and this was related to higher nocturnal SWA (see also Peiffer et al., 2020). For word learning, Weighall et al. (2017) demonstrated that after sleep, 7-8 year-olds had greater increases in explicit memory for newly learned words than adults. ...
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Behavioural and neuroimaging data suggest that memory representations of newly learned words undergo changes during nocturnal sleep, including improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning, and emphasize the need to advance theories of word learning by better understanding both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.
... We predict that sleep will promote consolidation in both the language and motor tasks, but the benefit of sleep may be reflected differently for each task. In the language task, we predict that sleep will result in stabilization of item-specific knowledge (evident by performance on high frequency items), as was previously evident in vocabulary learning and episodic memory tasks (Gais et al., 2006;Payne et al., 2012;Peiffer et al., 2020;Tamminen et al., 2010). Based on findings of sleep related offline gains in motor sequence learning tasks (Fischer et al., 2002(Fischer et al., , 2005Karni et al., 1998;Korman et al., 2007) and the effect of sleep on grammar learning (Batterink et al., 2014), we predict that sleep will improve performance in the motor task and in linguistic tasks that rely on extraction of regularities, namely low frequency trained items and generalization to untrained items. ...
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The current study explores the effects of time and sleep on the consolidation of a novel language learning task containing both item-specific knowledge and the extraction of grammatical regularities. We also compare consolidation effects in language and motor sequence learning tasks, to ask whether consolidation mechanisms are domain general. Young adults learned to apply plural inflections to novel words based on morpho-phonological rules embedded in the input and learned to type a motor sequence using a keyboard. Participants were randomly assigned into one of two groups, practicing each task during the morning or evening hours. Both groups were retested 12 and 24 hrs. post training. Performance on frequent trained items in the language task stabilized only following sleep, consistent with a hippocampal mechanism for item-specific learning. However, regularity extraction, indicated by generalization to untrained items in the linguistic task, as well as performance on motor sequence learning, improved 24 hours post training, irrespective of the timing of sleep. This consolidation process is consistent with a fronto-striatal skill learning mechanism, common across the language and motor domains. This conclusion is further reinforced by cross domain correlations at the individual level between improvement across 24 hours in the motor task and in the low-frequency trained items in the linguistic task, which involve regularity extraction. Taken together, our results at the group and individual levels suggest that some aspects of consolidation are shared across the motor and language domains, and more specifically between motor sequence learning and grammar learning.
Behavioral pediatrics is a multidisciplinary field that involves many healthcare specialists revolving around the practicing pediatrician and primary care clinician; also, various additional, associated fields of training have developed such as developmental-behavioral pediatrics, neurodevelopmental pediatrics, pediatric psychodermatology and medical care for those of all ages with developmental disabilities (1-16). Experts in psychiatry and psychology work closely with pediatric clinicians in a variety of professional relationships, including co-located and non-co-located mental health settings (17-24). Pediatricians can provide a wide variety of care to children and adolescents with complex disorders, depending on their training as well as interests, and this book seeks to provide au courant perspectives in behavioral pediatrics (25-29). Behavioral health screening remains an important task of pediatricians and behavioral pediatricians as they evaluate their pediatric patients (30-40).
Objective This study aimed to develop, validate, and apply a scale assessing knowledge of sleep-related myths and truths and associate it with sociodemographic factors. Methods A scale with 15 questions was created, containing statements about the characteristics of sleep and related to sleep and dentistry. Each answer ranged from 0 to 4 points, generating a total score from 0 to 60, where higher scores represented greater knowledge. A preliminary study with 200 people assessed its convergent and discriminant construct validity, internal consistency, and temporal stability. The main study included 1,965 respondents over 18 years. Additionally, sociodemographic data were collected and a classification of the level of knowledge was performed. Data were analyzed with Student’s t-test and one-way ANOVA (p < 0.05). Results The questionnaire showed convergent (p < 0.001) and discriminant (p = 0.024) construct validity, internal consistency (alpha = 0.7), and temporal stability (ICC = 0.87). In the main study, 90.3% of the participants had moderate and high knowledge, with the score ranging from 24 to 58. Adults over 28 years old (p < 0.001), from the southern region of Brazil (p < 0.001), who lived in capital or metropolitan areas (p < 0.001), with higher education (p < 0.001), without religion (p < 0.001), and involved in dentistry (p < 0.001) had greater knowledge than their peers. Conclusions The scale presented good psychometric properties. Most participants had moderate and high knowledge on sleep, with a difference in knowledge related to the age, region and area of residence, education, involvement with dentistry, and religion.
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After encoding, memories undergo a transitional process termed systems memory consolidation. It allows fast acquisition of new information by the hippocampus, as well as stable storage in neocortical long-term networks, where memory is protected from interference. Whereas this process is generally thought to occur slowly over time and sleep, we recently found a rapid memory systems transition from hippocampus to posterior parietal cortex (PPC) that occurs over repeated rehearsal within one study session. Here, we use fMRI to demonstrate that this transition is stabilized over sleep, whereas wakefulness leads to a reset to naïve responses, such as observed during early encoding. The role of sleep therefore seems to go beyond providing additional rehearsal through memory trace reactivation, as previously thought. We conclude that repeated study induces systems consolidation, while sleep ensures that these transformations become stable and long lasting. Thus, sleep and repeated rehearsal jointly contribute to long-term memory consolidation.
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Sleep is the single most common form of human behavior, indicating that sleep likely has an important evolutionary function. Yet the functions of sleep are still debated. Intriguingly, sleep is not static across the life span, changing in duration, pattern, structure, and physiology. This chapter reviews the transformations of sleep, from the first appearance of sleep prenatally to sleep in older adulthood, and assesses how the functions of sleep may change in response. This review focuses on the memory function of sleep and examines sleep-dependent consolidation across declarative, procedural, and emotional memory domains. With respect to the memory function of sleep, changes in SWS in particular appear to have the greatest impact on the resultant age-related alterations in sleep-dependent memory consolidation.
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Abilities to encode and remember events in their spatiotemporal context (episodic memory) rely on brain regions that mature late during childhood and are supported by sleep. We compared the temporal dynamics of episodic memory formation and the role of sleep in this process between 62 children (8-12 years) and 57 adults (18-37 years). Subjects recalled "what-where-when" memories after a short 1-hr retention interval or after a long 10.5-hr interval containing either nocturnal sleep or daytime wakefulness. Although children showed diminished recall of episodes after 1 hr, possibly resulting from inferior encoding, unlike adults, they showed no further decrease in recall after 10.5 hr. In both age groups, episodic memory benefitted from sleep. However, children's more effective offline retention was unrelated to sleep.
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A systematic sleep questionnaire has been devised for assessing the previous night's sleep of a subject. It has been designed for repeated use. It is completed by the subject and is framed with the needs of the hospital patient in mind. In the present study it was given to 93 subjects in four different groups: 16 surgical inpatients, 21 medical inpatients, 32 psychiatric inpatients (in a general hospital unit), and 24 normal volunteers. Test retest reliability correlations have been derived using a nonparametric correlation coefficient (Kendall's tau). Each of the items achieved statistically significant reliability (p < 0.0001) in all four groups, with the value for tau on the total sample varying from 0.70 to 0.96. The St. Mary's (or SMH) Sleep Questionnaire is put forward as an instrument that is a systematic inquiry into the subject's experience of sleep and that is composed of items of demonstrable reliability.
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Prior knowledge speeds up system consolidation and accelerates integration of newly acquired memories into existing neocortical knowledge networks. By using targeted memory reactivations, we demonstrate that prior knowledge is also essential for successful reactivation and consolidation of memories during sleep, both on the behavioral and oscillatory level (i.e., theta and fast spindle activity). Thus, prior knowledge is a prerequisite for new memories to enter processes of system consolidation during sleep.
Sleep disturbances in children with neurodevelopmental disabilities are very common. While sleep problems in these children are usually not significantly different compared to those of typically developing children, they are often more chronic and severe, more challenging to treat, and more than one type of sleep disturbance is common. Due to the high prevalence of sleep disturbances in this population, it is important for clinicians to systematically screen for sleep problems and to perform a thorough sleep evaluation once problems are identified. This evaluation should be based on a very detailed sleep history, including a comprehensive description of the presenting complaint(s), sleep schedules and sleep habits, as well as daytime sleepiness and behavioral issues and/or mood changes related to sleep. The evaluation should include a medical history, developmental/school history, family history, psychosocial history, behavioral assessment, and physical examination. The clinician should be familiar with the appropriate indications for and interpretation of sleep diagnostic tools, such as sleep diaries, overnight polysomnogram, multiple sleep latency test, and actigraphy.
Over the 40 years that TINS has been in existence, there has been substantial progress in understanding the types, organisation, and neural mechanisms of memory. The selectivity of memory maintenance and retention remains a puzzle, and we here summarise two contributions of our own research to this enigma: the striking impact of the novelty and surprise often of other events happening around the time that a new memory is encoded and how activated prior knowledge guides the updating process that characterises aspects of memory consolidation.
Objectives: To provide evidence-based recommendations and guidance to the public regarding indicators of good sleep quality across the life-span. Methods: The National Sleep Foundation assembled a panel of experts from the sleep community and representatives appointed by stakeholder organizations (Sleep Quality Consensus Panel). A systematic literature review identified 277 studies meeting inclusion criteria. Abstracts and full-text articles were provided to the panelists for review and discussion. A modified Delphi RAND/UCLA Appropriateness Method with 3 rounds of voting was used to determine agreement. Results: Foremost of the sleep continuity variables (sleep latency, number of awakenings N5 minutes, wake after sleep onset, and sleep efficiency), the panel members agreed that these measures were appropriate indicators of good sleep quality across the life-span. However, overall, there was less or no consensus regarding sleep architecture or nap-related variables as elements of good sleep quality. Conclusions: There is consensus among experts regarding some indicators of sleep quality among otherwise healthy individuals. Education and public health initiatives regarding good sleep quality will require sustained and collaborative efforts from multiple stakeholders. Future research should explore how sleep architecture and naps relate to sleep quality. Implications and limitations of the consensus recommendations are discussed.