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Sleep Improves Memory: The Effect of Sleep on Long Term Memory in Early Adolescence

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Sleep plays an important role in the consolidation of memory. This has been most clearly shown in adults for procedural memory (i.e. skills and procedures) and declarative memory (e.g. recall of facts). The effects of sleep and memory are relatively unstudied in adolescents. Declarative memory is important in school performance and consequent social functioning in adolescents. This is the first study to specifically examine the effects of normal sleep on auditory declarative memory in an early adolescent sample. Given that the majority of adolescents do not obtain the recommended amount of sleep, it is critical to study the cognitive effects of normal sleep. Forty male and female normal, healthy adolescents between the ages of ten and fourteen years old were randomly assigned to sleep and no sleep conditions. Subjects were trained on a paired-associate declarative memory task and a control working memory task at 9 am, and tested at night (12 hours later) without sleep. The same number of subjects was trained at 9 pm and tested 9 am following sleep. An increase of 20.6% in declarative memory, as measured by the number correct in a paired-associate test, following sleep was observed compared to the group which was tested at the same time interval without sleep (p<0.03). The performance on the control working memory task that involved encoding and memoranda manipulation was not affected by time of day or relationship to sleep. Declarative memory is significantly improved by sleep in a sample of normal adolescents.
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Sleep Improves Memory: The Effect of Sleep on Long
Term Memory in Early Adolescen ce
Katya Trudeau Potkin
1
*, William E. Bunney, Jr.
2
*
1 Department of Human Biology, Brown University, Providence, Rhode Island, United States of America, 2 Department of Psychiatry and Human Behavior, University of
California Irvine, Irvine, California, United States of America
Abstract
Sleep plays an important role in the consolidation of memory. This has been most clearly shown in adults for procedural
memory (i.e. skills and procedures) and declarative memory (e.g. recall of facts). The effects of sleep and memory are
relatively unstudied in adolescents. Declarative memory is important in school performance and consequent social
functioning in adolescents. This is the first study to specifically examine the effects of normal sleep on auditory declarative
memory in an early adolescent sample. Given that the majority of adolescents do not obtain the recommended amount of
sleep, it is critical to study the cognitive effects of normal sleep. Forty male and female normal, healthy adolescents between
the ages of ten and fourteen years old were randomly assigned to sleep and no sleep conditions. Subjects were trained on
a paired-associate declarative memory task and a control working memory task at 9am, and tested at night (12 hours later)
without sleep. The same number of subjects was trained at 9pm and tested 9am following sleep. An increase of 20.6% in
declarative memory, as measured by the number correct in a paired-associate test, following sleep was observed compared
to the group which was tested at the same time interval without sleep (p,0.03). The performance on the control working
memory task that involved encoding and memoranda manipulation was not affected by time of day or relationship to sleep.
Declarative memory is significantly improved by sleep in a sample of normal adolescents.
Citation: Potkin KT, Bunney WE Jr (2012) Sleep Improves Memory: The Effect of Sleep on Long Term Memory in Early Adolescence. PLoS ONE 7(8): e42191.
doi:10.1371/journal.pone.0042191
Editor: Antonio Verdejo Garcı
´
a, University of Granada, Spain
Received February 10, 2012; Accepted July 4, 2012; Published August 7, 2012
Copyright: ß 2012 Potkin, Bunney Jr. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The autho rs have no support or funding to report.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: webunney@uci.edu (WEB); katya_potkin@brown.edu (KTP)
Introduction
Several studies primarily in adults have shown that sleep
improves procedural memory, i.e. skills and procedures [1,2] as
well as declarative memory [3]. REM and slow-wave sleep
(SWS) have been implicated in memory consolidation [3–5].
Lack of REM sleep is associated with poor recall of visual
location [6]. Decline in declarative memory consolidation is
correlated with a decline in slow-wave sleep [7]. Spencer et al.
observed similar initial procedural learning in older and younger
adults; however, the older adults’ performance did not improve
following sleep, suggesting that sleep dependent memory
consolidation decreases with age [8]. This may reflect the
disturbed sleep and disrupted SWS in the elderly [3,8,9]. Slow
wave sleep increases until shortly before puberty and then shows
a prominent drop across adolescence, decreasing by more than
60% between ages 10 and 20 years [10]. It is critical to
understand the cognitive effects of normal sleep in order to
understand the consequences of disrupted sleep. This is
important since the majority of adolescents do not obtain the
recommended amount of sleep and that disrupted sleep is a key
symptom in most adolescent psychiatric and developmental
disorders [11].
Backhaus et al. studied twenty-seven children with an average
age of 10.1 years (range of nine to twelve), on a learned word pairs
list, employing a within subject design and two post-learning
assessments. They found that declarative memory was significantly
increased immediately after an interval of sleep, as well as with
delayed post-learning sleep [12]. As the authors had noted, no
control task was administered to determine if circadian confounds
were responsible for this increase in recall post sleep. Our study
addressed this limitation by administering a control task and
evaluating the effect of sleep on auditory declarative memory
consolidation in early adolescence. Visual declarative memory has
been reported to be enhanced following sleep in children;
however, auditory declarative memory has not been previously
studied [13].
Methods
Participants
Twenty female and twenty male adolescents, between the
ages of 10 and 14, were recruited in a public middle school.
The study was considered exempt by the institutional review
board because it involved the use of educational tests without
personal subject identifiers. In accord with the principals of the
Declaration of Helsinki, subjects were asked to participate in
a school class project and only told that they would be tested
two times for about 15 minutes each time. Subjects with
academic failure or accelerated academic performance or sleep
problems were not included. The subjects agreeing to partic-
ipate were grouped by sex and assigned to sleep or no sleep
conditions with a separate randomization table for each group,
to ensure a balanced design.
PLoS ONE | www.plosone.org 1 August 2012 | Volume 7 | Issue 8 | e42191
Procedures
Subjects were tested in their homes in a quiet room without
distractions for the duration of the learning and testing. The
testing sessions were conducted during weekends or during school
break. All subjects were given the paired-associate test, one of the
standard tests of declarative memory [14], which consisted of
repeating semantically related and unrelated pairs of words (e.g.
tree/leaf; lamp/shoe), in a standardized manner. After each word
pair was presented out loud, the subject repeated the pair out loud
to ensure registration of the paired associate. The list of the same
10 pairs was administered three times in immediate succession.
Subjects assigned to the sleep condition learned the paired
associates at 9:00pm (630 minutes), and were tested for cued
recall twelve hours later, after a night of sleep. The no-sleep group
received the same paired-associate presentation at 9:00am (630
minutes) and was tested for recall twelve hours later, with no
intervening sleep or naps. The control working memory task,
letter-number, was given just prior to learning the paired-associate
words and again just prior to being tested on the paired-associate
words. The letter-number test was administered to control for
possible circadian confounds and to control for attention and
encoding. The letter-number control task (LN, immediate recall
and reordering of letters and numbers) is a subtest of the WAIS-III
(Wechsler Adult Intelligence Scale) and WMS-III (Wechsler
memory Scale), the most widely used intelligence and memory
scales. An increasing long series of mixed letters and numbers is
read to the subject and the subject then orders the numbers and
letters in ascending order, e.g. b3a1 is read and subject correctly
responds with 13ab. The letters and numbers must be encoded
and then manipulated to get the correct answer. Two versions of
the letter-number task were used in random order. The number
correct was scored for the paired-associate and the letter-number
tests. The memory scores were transformed into Z scores to
determine if outliers were present; an exclusionary Z score of
62.57 was applied (1% of the normal distribution). Between group
comparisons were calculated by students t-test (2 tailed) after
testing for equal variances by Levene’s test, and ANCOVA as
necessary. Within subject comparisons were calculated by paired t-
test.
Subjects were instructed to eat their usual meals approximately
one hour before learning the paired-associates and one hour
before being tested on the paired-associates. Subjects were
instructed to get a good night’s sleep. All the subjects included
reported having had typical night of sleep and rated the quality of
the sleep as good to very good prior to the testing.
Results
The sleep group’s mean age was 12.9 compared to 12.4 for the
non-sleep group (t = (1.52), df (1,38), p = 0.14). (See Table 1 for
demographic characteristics and performance scores). There was
no statistically significant sex difference in performance for either
task.
Three outliers were identified and removed; one high scoring
subject assigned to the sleep and two lower scoring subjects
assigned to no sleep. After removing outliers, 19 sleep subjects and
18 no- sleep subjects remained. The Levene’s Test showed
equality of variances for all comparisons. The number correct on
the letter-number control task at initial testing was 6.58 for the
sleep group and 6.06 for the no-sleep group, (t = (1.54), df (1,35),
p = 0.13). The letter-number correct score on the second
administration was 6.26 and 6.33, respectively, (t = (-.16), df
(1,35), p = 0.88), (Figure 1). There was also no statistically
significant difference in performance for either group on letter-
number task between the first and second administration (paired t
test, p = 0.32 for sleep group and 0.45 for no-sleep group).
An increase of 20.6% in long-term memory (Figure 1) was
found as measured by the number correct in the paired-associate
test following sleep, compared to the group which was tested at the
same time interval, but without sleep (p,0.029). When the three
outliers are included, the number correct for recall of the paired-
associates was statistically greater for the sleep group (7.5)
compared to the no sleep group (5.9, t = (2.76), df (1,37),
p,0.009), a 32.7% increase.
Discussion
The paired-associate test is one of the standard tests of
declarative memory and has been previously used to study
declarative memory and the effects of sleep on declarative memory
in adults and children [3]. All subjects were evaluated at the same
two times of day, approximately 9 AM and 9 PM, using
standardized conditions. Performance on the paired-associate test
was significantly affected by sleep in our adolescent sample. In
contrast, working memory performance as measured by the letter-
number test, a standard subtest of the WAIS-III and WMS-III was
not affected by time of day or in relation to sleep. Correct
performance on the letter-number working memory task (LN)
requires that the letters and numbers presented to the subject must
be encoded and then correctly manipulated. We had 80% power
to detect a standardized difference of.76 correct (,11% change) or
greater, following sleep. A small difference in working memory
performance (,11%), however, may exist that could not be
detected with our sample size.
The equal performance at both sessions and between groups on
the LN supports the view that equal registration and encoding of
the memoranda was comparable at both time points and between
groups. Performance on the working memory control task did not
change with the second session for either group, suggesting that
the time of day had no effect on performance on the working
memory control task. Consequently, the observed difference in
paired-associate performance, i.e. consolidation of working mem-
ory, is most likely related to sleep itself and not any differences in
encoding. Memory consolidation has been reported to be affected
by sleep [1,2,8,9]. Both REM and slow-wave sleep have been
associated with improved memory [3–5]. Slow wave sleep
particularly enhances declarative memory.
7
.
Our results are consistent with Gais et al.’s study of young males
(mean age 17.4) showing that enhanced declarative memory was
related to periods of sleep, and not to time of day effects [15]. Naps
improve declarative memory regardless of time of nap [16] and
closely resembled memory improvement after an eight-hour night
of sleep [17]. In reviewing the timing of sleep and circadian
rhythms, Diekelmann et al. conclude that sleep promotes memory
consolidation independently of the time of day in which it occurs
[3]. Voderholzer et al. studying 14–16 year old adolescents showed
that several nights of sleep restriction did not impact memory
consolidation nor performance in a working memory task, when
two recovery night of sleep were provided, an effect they ascribed
to a compensatory enhancement of SWS [18]. The paired-
associate test begins as a working memory task and after a period
of time with consolidation becomes a declarative memory task.
Correct performance on the letter-number test and the paired-
associate tests are dependent upon encoding the memoranda.
A limitation of this study is that we did not test for encoding
strength by immediate recall after the administration of the paired-
associate test. The letter-number test requires attention and
encoding. An element of immediate recall is to prove that the
Effect of Sleep on Memory in Early Adolescence
PLoS ONE | www.plosone.org 2 August 2012 | Volume 7 | Issue 8 | e42191
subject was attending. This was assured by having the subjects
read the words (similar to other learning tests like the CERAD and
ADAS-COG) and supported by the finding of the performance on
the letter-number test. It is likely that if immediate recall following
each presentation was obtained, higher accuracy rates would have
been observed. Recent studies have demonstrated that salience
increases declarative memory performance [13,19]. Nevertheless,
our data demonstrate that sleep improves memory consolidation
even in conditions where encoding has not been reinforced.
Neither time of day or sleep affected the performance on the
letter-number test suggesting that the material was being learned
and encoded. There is no evidence that memory consolidation
depends on time of day independent of sleep. The lack of
interference during sleep has been considered as a possible cause
of the beneficial effects of sleep on declarative memory, i.e. there
are no daytime demands to interfere with memory consolidation.
Our design tested subjects on non-school days, thus mitigating the
effects of interference of memory consolidation during the day by
learning competition and other demands of a normal school day.
Gais et al. controlled for waking associated interference and found
no effect of interference on memory [15]. In a review of
controversy regarding whether absence of interference accounts
for memory improvement during sleep, Ellenbogen at al. point out
‘‘although sleep might passively protect declarative memories from
interference, consolidation must also occur during sleep for the
memories to become resistant to interference the following day’’.
Based on their review of related animal and human studies, they
point out that ‘‘hippocampus-dependent memories are reactivated
during sleep, and that this reactivation leads to strengthened
memory traces’’, finally concluding ‘‘that specific, sleep-depen-
dent, neurobiological processes directly lead to the consolidation of
declarative memories’’ [1]. Diekelmann et al. hypothesized that
both encoding and sleep-dependent consolidation during sleep
involve prefrontal-hippocampal circuitry [3].
Children have high amounts of slow wave sleep and sleep in
general. Sleep has been shown to improve declarative and
procedural memory in children and older age groups. Subjects
were asked about their sleep and confirmed that they had a typical
night sleep, consisting of 8–10 hours of sleep, average for
adolescents [20]. We did not, however, specifically measure sleep.
Lack of sleep can result in poor cognitive performance, which was
not observed in our sample, and is consistent with the subjects’
report of a good night sleep and that poor sleepers were excluded
from the sample.
Table 1. Demographic and performance scores for subjects in the sleep (n = 19) and no sleep (n = 18) conditions with outliers
removed.
Sleep No Sleep
P
Age 12.9561.05 12.462.15 0.14
Female;Male 10;9 8;10
Reported quality of sleep 19 of 19 good 18 of 18 good
Letter-Number Correct Initial Test 6.5861.02 6.0661.06 0.13
Letter-Number Correct Second Test 6.2661.59 * 6.3361.03 * 0.88
Paired Associate Recall Correct After 12 Hours 7.3761.74 6.1161.60 0.029
*not different from initial test.
Mean 6 SD.
p’s are two-tailed tests.
doi:10.1371/journal.pone.0042191.t001
Figure 1. Average Number Correct in Sleep and No Sleep Categories. A histogram of mean number correct (6 SD) for the Paired-Associate
Test (PA) and Letter Number Test (Letter #), with (n = 19) (outliers removed) and without sleep (n = 18).
doi:10.1371/journal.pone.0042191.g001
Effect of Sleep on Memory in Early Adolescence
PLoS ONE | www.plosone.org 3 August 2012 | Volume 7 | Issue 8 | e42191
A cross-over design would have provided additional confirma-
tion at the individual subject level in contrast to our parallel group
design. Our study was limited as the sample was opportune, from
a California middle school, and was not epidemiologically based.
No subjects approached declined to participate. No accelerated or
failing students were included, although this was not a strict
exclusion criterion. There were 3% African-American, 5% Asian,
and 92% Caucasian. The sample population reflected the general
school population in this geographic area, although Asians were
underrepresented (12.8%).
Our sample size was relatively small and limited to early
adolescence, ages 10–14, although twice the sample of Prehn-
Kristensen et al. who found 10 to 13 year olds improved visual
memory following sleep, especially to emotional pictures [13]. The
10–14 age group was deliberately chosen because of the
importance of declarative memory on adolescent school perfor-
mance and related social functioning [21]. Marked changes in
sleep and sleep architecture are a defining feature of adolescence
[22]. Disorders of adolescence frequently disrupt sleep. Twenty-
five to forty percent of adolescents have sleep disorders that can
have an important effect on daytime school and consequent social
functioning [23]. Sleep disorders are even more prevalent in
adolescents with psychiatric disorders and developmental disabil-
ities [24]. It is important to have data on the effects of normal sleep
on declarative memory in normal adolescents to better understand
the consequences of lack of sleep and abnormal sleep patterns.
Given the importance of adolescent memory on school
performance and consequent social functioning, a fuller un-
derstanding of the effects of sleep on memory consolidation is
needed. Other studies are needed to investigate the specific effects
of sleep on other types of memory, such as visual, procedural, and
emotional. Understanding the role of normal sleep on memory
consolidation in adolescence is critical in identifying the con-
sequences of disrupted sleep in adolescent disorders and their
treatment.
Author Contributions
Conceived and designed the experiments: KTP WEB. Performed the
experiments: KTP. Analyzed the data: KTP WEB. Contributed reagents/
materials/analysis tools: KTP WEB. Wrote the paper: KTP WEB.
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Effect of Sleep on Memory in Early Adolescence
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Sleep deficiency is a rampant issue in modern society, serving as a pathogenic element contributing to learning and memory impairment, with heightened sensitivity observed in children. Clinical observations suggest that learning disabilities associated with insufficient sleep during adolescence can persist through adulthood, but experimental evidence for this is lacking. In this study, we examined the impact of early-life sleep deprivation (SD) on both short-term and long-term memory, tracking the effects sequentially into adulthood. We employed a modified multiple-platform method mouse model to investigate these outcomes. SD induced over a 14-day period, beginning on postnatal day 28 (PND28) in mice, led to significant impairment in long-term memory (while short-term memory remained unaffected) at PND42. Notably, this dysfunction persisted into adulthood at PND85. The specific impairment observed in long-term memory was elucidated through histopathological alterations in hippocampal neurogenesis, as evidenced by bromodeoxyuridine (BrdU) signals, observed both at PND42 and PND85. Furthermore, the hippocampal region exhibited significantly diminished protein expressions of astrocytes, characterized by lowered levels of aquaporin 4 (AQP4), a representative molecule involved in brain clearance processes, and reduced protein expressions of brain-derived neurotrophic factors. In conclusion, we have presented experimental evidence indicating that sleep deficiency-related impairment of long-term memory in adolescence can endure into adulthood. The corresponding mechanisms may indicate that the modification of astrocyte-related molecules has led to changes in hippocampal neurogenesis.
... As for the physiological impact of digital media consumption, young people tend to play video games or scroll through social media during the early hours of the night, sacrificing sleep time and quality (Hale & Guan, 2015;Pirdehghan et al., 2021;Scott & Woods, 2018). Sleep is an essential phase for brain development and functioning, providing critical time for the consolidation of memories, processing of experiences, and restoration of neural pathways (Potkin & Bunney, 2012). This chronic lack of sleep exposes children and adolescents to negative cognitive consequences, such as issues with attention, memory, and learning (Peracchia & Curcio, 2018;Weaver et al., 2010;Wolfe et al., 2014), as well as affective issues, such as anxiety and depressive moods (Bastos et al., 2023;Pires et al., 2012;Talbot et al., 2010). ...
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This report explores the potential implications of rapidly integrating Artificial Intelligence (AI) applications into children's environments. The introduction of AI in our daily lives necessitates scrutiny considering the significant role of the environment in shaping cognition, socio-emotional skills, and behaviors, especially during the first 25 years of cerebral development. As AI becomes prevalent in educational and leisure activities, it will significantly modify the experiences of children and adolescents, presenting both challenges and opportunities for their developmental trajectories. This analysis was informed by consulting with 15 experts from pertinent disciplines (AI, product development, child development, and neurosciences), along with a comprehensive review of scientific literature on children development and child-technology interactions. Overall, AI experts anticipate that AI will transform leisure activities, revolutionize education, and redefine human-machine interactions. While AI offers substantial benefits in fostering interactive engagement, it also poses risks that require careful considerations, especially during sensitive developmental periods. The report advocates for proactive international collaboration across multiple disciplines and increased research into how technological innovations affect child development. Such efforts are crucial for designing a sustainable and ethical future for the next generation through specific child-centered regulations, and helping to educate all potential stakeholders (regulators, developers, parents and educators, children) about responsible AI use and its potential impacts on child development.
... Without enough sleep, we do not reactivate neural regularities, causing a lack of memories to transfer from the hippocampus to the neocortex. The hippocampus is responsible for short-term memory, while the neocortex is responsible for long-term memory [1]. One way we could go about solving the issue of extraneous variables could be to remove the subject and account for all unwanted movement variables before re-introducing the subject into the environment. ...
Conference Paper
This study introduces a new approach to tackling insomnia aimed at international students. It offers a comprehensive solution using environmental sensors and an integrated app. The motivation for this comes from many young students who have insomnia triggered by a new environment. The absence of sleep due to moving around and joining a new culture make it hard to accomplish many things. This app records sleep variables such as motion, light, ambient light, temperature, humidity, and sound. The data is then sent to a database to be pulled and analyzed. The app allows users to quickly and easily view sleep data and trends in real time with a calendar for date selection and viewing trends. When an environmental variable is deemed out of the range of widely accepted ideal sleep values, the app will give the user suggestions on what to correct. Experimental testing was conducted to assess the accuracy of the sensors and the algorithms used to translate that to viewable qualitative data for the user. We found that with using a frame differencing algorithm, there would need to be no motion of the physical camera throughout the night. A second discovery was that multiple people within the frame may affect the user's sleep data. Compared to existing methodologies, the app distinguishes itself by considering a range of environmental factors that offer subjective as well as objective sleep quality tracking. It also gives users the opportunity to form bonds and help each other on the community page. In conclusion, this product presents a reliable, cheap, and easy-to-use method to evaluate and correct sleep health as well as tackle sleep-related medical issues such as insomnia.
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Anxiety affects 4.4-million children in the USA with an onset between childhood and adolescence, a period marked by neural changes that impact emotions and memory. Negative overgeneralization – or responding similarly to innocuous events that share features with past aversive experiences – is common in anxiety but remains mechanistically underspecified. The nucleus reuniens (RE) has been considered a crucial candidate in the modulation of memory specificity. Our study investigated its activation and functional connectivity with the medial prefrontal cortex (mPFC) and hippocampus (HPC) as neurobiological mechanisms of negative overgeneralization in anxious youth. As part of a secondary data analysis, we examined data from 34 participants between 9 and 14 years of age (mean age ± SD, 11.4 ± 2.0 years; 16 females) with varying degrees of anxiety severity. During the Study session participants rated images as negative, neutral, and positive. After 12 h, participants returned for a Test session, where they performed a memory recognition test with repeated (targets) and similar (lures) images. Labeling negative relative to neutral lures as “old” (false alarms) was our operational definition of negative overgeneralization. Negative relative to neutral false alarmed stimuli displayed elevated RE activation (at Study and Test) and increased functional connectivity with the Cornu Ammonis (CA) 1 (at Test). Elevated anxiety severity was associated with reductions in the RE-mPFC functional coupling for neutral relative to negative stimuli. Exploratory analyses revealed similar patterns in activation and functional connectivity with positive stimuli. Our findings demonstrate the importance of the RE in negative overgeneralization and anxiety.
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The brain encodes huge amounts of information, but only a small fraction is stored for a longer time. There is now compelling evidence that the long-term storage of memories preferentially occurs during sleep. However, the factors mediating the selectivity of sleep-associated memory consolidation are poorly understood. Here, we show that the mere expectancy that a memory will be used in a future test determines whether or not sleep significantly benefits consolidation of this memory. Human subjects learned declarative memories (word paired associates) before retention periods of sleep or wakefulness. Postlearning sleep compared with wakefulness produced a strong improvement at delayed retrieval only if the subjects had been informed about the retrieval test after the learning period. If they had not been informed, retrieval after retention sleep did not differ from that after the wake retention interval. Retention during the wake intervals was not affected by retrieval expectancy. Retrieval expectancy also enhanced sleep-associated consolidation of visuospatial (two-dimensional object location task) and procedural motor memories (finger sequence tapping). Subjects expecting the retrieval displayed a robust increase in slow oscillation activity and sleep spindle count during postlearning slow-wave sleep (SWS). Sleep-associated consolidation of declarative memory was strongly correlated to slow oscillation activity and spindle count, but only if the subjects expected the retrieval test. In conclusion, our work shows that sleep preferentially benefits consolidation of memories that are relevant for future behavior, presumably through a SWS-dependent reprocessing of these memories.
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Adolescence is marked by dramatic changes in sleep. Older adolescents go to bed later, have an increased preference for evening activities, and sleep less than younger adolescents. This behavior change is driven by external factors, notably increased pressures from academic, social, and extracurricular activities and by biological circadian factors. There are also substantial changes in sleep architecture across adolescence, with dramatic declines in slow wave sleep, and slow wave activity (delta, ~ 0.5-4.5 Hz). These changes are associated with underlying changes in brain structure and organization, with a decrease in synaptic density likely underlying the reduction in high amplitude slow waveforms. While changes in sleep across adolescence are a normal part of development, many adolescents are getting insufficient sleep and are consequently, less likely to perform well at school, more likely to develop mood-related disturbances, be obese, and are at greater risk for traffic accidents, alcohol and drug abuse.
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Healthy aging is characterized by a diminished quality of sleep with decreased sleep duration and increased time awake after sleep onset. Older adults awaken more frequently and tend to awaken less from rapid eye movement (REM) sleep and more from non-REM (nREM) sleep than young adults. Sleep architecture also begins changing in middle age leading to a dramatic decrease in the deepest stage of nREM-slow wave sleep (SWS)-as aging progresses. Other less marked nREM changes include reduced numbers of sleep spindles and K-complexes. In contrast, the amount of REM diminishes only slightly. Both circadian and homeostatic sleep-regulatory processes are affected by aging. Circadian rhythms of temperature, melatonin, and cortisol are phase advanced and their amplitude diminished. An increased number of nocturnal awakenings and diminished daytime sleepiness suggest diminished homeostatic sleep pressure. A variety of endocrine and neuromodulatory changes (e.g., reduced growth hormone and dopamine levels) also accompany healthy aging. Healthy aging is characterized by declines in working memory and new episodic memory performance with relative sparing of semantic memory, recognition memory, and priming. Memory systems impacted by aging are associated with volumetric and functional changes in fronto-striatal circuits along with more limited changes in medial temporal structures (in which larger aging-related changes suggest neuropathology). Cross-sectional studies generally associate poorer sleep quality with poorer neuropsychological functioning. However, paradoxically, older adults appear to be more resistant to the cognitive effects of sleep deprivation, restriction, and fragmentation than younger adults. A new and expanding field examines the interaction between aging and sleep-dependent memory consolidation. Among forms of learning displaying prominent sleep-dependent consolidation in young adults, motor-sequence learning displays loss of sleep-dependent consolidation with aging whereas sleep-dependent consolidation of verbal declarative memory appears spared. Findings suggest that improving sleep through behavioral or pharmacological treatments may enhance cognition and performance in older adults.
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Adolescence is accompanied by striking changes in sleep behavior and in the phenomenology of sleep. Maturational changes in the central nervous system underlie changes in adolescent sleep structure. Sleep behaviors change during adolescence in response to maturational changes in sleep regulatory processes and competing behaviors. This pattern leads to insufficient sleep for many teens on school nights. Associations of reduced sleep with poorer school performance beg the question of how prelearning and posttraining sleep affect the learning process. Thus, insufficient sleep can impair acquisition and retrieval when sleep reduction results in sleepiness, irritability, distractibility, inattention, and lack of motivation. Strong evidence indicates that adequate sleep enhances memory consolidation and resistance to interference. Hence, insufficient sleep can also threaten learning by jeopardizing this part of the memory formation process.
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