Immediate as well as delayed post learning sleep but not wakefulness enhances declarative memory consolidation in children

While there is mounting evidence for the importance of sleep for declarative memory consolidation in adults, so far this issue has not been investigated in children despite considerable differences in sleep duration and sleep architecture between children and adults. Here, 27 children (aged between 9 and 12yr) were examined on two conditions: on the Sleep-Wake condition, subjects learned word pairs in the evening and delayed recall was tested first in the next morning after sleep and then again in the following evening after daytime wakefulness. On the Wake-Sleep condition, learning took place in the morning and delayed recall was tested in the evening of the same day and again in the next morning after sleep. In both conditions retention of declarative memory was significantly increased only after an interval of sleep that either followed immediately after learning (as in the Sleep-Wake condition) or that followed after daytime wakefulness (as in the Wake-Sleep condition), respectively. The results support the hypothesis that sleep plays an active role in declarative memory consolidation even if delayed and further show for the first time the importance of sleep for declarative memory consolidation during childhood.     

Sleep enhances memory consolidation in the hippocampus-dependent object-place recognition task in rats

The positive impact of sleep on memory consolidation has been shown for human subjects in numerous studies, but there is still sparse knowledge on this topic in rats, one of the most prominent model species in neuroscience research. Here, we examined the role of sleep in the object-place recognition task, a task closely comparable to tasks typically applied for testing human declarative memory: It is a one-trial task, hippocampus-dependent, not stressful and can be repeated within the same animal. A test session consisted of the Sample trial, followed by a 2-h retention interval and a Test trial, the latter examining the memory the rat had for the places of two objects presented at the Sample trial. In Experiment 1, each rat was tested twice, with the retention interval taking place either in the morning or evening, i.e., in the inactive or active phase, respectively. Rats showed significantly (p<0.01) better memory for object place after the Morning session. To control for confounding circadian factors, in Experiment 2 rats were tested four times, i.e., in the morning or in the evening while sleep was or was not deprived. Sleep during the retention interval was recorded polysomnographically. Rats only showed significant memory for the target object place in the Test trial after the Morning retention interval in the absence of sleep deprivation, and recognition performance in this condition was significantly superior to that in the three other conditions (p<0.05). EEG recordings during spontaneous morning sleep revealed increased slow oscillation (0.85-2.0 Hz) and upper delta (2.0-4.0 Hz), but reduced spindle band (10.5-13.5 Hz) activity, as compared to evening sleep. However, spindle band power was increased in the Morning retention interval in comparison to a Morning Baseline period (p<0.05). We conclude that consolidation of object-place memory depends on sleep, and presumably requires NonREM sleep rich in both slow wave and spindle activity.     

Atypicalities in sleep and semantic consolidation in autism

Sleep is known to support the neocortical consolidation of declarative memory, including the acquisition of new language. Autism spectrum disorder (ASD) is often characterized by both sleep and language learning difficulties, but few studies have explored a potential connection between the two. Here, 54 children with and without ASD (matched on age, nonverbal ability and vocabulary) were taught nine rare animal names (e.g., pipa). Memory was assessed via definitions, naming and speeded semantic decision tasks immediately after learning (pre‐sleep), the next day (post‐sleep, with a night of polysomnography between pre‐ and post‐sleep tests) and roughly 1 month later (follow‐up). Both groups showed comparable performance at pre‐test and similar levels of overnight change on all tasks; but at follow‐up children with ASD showed significantly greater forgetting of the unique features of the new animals (e.g., pipa is a flat frog). Children with ASD had significantly lower central non‐rapid eye movement (NREM) sigma power. Associations between spindle properties and overnight changes in speeded semantic decisions differed by group. For the TD group, spindle duration predicted overnight changes in responses to novel animals but not familiar animals, reinforcing a role for sleep in the stabilization of new semantic knowledge. For the ASD group, sigma power and spindle duration were associated with improvements in responses to novel and particularly familiar animals, perhaps reflecting more general sleep‐associated improvements in task performance. Plausibly, microstructural sleep atypicalities in children with ASD and differences in how information is prioritized for consolidation may lead to cumulative consolidation difficulties, compromising the quality of newly formed semantic representations in long‐term memory.     

The reciprocal relation between sleep and memory in infancy: Memory‐dependent adjustment of sleep spindles and spindle‐dependent improvement of memories

Sleep spindle activity in infants supports their formation of generalized memories during sleep, indicating that specific sleep processes affect the consolidation of memories early in life. Characteristics of sleep spindles depend on the infant's developmental state and are known to be associated with trait‐like factors such as intelligence. It is, however, largely unknown which state‐like factors affect sleep spindles in infancy. By varying infants’ wake experience in a within‐subject design, here we provide evidence for a learning‐ and memory‐dependent modulation of infant spindle activity. In a lexical‐semantic learning session before a nap, 14‐ to 16‐month‐old infants were exposed to unknown words as labels for exemplars of unknown object categories. In a memory test on the next day, generalization to novel category exemplars was tested. In a nonlearning control session preceding a nap on another day, the same infants heard known words as labels for exemplars of already known categories. Central–parietal fast sleep spindles increased after the encoding of unknown object–word pairings compared to known pairings, evidencing that an infant's spindle activity varies depending on its prior knowledge for newly encoded information. Correlations suggest that enhanced spindle activity was particularly triggered, when similar unknown pairings were not generalized immediately during encoding. The spindle increase triggered by previously not generalized object–word pairings, moreover, boosted the formation of generalized memories for these pairings. Overall, the results provide first evidence for a fine‐tuned regulation of infant sleep quality according to current consolidation requirements, which improves the infant long‐term memory for new experiences.     

Sleep and Affective Brain Regulation

Rapidly emerging evidence continues to describe an intimate and causal relationship between sleep and affective brain regulation. These findings are mirrored by long‐standing clinical observations demonstrating that nearly all mood and anxiety disorders co‐occur with one or more abnormalities of sleep. This review aims to (1) provide a synthesis of recent human evidence describing affective brain and behavioral benefits of sleep when it is obtained, and conversely, detrimental impairments following a lack thereof, (2) set forth a rapid eye movement sleep hypothesis of affective brain homeostasis, optimally preparing the organism for next‐day social and emotional functioning, and (3) outline how this model may explain the prevalent relationships observed between sleep and affective disorders, including relevant treatment mechanisms, with a particular focus on post‐traumatic stress disorder (PTSD).     

Sequential patterns in post-reinforcement pauses on fixed-interval schedules of food

Responding by one pigeon was reinforced with food on fixed-interval schedules of 30, 60, and 300 sec duration. A second pigeon was studied under fixed-interval durations of 60 and 300 sec. For both birds, the average post-reinforcement pause was one-half the duration of the fixed interval. Autocorrelation coefficients revealed first-order sequential dependencies in series of post-reinforcement pauses. On the 300-sec fixed-interval schedule, successive post-reinforcement tended to alternate between long and short durations. At the shorter fixed-interval durations there was less evidence of alternation sequences. A second experiment was conducted to determine if the time intervals between the first response after reinforcement and the next reinforcement (the work periods) were responsible for the alternation patterns in the series of post-reinforcement pauses. To evaluate the role of the work period, several procedures were used to modify the work period from that obtained on the fixed-interval 300-sec schedule. Adding a schedule to the fixed-interval schedule that set the minimum amount of time that could elapse between the first response after reinforcement and the next reinforcement eliminated the alternation pattern. Control schedules indicated that the elimination of alternation patterns resulted from constraints on the work period per se and not from confounded changes in the interreinforcement intervals.     

Temporal control of periodic schedules: signal properties of reinforcement and blackout

Pigeons were exposed to periodic food-reinforcement schedules in which intervals ended with equal probability in either reinforcement or brief blackout. The effects on the pattern of key pecking of sequential probability of reinforcement, interval duration, and time to reinforcement opportunity were investigated in three experiments. The major results were: (1) at short absolute interval durations, time to reinforcement opportunity determined both postreinforcement and postblackout pause (time to first key peck within an interval); (2) at long intervals, postblackout pause was consistently shorter than postreinforcement pause, even if both events signalled the same time to the next reinforcement opportunity (omission effect); (3) when reinforcement and blackout signalled different times to the next reinforcement opportunity, within the same experiment, there was some evidence for interactions analogous to behavioral contrast.     

Involvement of spindles in memory consolidation is slow wave sleep-specific

Both sleep spindles and slow oscillations have been implicated in sleep-dependent memory consolidation. Whereas spindles occur during both light and deep sleep, slow oscillations are restricted to deep sleep, raising the possibility of greater consolidation-related spindle involvement during deep sleep. We assessed declarative memory retention over an interval containing a nap and determined spindle density for light and deep sleep separately. In deep sleep, spindle density was considerably higher and showed a strong and robust positive correlation with retention. This relation was absent for light sleep, suggesting that the potentiating effects of spindles are tied to their co-occurrence with slow oscillations.     

Sleep directly following learning benefits consolidation of spatial associative memory

The last decade has brought forth convincing evidence for a role of sleep in non-declarative memory. A similar function of sleep in episodic memory is supported by various correlational studies, but direct evidence is limited. Here we show that cued recall of face-location associations is significantly higher following a 12-h retention interval containing sleep than following an equally long period of waking. Furthermore, retention is significantly higher over a 24-h sleep-wake interval than over an equally long wake-sleep interval. This difference occurs because retention during sleep was significantly better when sleep followed learning directly, rather than after a day of waking. These data demonstrate a beneficial effect of sleep on memory that cannot be explained solely as a consequence of reduced interference. Rather, our findings suggest a competitive consolidation process, in which the fate of a memory depends, at least in part, on its relative stability at sleep onset: Strong memories tend to be preserved, while weaker memories erode still further. An important aspect of memory consolidation may thus result from the removal of irrelevant memory "debris."     

1s范围视听时距认知的分段性研究

时距认知分段性指不同长度时距加工机制和表征方式不同。以往研究对1s范围时距认知分段性仍存在分歧,为此在规避以往研究局限基础上设计实验1和实验2。实验1和实验2分别采用双任务范式探讨心算任务对100ms和1000ms听、视时距比较的选择性干扰,结果表明,心算任务影响了1000ms听、视时距比较的75%差别阈限,心算加工负荷越大,75%差别阈限越大,但对100ms听、视时距比较的75%差别阈限没有影响。两项实验支持了1s范围视、听时距认知均具有分段性。     

What drives sleep-dependent memory consolidation: Greater gain or less loss?

When memory is tested after a delay, performance is typically better if the retention interval includes sleep. However, it is unclear what accounts for this well-established effect. It is possible that sleep enhances the retrieval of information, but it is also possible that sleep protects against memory loss that normally occurs during waking activity. We developed a new research approach to investigate these possibilities. Participants learned a list of paired-associate items and were tested on the items after a 12-h interval that included waking or sleep. We analyzed the number of items gained versus the number of items lost across time. The sleep condition showed more items gained and fewer items lost than did the wake condition. Furthermore, the difference between the conditions (favoring sleep) in lost items was greater than the difference in gain, suggesting that loss prevention may primarily account for the effect of sleep on declarative memory consolidation. This finding may serve as an empirical constraint on theories of memory consolidation.     

Trends in timing of sleep in the general population of Norway: 1980 to 20001

The aim of the current study was to examine whether the timing of sleep have changed over the last two decades. As part of a general survey of activities throughout the 24-hr. cycle, collected in 1980, 1990, and 2000 by Statistics Norway, information on sleep timing was obtained for every 15-min. interval for 1 wk. All three samples were representative of Norwegians. The age span was from 16 to 74 years. Timing of sleep was significantly delayed in 2000 compared to 1990 and especially so in 1980, but with no change in total amount of sleep. From 1980 to 2000, there was an increasing discrepancy in sleep or wake timing between weekdays and weekends. The current analyses show that people sleep as much as before but do so at different times. The increased discrepancy between weekdays and weekends indicates that overall sleep habits are poorer now than previously.     

Exploring Socioeconomic Differences in Bedtime Behaviours and Sleep Duration in English Preschool Children

Children's sleep is critical for optimal health and development; yet sleep duration has decreased in recent decades, and many children do not have adequate sleep. Certain sleep behaviours (‘sleep hygiene’) are commonly recommended, and there is some evidence that they are associated with longer nighttime sleep. Parents of 84 British 3‐year‐old children were interviewed about their children's sleep and completed five‐night/four‐day sleep diaries documenting their children's sleep, from which daily sleep duration was estimated. Diaries were validated by actigraphy in a subgroup of children. Sleep hygiene behaviours (regular bedtime, reading at bedtime, falling asleep in bed) were associated with each other, and were more common in the high socioeconomic status compared to the low socioeconomic status group. Parents' reasons for not practicing sleep hygiene included difficulty, inability or inconvenience. Sleep hygiene behaviours were associated with significantly longer child sleep at night but not over 24 h. Longer daytime napping compensated for shorter nighttime sleep in children whose parents did not implement sleep hygiene behaviours. Parents may need to be advised that certain behaviours are associated with longer nighttime sleep and given practical advice on how to implement these behaviours. © 2014 The Authors. Infant and Child Development published by John Wiley & Sons, Ltd.     

Influences of delay and rate of reinforcement on discrete-trial choice

An adjusting procedure was used to measure pigeons' preferences among alternatives that differed in the duration of a delay before reinforcement and of an intertrial interval (ITI) after reinforcement. In most conditions, a peck at a red key led to a fixed delay, followed by reinforcement, a fixed ITI, and then the beginning of the next trial. A peck at a green key led to an adjustable delay, reinforcement, and then the next trial began without an ITI. The purpose of the adjusting delay was to estimate an indifference point, or a delay that made a subject approximately indifferent between the two alternatives. As the ITI for the red key increased from 0 s to 60 s, the green-key delay at the indifference point increased systematically but only slightly. The fact that there was some increase showed that pigeons' choices were controlled by more than simply the delay to the next reinforcer. One interpretation of these results is that besides delay of reinforcement, rate of reinforcement also influenced choice. However, an analysis that ignored reinforcement rate, but considered the delays between a choice response and the reinforcers on subsequent trials, was able to account for most of the obtained increases in green-key delays. It was concluded that in this type of discrete-trial situation, rate of reinforcement exerts little control over choice behavior, and perhaps none at all.     

Delayed Bedtimes Are Associated With More Severe Obsessive-Compulsive Symptoms in Intensive Residential Treatment

Delays in behavioral and biological circadian rhythms (e.g., sleep timing, melatonin secretion) are found more frequently in individuals with severe and treatment-resistant obsessive-compulsive disorder (OCD). In recent years, it has been documented that these delays in behavioral and biological circadian rhythms are associated with more severe OCD symptoms and poorer response to some OCD treatments. This study examined self-reported sleep behaviors in individuals taking part in an intensive treatment for OCD and the relations between these and OCD symptoms (both at admission to and discharge from the treatment program). Replicating previous findings in less severe populations, delayed sleep phases were relatively common in this group and later bedtimes were associated with more severe OCD symptoms at admission. Sleep onset latency and sleep duration were not associated with OCD symptom severity at admission. Later bedtimes were not associated with self-reported depression or worry symptom severity. There was no evidence of sleep behaviors affecting change in OCD symptoms from admission to discharge from treatment—however, later bedtimes at admission were associated with more severe OCD symptoms at admission and discharge from treatment. There was no evidence of sleep onset latency or sleep duration having a similar predictive effect. More severe OCD symptoms at admission were also associated with later bedtimes at admission and discharge from treatment. These bidirectional predictive relations between late bedtimes and OCD symptoms were of small effect size but support the potential value of evaluating sleep timing in individuals with severe and/or treatment-resistant OCD.     

Subjective shortening with filled and unfilled auditory and visual intervals in humans?

Two experiments tested humans on a memory for duration task based on the method of Wearden and Ferrara (1993), which had previously provided evidence for subjective shortening in memory for stimulus duration. Auditory stimuli were tones (filled) or click-defined intervals (unfilled). Filled visual stimuli were either squares or lines, with the unfilled interval being the time between two line presentations. In Experiment 1, good evidence for subjective shortening was found when filled and unfilled visual stimuli, or filled auditory stimuli, were used, but evidence for subjective shortening with unfilled auditory stimuli was more ambiguous. Experiment 2 used a simplified variant of the Wearden and Ferrara task, and evidence for subjective shortening was obtained from all four stimulus types.     

Day-to-day variability in nap duration predicts medical morbidity in older adults

Objective: The objectives for the present study were to (a) examine within-person variability of nap duration and (b) assess how variability in nap duration is related to the number of health conditions in a sample of older adults. For highly variable behaviors such as sleep, it is important to consider fluctuations within the person instead of solely comparing averages of behaviors across persons. Method: Data were drawn from a previous study examining sleep in 103 community-dwelling older adults. Subjective estimates of napping behavior were obtained from sleep diaries and objective estimates of napping behavior were obtained using actigraphy. Both measures were collected for 14 consecutive days. The sampled data were aggregated in terms of (a) average daily time spent napping and (b) average within-person fluctuations in daily nap duration. The health measure consisted of the number of self-reported health conditions. Results: Both the objective and subjective measures revealed that there was considerable day-to-day fluctuation in nap duration and that variability in nap duration, not mean duration, uniquely predicted the number of health conditions, b = .03, b* = .26, t(100) = 2.71, p = .01. Conclusions: Duration of napping in older adults is a highly variable behavior, fluctuating as much within- as between-persons. Furthermore, variability in nap duration from day to day is predictive of greater medical morbidity, suggesting that clinicians should assess for inconsistencies in nap behavior in addition to duration, frequency, and timing. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Sensorimotor EEG operant conditioning: Experimental and clinical effects

Neurophysiological studies in cats have established a functional relationship between waking 12–15 Hz sensorimotor cortex rhythmic EEG activity (the sensorimotor rhythm or SMR) and a similar pattern during sleep, the sleep spindle. Both result from oscillatory thalamocortical discharge involving ventrobasal thalamus and sensorimotor cortex, and both are associated with a state of suppressed motor excitability. Enhancement of the SMR with operant conditioning methods in the cat clearly led to reduced seizure susceptibility. The experimental application of this approach to seizure control in epileptics has resulted in (A) evidence that EEG patterns can be manipulated significantly in man with operant conditioning, (B) suggestive observations concerning a potential component of pathology in epilepsy, and (C) strong preliminary evidence that SMR operant conditioning in epileptics is specifically therapeutic. Current research has focused upon the EEG during sleep in epileptics with primary motor symptomatology. This measure often reveals several hard signs of pathology. These include the presence of abnormal activity in the 4–7 Hz frequency band and the absence or disturbance of activity in the 11–15 Hz frequency band. Power spectral analysis is being utilized to quantify these sleep EEG components in five groups of epileptic patients, studied with different frequency patterns rewarded in an A-B-A design which provides for counterbalancing of order effects. Initial laboratory training is followed by 9–12 months of training at home with portable feedback equipment. Reward contingencies are reversed within each group at approximately three month intervals. Clinical EEG data, blood anticonvulsant measures and patient seizure logs supplement sleep EEG data obtained before training and after each phase of the design. Early results have again indicated specific therapeutic benefits following training of high frequency rhythmic central cortical activity.     

Conditioned stimulus informativeness governs conditioned stimulus-unconditioned stimulus associability

In a conditioning protocol, the onset of the conditioned stimulus ([CS]) provides information about when to expect reinforcement (unconditioned stimulus [US]). There are two sources of information from the CS in a delay conditioning paradigm in which the CS-US interval is fixed. The first depends on the informativeness, the degree to which CS onset reduces the average expected time to onset of the next US. The second depends only on how precisely a subject can represent a fixed-duration interval (the temporal Weber fraction). In three experiments with mice, we tested the differential impact of these two sources of information on rate of acquisition of conditioned responding (CS-US associability). In Experiment 1, we showed that associability (the inverse of trials to acquisition) increased in proportion to informativeness. In Experiment 2, we showed that fixing the duration of the US-US interval or the CS-US interval or both had no effect on associability. In Experiment 3, we equated the increase in information produced by varying the C/T ratio with the increase produced by fixing the duration of the CS-US interval. Associability increased with increased informativeness, but, as in Experiment 2, fixing the CS-US duration had no effect on associability. These results are consistent with the view that CS-US associability depends on the increased rate of reward signaled by CS onset. The results also provide further evidence that conditioned responding is temporally controlled when it emerges.     

Examining the Relationship Between Worry and Sleep: A Daily Process Approach

There is growing evidence suggesting that worry and sleep are intimately linked. However, the relationship between these two phenomena over the course of a day remains largely unstudied. It is possible that (a) worry predicts sleep disturbance that night, (b) sleep disturbance predicts worry the following day, or (c) there is a bidirectional relationship between worry and sleep disturbance. The present study examined the daily relationship between worry (both during the day and immediately prior to sleep onset) and sleep in 50 high trait worriers who were randomly assigned to one of two interventions aimed at reducing worry as part of a larger study. A daily process approach was utilized wherein participants completed daily reports of sleep and worry during a 7-day baseline period followed by a 14-day intervention period. Results of repeated measures multilevel modeling analyses indicated that worry experienced on a particular day predicted increased sleep disturbance that night during both the baseline and intervention weeks. However, there was no evidence of a bidirectional relationship as sleep characteristics did not predict worry the following day. Additionally, the type of intervention that participants engaged in did not affect the daily relationship between worry and sleep. Results of the present study are consistent with the cognitive model of insomnia (Harvey, 2002) and highlight the importance of addressing and treating worry among individuals with high trait worry and sleep disturbance.