Sleep consolidates the effector-independent representation of a motor skill

During off-line consolidation a motor skill becomes less vulnerable to interference (stabilisation) and improves in performance (enhancement). Here we examined whether off-line consolidation contributes to the process of generalisation in the extrinsic and intrinsic coordinate frame in the motor domain. Participants trained with the left hand a sequential finger tapping task that has proved sensitive to off-line consolidation. Generalisation was tested by the ability to transfer the original sequence (extrinsic transformation) or the mirror sequence (intrinsic transformation) to the right hand, and this was compared with performance on a new sequence not learned before. To determine acute effects on generalisation, transfer was assessed immediately after training of the left hand. To study the effects of off-line consolidation participants were tested after an interval of daytime (training at 8 am and retrieval test on the transfer sequences at 8 pm) or after an interval of night-time sleep (training at 8 pm and retrieval test on the transfer sequences at 8 am). Acutely, training of the left hand induced significant transfer effects to the right hand for the extrinsic transformation of the sequence, but there was no advantage for the intrinsic transformation. After a period of daytime wakefulness the transfer from the left to the right hand for the extrinsic sequence transformation had vanished and, again, there was no transfer effect for the intrinsic transformation of the sequence. By contrast, nocturnal sleep saved the initial transfer effect for the extrinsic sequence transformation. The intrinsic sequence transformation was not affected by sleep. Our results show that an effector-independent representation in an extrinsic co-ordinate frame of a skill develops soon after initial training. Sleep has the capacity to consolidate this transfer and, in this way, contributes to the generalisation of a motor skill.     

Offline consolidation of procedural skill learning is enhanced by negative emotional content

It is now well established that both procedural skills and episodic memories consolidate across periods of offline retention, and most particularly across periods of sleep. Such consolidation has been demonstrated to be more marked for emotional than for neutral episodes, but the interaction between emotionality and the offline consolidation of procedural skills has yet to be investigated. Here, we address this issue by examining the impact of an emotional background context at encoding upon the subsequent consolidation of mirror tracing, a well-studied procedural skill. We also consider the importance of sleep for such consolidation by manipulating the retention interval (over a day, overnight, or over 24 h containing normal sleep). Our data show significantly greater offline improvements in the accuracy of mirror tracing when negative emotional content is present during the training phase when compared to when neutral or positive content is present. Furthermore, consolidation across a night of sleep is associated with faster and more accurate performance than consolidation across a day of wakefulness. These novel findings show that the emotional context in which a procedural skill is learned can impact upon subsequent offline consolidation.     

The effect of daytime napping and full‐night sleep on the consolidation of declarative and procedural information

Many studies investigating sleep and memory consolidation have evaluated full‐night sleep rather than alternative sleep periods such as daytime naps. This multi‐centre study followed up on, and was compared with, an earlier full‐night study (Schabus et al., 2004) investigating the relevance of daytime naps for the consolidation of declarative and procedural memory. Seventy‐six participants were randomly assigned to a nap or wake group, and performed a declarative word‐pair association or procedural mirror‐tracing task. Performance changes from before to after a 90‐min retention interval filled with sleep or quiet wakefulness were evaluated between groups. Associations between performance changes, sleep architecture, spindles, and slow oscillations were investigated. For the declarative task we observed a trend towards stronger forgetting across a wake period compared with a nap period, and a trend towards memory increase over the full‐night. For the procedural task, accuracy was significantly decreased following daytime wakefulness, showed a trend to increase with a daytime nap, and significantly increased across full‐night sleep. For the nap protocol, neither sleep stages, spindles, nor slow oscillations predicted performance changes. A direct comparison of day and nighttime sleep revealed that daytime naps are characterized by significantly lower spindle density, but higher spindle activity and amplitude compared with full‐night sleep. In summary, data indicate that daytime naps protect procedural memories from deterioration, whereas full‐night sleep improves performance. Given behavioural and physiological differences between day and nighttime sleep, future studies should try to characterize potential differential effects of full‐night and daytime sleep with regard to sleep‐dependent memory consolidation.     

Use of targeted memory reactivation enhances skill performance during a nap and enhances declarative memory during wake in healthy young adults

Sleep is an important component of motor memory consolidation and learning, providing a critical tool to enhance training and rehabilitation. Following initial skill acquisition, memory consolidation is largely a result of non‐rapid eye movement sleep over either a full night or a nap. Targeted memory reactivation is one method used to enhance this critical process, which involves the pairing of an external cue with task performance at the time of initial motor skill acquisition, followed by replay of the same cue during sleep. Application of targeted memory reactivation during sleep leads to increased functional connectivity within task‐related brain networks and improved behavioural performance in healthy young adults. We have previously used targeted memory reactivation throughout the first two slow‐wave sleep cycles of a full night of sleep to enhance non‐dominant arm throwing accuracy in healthy young adults. Here, we aimed to determine whether application of targeted memory reactivation throughout a 1‐hr daytime nap was sufficient to enhance performance on the same non‐dominant arm throwing task in healthy young adults. Participants were allocated to either nap or no nap, and within those groups half received targeted memory reactivation throughout a 1‐hr between‐session period, leading to four groups. Only participants who slept between sessions while receiving targeted memory reactivation enhanced their throwing accuracy upon beginning the second session. Future studies will aim to use this technique as an adjunct to traditional physical rehabilitation with individuals with neurologic diagnoses such as stroke.     

Disrupted rapid eye movement sleep predicts poor declarative memory performance in post‐traumatic stress disorder

Successful memory consolidation during sleep depends on healthy slow‐wave and rapid eye movement sleep, and on successful transition across sleep stages. In post‐traumatic stress disorder, sleep is disrupted and memory is impaired, but relations between these two variables in the psychiatric condition remain unexplored. We examined whether disrupted sleep, and consequent disrupted memory consolidation, is a mechanism underlying declarative memory deficits in post‐traumatic stress disorder. We recruited three matched groups of participants: post‐traumatic stress disorder (n = 16); trauma‐exposed non‐post‐traumatic stress disorder (n = 15); and healthy control (n = 14). They completed memory tasks before and after 8 h of sleep. We measured sleep variables using sleep‐adapted electroencephalography. Post‐traumatic stress disorder‐diagnosed participants experienced significantly less sleep efficiency and rapid eye movement sleep percentage, and experienced more awakenings and wake percentage in the second half of the night than did participants in the other two groups. After sleep, post‐traumatic stress disorder‐diagnosed participants retained significantly less information on a declarative memory task than controls. Rapid eye movement percentage, wake percentage and sleep efficiency correlated with retention of information over the night. Furthermore, lower rapid eye movement percentage predicted poorer retention in post‐traumatic stress disorder‐diagnosed individuals. Our results suggest that declarative memory consolidation is disrupted during sleep in post‐traumatic stress disorder. These data are consistent with theories suggesting that sleep benefits memory consolidation via predictable neurobiological mechanisms, and that rapid eye movement disruption is more than a symptom of post‐traumatic stress disorder.     

Infrequent dream recall associated with low performance but high overnight improvement on mirror‐tracing

Although sleep facilitates learning and memory, the roles of dreaming and habitual levels of recalling dreams remain unknown. This study examined if performance and overnight improvement on a rapid eye movement sleep‐sensitive visuomotor task is associated differentially with habitually high or low dream recall frequency. As a relation between dream production and visuospatial skills has been demonstrated previously, one possibility is that frequency of dream recall will be linked to performance on visuomotor tasks such as the Mirror Tracing Task. We expected that habitually low dream recallers would perform more poorly on the Mirror Tracing Task than would high recallers and would show less task improvement following a night of sleep. Fifteen low and 20 high dream recallers slept one night each in the laboratory and performed the Mirror Tracing Task before and after sleep. Low recallers had overall worse baseline performance but a greater evening‐to‐morning improvement than did high recallers. Greater improvements in completion time in low recallers were associated with Stage 2 rather than rapid eye movement sleep. Findings support the separate notions that dreaming is related to visuomotor processes and that different levels of visuomotor skill engage different sleep‐ and dream‐related consolidation mechanisms.     

Sleep enhances memory consolidation in children

Sleep is an active state that plays an important role in the consolidation of memory. It has been found to enhance explicit memories in both adults and children. However, in contrast to adults, children do not always show a sleep‐related improvement in implicit learning. The majority of research on sleep‐dependent memory consolidation focuses on adults; hence, the current study examined sleep‐related effects on two tasks in children. Thirty‐three typically developing children aged 6–12 years took part in the study. Actigraphy was used to monitor sleep. Sleep‐dependent memory consolidation was assessed using a novel non‐word learning task and the Tower of Hanoi cognitive puzzle, which involves discovering an underlying rule to aid completion. Children were trained on the two tasks and retested following approximately equal retention intervals of both wake and sleep. After sleep, children showed significant improvements in performance of 14% on the non‐word learning task and 25% on the Tower of Hanoi task, but no significant change in score following the wake retention interval. Improved performance on the Tower of Hanoi may have been due to children consolidating explicit aspects of the task, for example rule‐learning or memory of previous sequences; thus, we propose that sleep is necessary for consolidation of explicit memory in children. Sleep quality and duration were not related to children's task performance. If such experimental sleep‐related learning enhancement is generalizable to everyday life, then it is clear that sleep plays a vital role in children's educational attainment.     

Slow Wave Sleep and REM Sleep Awakenings Do Not Affect Sleep Dependent Memory Consolidation

Study Objectives:

The effects of REM sleep and slow wave sleep (SWS) deprivation on sleep-dependent motor and declarative memory consolidation.

Design:

Randomized, within-subject, cross-over study

Setting:

Weekly (women: monthly) sleep laboratory visits, with retest 60 hours later

Participants:

Twelve healthy subjects (6 men) aged between 20 and 30 years

Interventions:

REM sleep deprivation, SWS deprivation, or undisturbed sleep

Measurements and Results:

We deprived subjects once each of REM sleep and SWS, and once let them sleep undisturbed through the night. After each night, we tested declarative and procedural memory consolidation. We tested memory performance by a verbal paired associate task and a sequential finger-tapping task at 21:00 on the study night and again 60 hours later. Although REM sleep and SWS awakenings led to a significant reduction of the respective sleep stages, memory consolidation remained unaffected. We also found a significant correlation between the declarative task and sleep spindles in the undisturbed condition, especially the sleep spindles in the first third of the night.

Conclusion:

We suggest that word-pair learning relies on stage 2 sleep spindles and requires little SWS. Their sleep dependent consolidation is not affected by SWS deprivation. Simple motor tasks may either be consolidated in stage 2 sleep or depend on only small amounts of REM sleep. Their sleep dependent consolidation is not influenced by REM sleep deprivation.

Citation:

Genzel L; Dresler M; Wehrle R; Grözinger M; Steiger A. Slow wave sleep and REM sleep awakenings do not affect sleep dependent memory consolidation. SLEEP 2009;32(3):302–310.     

Association between delayed sleep phase and hypernyctohemeral syndromes: a case study

STUDY OBJECTIVE: We investigated whether the hypernyctohemeral syndrome (non-24-hour sleep-wake syndrome) may show a clinical association with the delayed sleep phase syndrome (DSPS) in a 39-year-old woman who developed sleep disturbances following a traumatic brain injury. MEASUREMENTS AND RESULTS: Sleep-wake log documentation and wrist-activity recordings for more than 6 consecutive months confirmed the patient's tendency to live on longer-than-24-hour "days." Episodes of relative coordination to the 24-hour day were also noted, suggesting that the patient was transiently in and out of phase with environmental synchronizers too weak to fully entrain her to the geophysical environment. Interestingly, we noted a tendency to initiate sleep between 3:00 am and 5:00 am and wake up from sleep between noon and 1:00 pm. CONCLUSIONS: These results support an association between the hypernyctohemeral syndrome and the DSPS. This association may carry implications for the treatment of circadian rhythms disorders.     

Gross motor adaptation benefits from sleep after training

Sleep has been shown to facilitate the consolidation of newly acquired motor memories. However, the role of sleep in gross motor learning, especially in motor adaptation, is less clear. Thus, we investigated the effects of nocturnal sleep on the performance of a gross motor adaptation task, i.e. riding an inverse steering bicycle. Twenty‐six male participants (M = 24.19, SD = 3.70 years) were randomly assigned to a PM‐AM‐PM (n = 13) or an AM‐PM‐AM (n = 13) group, i.e. they trained in the evening/morning and were re‐tested the next morning/evening and the following evening/morning (PM‐AM‐PM/AM‐PM‐AM group) so that every participant spent one sleep as well as one wake interval between the three test sessions. Inverse cycling performance was assessed by speed (riding time) and accuracy (standard deviation of steering angle) measures. Behavioural results showed that in the PM‐AM‐PM group a night of sleep right after training stabilized performance (accuracy and speed) and was further improved over the subsequent wake interval. In the AM‐PM‐AM group, a significant performance deterioration after the initial wake interval was followed by the restoration of subjects' performance levels from right after training when a full night of sleep was granted. Regarding sleep, right hemispheric fast N2 sleep spindle activity was related to better stabilization of inverse cycling skills, thus possibly reflecting the ongoing process of updating the participants' mental model from “how to ride a bicycle” to “how to ride an inverse steering bicycle”. Our results demonstrate that sleep facilitates the consolidation of gross motor adaptation, thus adding further insights to the role of sleep for tasks with real‐life relevance.     

The contribution of nocturnal sleep to the consolidation of motor skill learning in healthy ageing and Parkinson's disease

The benefits of sleep for the consolidation of procedural motor skills are less robust in older adults, although the precise reasons for this remain unclear. To date, even less is known about these processes in older adults with neurodegenerative diseases, particularly those which impact on motor functioning. While sleep disturbance and motor symptoms are frequent disabling features of Parkinson's disease, no known studies have directly probed sleep‐dependent memory consolidation for motor skill learning in Parkinson's disease. Forty patients with idiopathic Parkinson's disease (age = 63.7 years ± 7.7; disease duration 4.1 years ± 4.4) completed a motor skill learning task pre‐ and post‐sleep and were compared to 20 age‐ and sex‐matched controls recruited from the community. Polysomnography was undertaken during the post‐training night and measures of sleep architecture were derived. Parkinson's disease patients did not demonstrate any apparent deficits in within‐session learning and overnight stabilization compared to controls, with both groups failing to demonstrate offline improvements in performance (i.e. memory consolidation). In controls, longer duration in slow wave sleep was associated with improved next‐day session learning (P = 0.007). However, in Parkinson's disease, no relationships between sleep parameters and learning measures were found. Slow wave sleep microarchitecture and the use of dopaminergic medications may contribute to impaired sleep‐dependent multi‐session acquisition of motor skill learning in Parkinson's disease.     

Circadian variations of histamine binding to lymphocytes and neutrophils and skin reactivity to histamine in atopic and healthy subjects

Introduction Numerous pathophysiological conditions change during 24-hour periods. Histamine, the main mediator in allergic reactions, exerts a multiplicity of pathophysiological actions through binding to specific receptors on effector cells. Nocturnal exacerbation of symptoms occurs in many atopic diseases in which histamine is an important mediator. Nocturnal wheezing is a very common symptom of asthma. The aim of this study was to determine whether the binding of (fluorescein-labeled) histamine to cells participating in allergic-inflammatory processes (lymphocytes, neutrophils) and skin reactivity to histamine undergo circadian changes and to compare these phenomena in atopic asthmatic and healthy subjects. Materials and Methods Blood samples were collected at 8 am, 2 pm, 8 pm, 2 am, and 8 am the next day. Histamine skin-prick tests were performed at the same times. Results It was found that skin reactivity to histamine (wheal, erythema) in healthy subjects underwent significant circadian changes with acrophase at 8 am (wheal) or 8 pm (erythema), the lowest values being at night (2 am, p = 0.017), in contrast to atopics, in whom the highest reactivity was found at night (2 am, p = 0.002). Significant differences in the binding of fluorescein-labeled histamine between day (8 am–2 pm) and night (2 am) were observed for lymphocytes (p = 0.006) and neutrophils (p = 0.018). Conclusions In the asthmatic group these changes were not significant. Circadian changes in both the binding of histamine by effector cells and skin reactivity to histamine were different in healthy and asthmatic subjects, and this may play a role in the pathomechanism, course, and chronopharmacotherapy of atopic diseases.     

Fast sleep spindle (13-15 hz) activity correlates with sleep-dependent improvement in visuomotor performance

STUDY OBJECTIVES: The relationship between memory enhancement and fast (13-16 Hz) versus slow (10-13 Hz) spindle activity during sleep was investigated. DESIGN: Standard polysomnographic recordings were conducted during an adaptation, control nonlearning, and learning night. Automatic spindle detection and measurement was utilized with visual confirmation. SETTING: Participants slept in individual, temperature-controlled bedrooms in a sleep laboratory. PARTICIPANTS: Twelve healthy student volunteers (9 women and 3 men, mean age: 22.3 years) participated. INTERVENTIONS: On the learning night, participants completed a presleep learning session on a modified version of mirror-tracing task followed by a postsleep test session. No learning or test sessions were performed on the adaptation and nonlearning nights. MEASUREMENTS AND RESULTS: Tracing time was reduced by 6.4 seconds (20.6% +/- 2.07%) from the presleep to the postsleep session. Mean amplitude and duration of fast spindles was greater on the learning night than on the nonlearning night (both P values < 0.05). Skill improvement and fast-spindle activity were positively correlated (density [r = 0.76, P < 0.01], amplitude [r = 0.69, P < 0.05], and duration [r = 0.67, P <0.05]). Significant correlations between fast-spindle activity and mirror-tracing performance were also evident for the nonlearning night. There was no significant relationship between mirror-tracing performance and slow-spindle activity on any night. CONCLUSIONS: The thalamocortical network underlying fast-spindle generation may contribute to or reflect plasticity during sleep.     

Sleep slow oscillations favour local cortical plasticity underlying the consolidation of reinforced procedural learning in human sleep

We investigated changes of slow‐wave activity and sleep slow oscillations in the night following procedural learning boosted by reinforcement learning, and how these changes correlate with behavioural output. In the Task session, participants had to reach a visual target adapting cursor's movements to compensate an angular deviation introduced experimentally, while in the Control session no deviation was applied. The task was repeated at 13:00 hours, 17:00 hours and 23:00 hours before sleep, and at 08:00 hours after sleep. The deviation angle was set at 15° (13:00 hours and 17:00 hours) and increased to 45° (reinforcement) at 23:00 hours and 08:00 hours. Both for Task and Control nights, high‐density electroencephalogram sleep recordings were carried out (23:30?19:30 hours). The Task night as compared with the Control night showed increases of: (a) slow‐wave activity (absolute power) over the whole scalp; (b) slow‐wave activity (relative power) in left centro‐parietal areas; (c) sleep slow oscillations rate in sensorimotor and premotor areas; (d) amplitude of pre‐down and up states in premotor regions, left sensorimotor and right parietal regions; (e) sigma crowning the up state in right parietal regions. After Task night, we found an improvement of task performance showing correlations with sleep slow oscillations rate in right premotor, sensorimotor and parietal regions. These findings suggest a key role of sleep slow oscillations in procedural memories consolidation. The diverse components of sleep slow oscillations selectively reflect the network activations related to the reinforced learning of a procedural visuomotor task. Indeed, areas specifically involved in the task stand out as those with a significant association between sleep slow oscillations rate and overnight improvement in task performance.     

The effect of zolpidem on memory consolidation over a night of sleep

Study Objectives: Nonrapid eye movement sleep boosts hippocampus-dependent, long-term memory formation more so than wake. Studies have pointed to several electrophysiological events that likely play a role in this process, including thalamocortical sleep spindles (12–15 Hz). However, interventional studies that directly probe the causal role of spindles in consolidation are scarce. Previous studies have used zolpidem, a GABA-A agonist, to increase sleep spindles during a daytime nap and promote hippocampal-dependent episodic memory. The current study investigated the effect of zolpidem on nighttime sleep and overnight improvement of episodic memories. Methods: We used a double-blind, placebo-controlled within-subject design to test the a priori hypothesis that zolpidem would lead to increased memory performance on a word-paired associates task by boosting spindle activity. We also explored the impact of zolpidem across a range of other spectral sleep features, including slow oscillations (0–1 Hz), delta (1–4 Hz), theta (4–8 Hz), sigma (12–15 Hz), as well as spindle–SO coupling. Results: We showed greater memory improvement after a night of sleep with zolpidem, compared to placebo, replicating a prior nap study. Additionally, zolpidem increased sigma power, decreased theta and delta power, and altered the phase angle of spindle–SO coupling, compared to placebo. Spindle density, theta power, and spindle–SO coupling were associated with next-day memory performance. Conclusions: These results are consistent with the hypothesis that sleep, specifically the timing and amount of sleep spindles, plays a causal role in the long-term formation of episodic memories. Furthermore, our results emphasize the role of nonrapid eye movement theta activity in human memory consolidation.     

Correlation between wrist activity monitor and electrophysiological measures of sleep in a simulated shiftwork environment for younger and older subjects.

Although several studies have examined the correlation between nocturnal PSG and activity measurement, validation studies of actigraphically measured sleep in shiftworking populations have not been reported. This study investigates the correlation between sleep recorded using EEG and actigraphic techniques during a simulated 12-hour shift rotation. Thirty-two subjects were allocated to groups according to age. Group (1) included sixteen subjects mean (+/- s.d.) age of 21.2 +/- 2.7 years, and Group (2) included sixteen subjects mean (+/- s.d.) age of 43.9 +/- 6.8 years. An adaptation night was followed by two 12-hour day shifts (7 am-7 pm), 24 hours off and then two 12-hour night shifts (7 pm-7 am). For the entire study subjects wore an activity monitor, and while in bed, sleep was recorded using polysomnography; both techniques were collected in 30-second epochs. A high epoch for epoch agreement between wrist activity monitoring and EEG measures of sleep was recorded for daytime and nighttime sleep periods (80-90%). There was a high correlation between EEG and actigraphically recorded sleep duration in young (0.98-0.77) and older (0.78-0.96) subjects for all sleep periods. Sleep efficiency correlations were extremely variable for both the young (0.72-0.15) and older (-0.18-0.58) subjects for daytime and nighttime sleep periods. Taken together these results suggest that wrist activity monitoring is a valid measure of sleep/wake activity and sleep duration, in a simulated shiftwork environment. However, some caution should be used for more specific measures, such as sleep efficiency particularly in older subjects.     

The use of actigraphy for assessment of the development of sleep/wake patterns in infants during the first 12 months of life

Maturation of sleep/wake patterns is one of the most important physiological developments during the first year of life. In this study, we aimed to compare the use of actigraphy and parental sleep diaries (SD) for recording the development of sleep/wake patterns longitudinally in term infants in their own home environments over the first 12 months of life. Twenty healthy term infants (7F/13M) were studied for 3 days each month in their own homes over the first 12 months of life. Sleep/wake patterns were recorded using both SD and actigraphy (AW) (AW64, Mini Mitter Co. Inc., Sunriver, OR, USA). The development of sleep and wake was analysed over 24 h, during the day (08:00-20:00 hours) and during the night (20:00-08:00 hours). A total of 186 studies had complete data sets for both analysis methods. Overall, there was no difference between methods of measurement for determination of the total percentage of sleep or wake over 24 h, or for the total percentage of sleep or wake during the day. However, at night, AW scored less time asleep (73.3 +/- 0.9%) and more time awake (26.7 +/- 0.9%) compared with the SD (80.7 +/- 1.04% and 19 +/- 1.0%, respectively, P < 0.001). Mean percentage sleep during the day decreased from 51% at 1 month to 28% at 12 months with the 1-month values being significantly higher than all other ages, while mean percentage sleep at night was only different between 1 month and 11 and 12 months. In conclusion actigraphy provides a useful tool for assessing the development infant sleep.     

Development of infant and toddler sleep patterns: real‐world data from a mobile application

The aim of this study was to investigate the development of infant and toddler sleep patterns. Data were collected on 841 children (aged from birth to 36 months) via a free, publicly available, commercially sponsored iPhone app. Analyses were conducted on caregiver recordings of 156 989 sleep sessions across a 19‐month period. Detailed visualizations of the development of sleep across the first 3 years of life are presented. In the first 3 months, sleep sessions primarily lasted less than 3.5 h throughout the day. Between 3 and 7 months old, sleep consolidated into two naps of about 1.5 h in length and a night‐time sleep session of about 10.5 h. Across age groups, a negative relationship was observed between the start of bedtime and the length of the night‐time sleep session (i.e. later bedtime is associated with a shorter night‐time sleep period). The length of daytime sleep sessions (naps) varied with age, decreasing between 1 and 5 months old, and then increasing monotonically through 28 months. Morning wake time was observed to be invariant in children aged 5–36 months. Sleep patterns are ever‐changing across the first few years with wide individual variability. Sleep patterns start to develop more clearly at 5–6 months, when longer night‐time sleep duration begins and sleep consolidation occurs. Daytime sleep patterns appeared to become more consistent and consolidated later in age than night‐time sleep. Finally, there is greater variability in bedtimes than wake times, with bedtimes having a greater influence on night‐time sleep duration.     

Development of sleep–wake rhythms during the first year of age

Circadian rhythms refer to biological rhythms that have an endogenous period length of approximately 24 hr. However, not much is known about the variance in the development of the sleep–wake rhythm. The study objectives were (a) to describe the normative variation in the development of a sleep–wake rhythm in infancy, (b) to assess whether slower development is related to sleep quality and (c) to evaluate factors that are related to the slower development of a sleep–wake rhythm. The study is based on a representative birth cohort. Questionnaires at the ages of 3 (n = 1,427) and 8 months (n = 1,302) and actigraph measurement at 8 months (n = 372) were available. Infants with significant developmental delays (n = 11) were excluded. The results are based on statistical testing and multivariate modelling. We found that the average percentage of daytime sleep was 36.3% (standard deviation [SD], 8.5%) at 3 months and 25.6% (SD, 6.6%) at 8 months. At both time‐points, infants with slower sleep–wake rhythm development slept more hours per day, had a later sleep–wake rhythm, more difficulties in settling to sleep and longer sleep‐onset latency; they also spent a longer time awake during the night. According to actigraph registrations, we found that the infants with slow development of a sleep–wake rhythm slept less and had a later start and end to night‐time sleep than the other infants. Infants’ sleep–wake rhythm development is highly variable and is related to parent‐reported and objectively measured sleep quality and quantity. Interventions to improve the sleep–wake rhythm might improve sleep quality in these infants.     

Retrograde effects of triazolam and zolpidem on sleep-dependent motor learning in humans

Drugs that act as allosteric activators at the benzodiazepine site of the gamma-aminobutyric acid (GABA_A) receptor complex are used commonly to treat insomnia but relatively little is known of how such use affects learning and memory. Although anterograde effects on memory acquisition have been shown, possible retrograde effects on consolidation are more relevant when such agents are administered at bedtime. We tested the effects of two GABA_A allosteric activators on sleep-dependent motor skill memory consolidation in 12 healthy male subjects. Subjects slept in a sleep laboratory for four consecutive nights (one accommodation night followed by three experimental nights). Placebo, triazolam 0.375 mg, and zolpidem 10 mg were given to each subject in counterbalanced order on the experimental nights. Polysomnographic (PSG) sleep measurement and sleep-dependent motor learning were assessed at each condition. Triazolam was associated with longer total sleep time and increased Stage 2 sleep. Both zolpidem and triazolam were associated with increased latency to rapid eye movement (REM) sleep. Overnight motor learning correlated with total sleep time in the placebo condition but not in the triazolam or zolpidem conditions. A statistically significant impairment in motor performance occurred overnight in the triazolam condition only. Triazolam, given in sufficient doses to prolong sleep in healthy people, affected overnight motor learning adversely. Zolpidem, in a dose sufficient to prolong REM onset latency but without other effects on PSG-measured sleep, degraded the relationship between total sleep time and overnight motor learning. These data indicate that non-selective or α1-preferring benzodiazepine site allosteric activators can interfere with sleep-dependent memory consolidation.